A classification of North American biotic communities

Biotic communities (biomes) are regional plant and animal associations within recognizable zoogeographic and floristic provinces. Using the previous works and modified terminology of biologists, ecologists, and biogeographers, we have developed an hierarchical classification system for the world's biotic communities. In use by the Arid Ecosystems Resource Group of the Environmental Protection Agency s Environmental Monitoring and Assessment Program, the Arizona Game and Fish Department, and other Southwest agencies, this classification system is formulated on the limiting effects of moisture and temperature minima on the structure and composition of vegetation while recognizing specific plant and animal adaptations to regional environments. To illustrate the applicability of the classification system, the Environmental Protection Agency has funded the preparation of a 1:10,000,000 color map depicting the major upland biotic communities of North America using an ecological color scheme that shows gradients in available plant moisture, heat and cold. Digitized and computer compatible, this hierarchical system facilitates biotic inventory and assessment, the delineation and stratification of habitats, and the identification of natural areas in need of acquisition, Moreover, the various categories of the classification are statistically testable through the use of existing climatic data, and analysis of plant and animal distributions. Both the classification system and map are therefore of potential use to those interested in preserving biotic diversity.

A Classification of North American Biotic Communities A Classification of North American Biotic Communities David E. Brown Frank Reichenbacher Susan E. Franson THE UNIVERSITY OF UTAH PRESS SALT LAKE CITY © 1998 by the University of Utah Press Al l rights reserved LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Brown, David E. (David Earl) , 1938A classification of North American biotic communities I David E. Brown, Frank Reichenbacher, Susan E. Franson. p. cm. Includes bibliographical references (p. ). ISBN 0-87480-562-7 (alk. paper) 1. Biotic communities-North America- Classification. I. Reichenbacher, Frank, 19 5 5III. Title. QH102.B76 1998 577.8 '2'097- DC21 II. Franson, Susan E., l 9 5 3- To M.D.F. (Nick) Udvardy friend, mentor, and the inspiration for this book Contents List of Figures v1 List of Tables v1 Acknowl edgments Introdu ction 2 v11 r The Biogeographic Approach 5 The C lass ifi catio n System r5 First Level 20 Second Leve l 20 Upland (Terrestrial) Formations Wetland Formations 3 Third Level 24 Fourth Leve l 24 Fifth Level 34 Sixth Level 35 Seventh Level 36 21 23 The Biotic Communities of North Am erica Map Plates 55 Literature Cited r 17 Literature Cons ulted r 29 49 Vlll Figures Hierarchy of a bulrush marsh in Great Salt Lake, Utah, to the association (sixth) level of the classification system 16 2 Biogeographic realms of North America 3 Plant formations of North America 22 4 Climatic zones of North America 26 5 A generalized map of the biotic provinces of North America 28 18 Tables Summary of the world's natural vegetation to the first level 2 Summary for the natural upland and wetland vegetation of the world to the second level 3 21 Summary for the natural upland and wetland vegetation of Nearctic and Neotropical North America to the third level 4 Nomenclature of upland biotic communities for Nearctic and Neotropical North America 5 6 21 36 Nomenclature of wetland biotic communities for Nearctic and Neotropical North America 43 Areas of North American biotic communties 5I 2 5 Acknowledgments We wish to express our gratitude to Tony Burgess, Biosphere II, Oracle, Arizona; Russell Davis, University of Arizona, Tucson; Michael Jennings, Fish and Wildlife Cooperative Research Unit and Office of Biological Services, Moscow, Idaho; Thomas R. Loveland, U.S. Geological Survey, Sioux Falls, South Dakota; W. L. Minckley, Arizona State University, Tempe; James M. Omernik, U.S. Environmental Protection Agency, Corvallis, Oregon; Barry Spicer, Data Branch Supervisor with the Arizona Game and Fish Department, Phoenix; M. D. F. Udvardy, California State University, Sacramento; Jan W. van Wagtendonk, Research Scientist with the National Park Service, Yosemite National Park, California, and Denis White, Oregon State University, Corvallis, for their editorial comments and review. Their helpful suggestions were as essential as they were thoughtprovoking and improved the manuscript immensely. Also helpful in providing photographs and information, and otherwise assisting in this project, were Randy Babb, Arizona Game and Fish Department, Phoenix; Burt Bartram, Arizona State University, Tempe; Richard E. Brown of Meadow Vista, California; Javier Diaz of Escarcega, Campeche, Mexico; Barb Dillon, R. E. Hamburg, and Peter Neubauer, Northwest Territories Economic Development and Tourism, Canada; Nancy Gray, Great Smoky Mountains National Park, Gatlinburg, Tennessee; Jeff Grathwohl, University of Utah Press, Salt Lake City; Orie Laucks, Miami University, Oxford, Ohio; Bob Lofgren, Laboratory of Tree Ring Research, University of Arizona, Tucson; Melvin Marcus, Arizona State University, Tempe (now deceased); Paul S. Martin, Department of Geosciences, University of Arizona, Tempe; Joe McAuliffe, Thom Hulen, Ted Anderson, and Patrick Quirk of the Phoenix Desert Botanical Gardens, Arizona; Roscoe Nichols, Jr., of Ciudad Mante, Tamaulipas, Mexico; David Pearson, Arizona State University, Tempe; Bob Pfister, Montana Forest and Conservation Experiment Station, Missoula; Donald Pinkava, Arizona State University, Tempe; Bonnie Swarbrick, International Wildlife Museum, Tucson, Arizona; Raymond M. Turner, University of Arizona, Tucson; and Alejandro Velezquez, Universidad Nacional Autonoma de Mexico. We are especially grateful to Bob Puterski, Las Vegas, Nevada, for preparing the r:ro,000,000 color map, to Peter Banka, Monmouth, Oregon, for preparing the figures, and to Gail Corbin, Las Vegas, Nevada, for word processing earlier versions of this manuscript. Their enthusiasm for this project was as valuable as their experience and is much appreciated. lX x Notice The U.S. Environmental Protection Agency (EPA), through its Office of Research and Development (ORD), collaborated in the research described here. This manuscript has been peer reviewed by EPA and approved for publication. Mention of trade names does not constitute endorsement or recommendation for use. I Introduction Biotic communities are regional plant formations characterized by particular species of plants and animals. Using previous works and modifying the existing terminology of biologists, ecologists, and biogeographers, we have incorporated these biotic communities in a hierarchical classification system. This classification system is formulated on the limiting effects of moisture and temperature minima on the structure and composition of vegetation as well as specific plant and animal adaptations to regional environments, and it is used by the Rangelands Group of the Environmental Protection Agency's Environmental Monitoring and Assessment Program, the Arizona and New Mexico game and fish departments, and other Southwest agencies. To illustrate the applicability of the classification system, the Environmental Protection Agency funded the preparation of a 1:10,000,000 map depicting the major upland biotic communities of North America using an ecological color scheme that shows gradients in moisture and temperature. Digitized and computercompatible, this system assists biotic inventory and assessment, the delineation and stratification of habitats, and the identification of natural areas. Moreover, the biogeographical validity of the hierarchy's various categories is statistically testable through the use of existing climatic data and an analysis of plant and animal distributions. Both the classification system and map are therefore useful to anyone interested in biotic diversity. Numerous classification systems have been created to depict and assess natural resources. In North America,,,_ these efforts have resulted in classifications and maps of potential natural vegetation (e.g., Shantz and Zon 1924; IGichler 1964, 1977; Flores Mata et al. 1971; Rzedowski 1978; Chapman 1993), forest-types (Society of American Foresters 1954; Braun 1950; Rowe 1972), life zones (Merriam et al. 1910; Holdridge 1959, 1969), wetlands (Ray 1975; Zoltai et al. 1975; Cowardin et al. 1979; Hayden, Ray, and Dolan 1984), soils and landforms (USDA Soil Conservation Service 197 5 ), land''-We follow the definition as presented in The American Heritage Dictionary of the English Language, William Morris, ed., Houghton Mifflin Co. (r98r): North America-The northern continent of the Western Hemisphere with a total area, including adjacent islands, of 9,385,000 square miles. It extends from the Colombia-Panama border in the south through Central America, the United States (except Hawaii), Canada, and the Arctic Archipelago to the northern tip of Greenland. The map, however, includes only North America, north of the Panama Canal. I 2 NORTH AMERICAN BIOTIC COMMUNITIES use (Anderson, Hardy, and Roach 1972; Anderson et al. 1976), "ecosystems" (Crowley 1967; Meidinger and Pojar 1991), "ecoregions" (Bailey 1976; Bailey and Cushwa l981;Wiken 1986; Wiken, Rubec, and Ironside 1989; Omernik 1987; Ricketts et al. 1997), land-cover (Loveland et al. 1991), and vegetation change (Eidenshink 1992). These resources have proven useful to those interested in land-use planning and the sampling and stratification of largescale units, including states (see, e.g., Frye, Brown, and McMahan 1984), provinces (Wickware and Rubec 1989; MacKinnon, Meidinger, and Klinka 1992), regions (Brown and Lowe 1980, 1994), nations (Tosi 1969; Carnahan 1976; Garrison et al. 1977; Driscoll et al. 1984; Wiken, Rubec, and Ironside 1989; Borhidi 1991), and even continents (Bailey l989a, l989b). Although most of these classifications are based on vegetation, others incorporate physiographic, climatic, soil, geographic, and chemical criteria. Some of these classifications are hierarchical (e.g., Avers et al. 1993), thus aiding land-use mapping at various scales. Several recent maps also have the advantage of being derived from high-altitude imagery and are thus applicable for the demonstration and assessment of vegetative and other changes over time (e.g., Loveland et al. 1991; Stacey and Knighton 1994). The only criticism of these classifications and maps is that their usefulness is necessarily limited by the methodology employed and the designing organization's mission, objectives, and budget. None of the above classifications, however, has been universally adopted by biologists in their efforts to classify and inventory plant and animal habitats. Systems and maps currently used by biologists either are based on existing vegetation without regard to regional plant and animal associates, or rely upon one or more land-use classifications that employ anthropogenic and other "nonbiocentric" criteria . Many of the classifications presently in use (e.g., Kuchler 1964) are nonhierarchical or only partially hierarchical. As such, these systems and maps are frequently limited and are not easily modified when higher or lower levels of assessment are desired. These limita tions have caused resource management agencies to combine, create, and adapt a variety of classification systems in their inventories of biotic resources. The result has been a proliferation of large and small scale maps, either depicting only limited areas (e.g., Brown and Lowe 1980, 1994), or employing classifications that are too broad for detailed biological enquiry (e.g., Bailey and Cushwa 1981). The profusion of classification systems has prompted national governments to seek a singular, standardized system. Canada has adopted an "official" national resource classification system (see, e.g., Wiken 1986, Meidinger and Pojar 1991, and MacKinnon, Meidinger, and Klinka 1992). Uniform vegetation classification systems have recently been proposed for Europe (Neuhaus! 1990) and for certain United States government agencies (Nature Conservancy l994a, l994b). Recently, a standardized vegetation classification system has been developed for use by all federal government agencies in the United States (U.S. Department of Interior Federal Geographic Data Committee 199 5 ). These efforts, coupled with the accelerated INTRODUCTION inventory of the world's biota and the development of high quality aerial imagery, now make biologically universal classification systems and maps possible both theoretically and practically. The need for a federal standardized method of inventorying both plant and animal habitats is obvious, given the requirements of the National Environmental Policy Act of 1969, the National Resource Planning Act of 1974, and the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program. Such a classification system, however, should not be confined to the United States and its territories. The present and increasing emphasis on endangered species residing within and outside the United States embodied in the Endangered Species Act of 1973, the North American Waterfowl Plan, the Neotropical Migratory Bird inventories now being supervised by the U.S. Fish and Wildlife Service, and the Biosphere Reserve Program being fostered by the Union for the Conservation of Nature dictate a worldwide approach to biotic assessment. While national vegetation classification systems are highly desirable for administrative purposes, these systems must also be compatible with the needs of scholars, and of those zoologists and biologists who work with international agencies. 3 1 The Biogeographic Approach Humans have long been aware that certain plants and animals were found in different areas and at different altitudes. It was not until the middle of the eighteenth century, however, that naturalists began formulating hypotheses to explain the differences and similarities they had observed. Carl Linnaeus commented on the dependence of vegetation on soil, climate, and elevation, and the French naturalist Georges Buffon postulated the effects of elevation and geographic barriers on plant and animal distribution (see Kendeigh 19 52, Udvardy 1969, and Sterling 1974 for detailed summaries of the early history of the biogeographic concept). Then, in the early l8oos, Alexander von Humboldt and his botanist accomplice Aime Bonpland wrote a series of essays laying the theoretical foundation for understanding the distribution of plants. In such works as their Geography of Plants (Humboldt and Bonpland 1807) and Humboldt's The Geographic Distribution of Plants ( l 817), they described the effects of temperature on corresponding latitudinal and altitudinal belts of vegetation in the South American Andes. Humboldt also realized that animal distributions followed similar "rules," and he is rightfully regarded as the "father of biogeography." A generation later, the great naturalist Louis Agassiz (18 54) divided the world into eight continental land masses or "realms" based on their fauna! constituents and the human races living there. This largely intuitive effort was followed by British ornithologist Phillip Lutley Sclater ( l 8 5 8 ), who presented a similar division of the world based on the then known distribution of birds. Although Sclater's six fauna! "regions" bore a strong similarity to Agassiz's "realms,'' his classification was based on a sounder theoretical basis, and his concept received wide recognition. Accordingly, Sclater's work was soon being modified and rearranged by zoologists in other fields, including other ornithologists such as Thomas Huxley (1868). Using Sclater's model, and incorporating his and Charles Darwin's theories on evolution, as well as his considerable experience with the biota of both hemispheres, A. R. Wallace (18 76) published a rationale and map dividing the world into six biogeographic "regions" based on the distribution of mammalian orders and families. Although Wallace's six regions were similar to Sclater's, Wallace went a step further and subdivided his regions into twenty-four "subregions" or "provinces" based on the then-known distribution of mammal genera and species. His Nearctic Region of North America, for example, contained a Canadian, an Eastern United States, a 5 6 NORTH AMERICAN BIOTIC COMMUNITIES Rocky Mountain, and a California province. Recognizing the importance of geographic origin and isolation as well as of climate, his Geographical Distribution of Animals soon became accepted as the standard approach to biogeography. Wallace's ideas did not go unchallenged. J. A. Allen, a contemporary American mammalogist, took strong issue with the delineations of Wallace's regions. Allen (1878, 1892) proposed instead a system of eight "realms" or "faunal areas," which, while equivalent to Wallace's regions, contained in descending rank "regions," "provinces," and, lastly, a series of "floras and faunas." Although insightful and ahead of his time (Allen recognized a circumpolar Arctic Realm, and combined Wallace's Nearctic and Palearctic regions into a "Holarctic" or North Temperate Realm), Allen's approach was less analytical than Wallace's. Partly for this reason, Allen's biogeographic classification and its hierarchy were rejected in favor of the Sclater-Wallace approach. Later, another American zoologist, Theodore Gill (l 88 5 ), compared Wallace's and Allen's systems. While generally favoring the former, Gill had a number of pertinent criticisms of both approaches. In a well-considered but now largely forgotten paper, Gill followed his predecessors' approach in dividing the world's continental land masses into large "fauna ( rea lms" on the basis of animal orders and families. As had Wallace and Allen, he used genera to delineate a hierarchy of finer "regions" and other subdivisions. Gill objected, however, to the use by Wallace and Allen of only mammals as the defining criteria in their classifications. Gill, an ichthyologist, thought that all animals should be used, including fishes. Like Wallace, Gill recognized that isolation and evolution were equally as important as temperature in determining terrestrial realms. He also noted the lack of marine forms in previous classifications- an omission only now being readdressed (see, e.g., Ray 1975, Maxwe ll et al. 1994). To correct this omission, Gill proposed the addition of six marine realms determined primarily on water temperatures-an Arctic Realm, a Paractalian or North Temperate Realm, a Tropical Realm, a Notalian or South Temperate Realm, an Antarctican Realm, and a Deep Sea or Bassalian Realm. Botanists meanwhile were hard at work developing their own phytogeographic classifications. As early as 1859, J. G. Cooper had divided North America into twenty-seven "natural provinces" and regional subdivisions, giving each one a geographic or Native American name to emphasize its geographic center. Cooper also considered climate and animal constituents in his delineations, so that his approach was biogeographic as well as vegetative. Years later, some of his designations were still being followed by L. R. Dice ( l 94 3) and other twentieth-century biogeographers in their efforts to identify biotic provinces or regions. Engler (1879-1882), a German professor of botany, was the Wallace of plant geographers, separating the world into flora l kingdoms or realms, regions, provinces, and districts analogous to Wallace's regions and provinces. Another German botany professor, THE BIOGEOGRAPHIC APPROA C H Oscar Drude (1887) would later publish the best world vegetation map for years to come. Drude was well aware of the limiting effects of climate on plant structure, and his map of vegetation life-forms or "formations" illustrates much more than vegetation per se. Besides creating and defining the formation term to designate plant structure, Drude contributed greatly to the advancement of phytogeography through his use of hierarchy and his understanding of the effects of physiographic features on plant dispersal. As was Wallace's classification, Engler's work continued to be modified by plant and animal geographers, and, in modified form, is still used today (see, e.g., Good 1964 and Walter 1973). Although continually being revised and refined (e.g., Sclater and Sclater 1889; Udvardy 1987), the Sclater-Wallace-Engler approach has stood the test of time and remains largely intact at the continental (that is, realms or regions) level. Wallace's and Engler's provinces and other lesser ranks, never intended to be definitive or final, were in need of major revision almost immediately. Rearranging and redefining these continental subdivisions continues to occupy the attention of biogeographers to the present day. As the nineteenth century came to a close, the United States was unique in that the federal government actively supported biogeographic inquiry. The idea for a national biological survey had originated in l 8 5 3 with Spencer Fullerton Baird of the National Museum's Smithsonian Institution. Baird saw to it that U.S. military expeditions had naturalists collecting examples of the expanding nation's flora and fauna. The results of these surveys were then published in lengthy tomes by the U.S. Congress. In 1885, after much bureaucratic wrangling, future government surveys became the responsibility of the U.S. Biological Survey, a bureau of the Department of Agriculture. The methodology to describe the habitats of the plants and animals collected on these surveys would now become, for better or worse, the domain of the Survey's first Chief, Clinton Hart Merriam. Merriam had been taken by his well-connected father to meet Baird in 1871 (Sterling 1977). Baird was so impressed with the fifteen-year-old Merriam that he invited him to join the F. V. Hayden Survey of western Wyoming that was to be conducted by the U.S. Geological Survey the following year. While on the Hayden Survey, Merriam visited the Great Salt Lake and much of Montana, Idaho, and Wyoming, including the Grand Tetons and the newly created Yellowstone National Park. This experience so impressed him that he embarked on a lifelong career of conducting surveys and collecting specimens. Educated at Yale and well connected in the world of Washington politics (he became a personal friend of President Theodore Roosevelt), Merriam was a logical choice to head the Biological Survey, which he helped found in 1885. Although he was later to specialize in mammals, Merriam was originally an ornithologist. An avid hunter and collector, Merriam maintained a strong interest in the geographic distribution of animals all his life. Experienced, fastidious, and a tireless worker, Merriam 7 8 NORT H AMERICAN BIOTIC COMMUNITIES appeared to be eminently suited for his role as America's chief biogeographer. He was also productive, authoring the first eleven of the Survey's North American Fauna series that he initiated in 1889 and that continued until 1959 (Murie 1959). Most importantly, he recognized, to his everlasting credit, that biogeographical understanding could not be limited by political boundaries. Accordingly, he saw to it that his agency conducted biological investigations throughout the North American continent from the Canadian Arctic to the tropical regions of Central America (see, e.g., Merriam 1903, Stejneger and Miller 1903, and Goldman 1920). In 1889 Merriam took time off from his duties in Washington to conduct a biological survey of the San Francisco Peaks and its environs in northern Arizona Territory. While conducting this investigation, Merriam and his partner Leonhard Stejneger noted, as did Humboldt, that the altitudinal belts of vegetation encountered at different elevations corresponded to the vegetation found at various latitudes. What was more, the animals they collected in these "life zones," as Merriam called them, were also similar to their latitudinal counterparts. Carefully measuring their altitudes, Merriam postulated that the single most important factor determining life zones was temperature. Based on actual observations and the collection of "i ndicator species" of plants and animals, Merriam and Stejneger's Results of a Biological Survey of the San Francisco Mountain Region and Desert of the Little Colorado in Arizona (1890) was immediately recognized as a significant contribution to the science of biogeography. Not satisfied with a regional system, Merriam (1892) expanded their findings to prepare an advanced "life areas" map of North America using mammalian distribution and other data. Merriam was convinced that his life zones could be used to describe the biological affiliation of all the plants and animals in North America. Each life zone, he concluded, was determined by temperature, with humidity, topography, and other factors being of lesser importance. To provide a scientific foundation for his life-zone theories, Merriam conducted an ex post fa cto analysis of his distribution data and postulated the effects of various temperature parameters. The northward distribution of animals and plants, he reasoned, was restricted by the total quantity of heat during the growing season when tempera tures exceeded 6°C. Conversely, he concluded that the southward distribution of species was determined by the mean temperatures experienced during the hottest six weeks of the year. Using tables of summed temperature data provided by the U.S. Weather Bureau, Merriam and his colleagues in the Survey proceeded to publish a series of articles and maps showing regional and continental life zones (see, e.g., Merriam l894a, l894b, 189 8, and Merriam et al. l9ro) . The biogeographic affiliation problem was declared solved. From now on the work of the Survey would be much simplified and its collected specimens could be pigeonholed in their proper life zone categories. Merriam's exalted position firmly established the life-zone concept as the official biogeographic classification system for the U.S. THE BIOGEOGRAPHIC APPROACH Biological Survey. Other mammalogists and ornithologists, especially in the West (e.g., Hall, Monroe, and Grinnell 1919; Hall 1946), also became strong life-zone supporters in that life zones were based on actual altitudinal gradients that could be recognized on the basis of indicator species. Even though Merriam's climatic calculations did not consider humidity, aridity, or minimum temperatures, criticism from biologists was slow in coming. Also ignored, at least for the time being, was his failure to adequately consider such factors as regional isolation. Few botanists, and none of the European zoologists, adopted Merriam's life-zone classification system. Plant geographers continued instead to construct vegetation maps based on plant formations and indicator dominants (e.g., Harshberger 1911 ; Shreve 1917; Shantz and Zon 1924). Moreover, after Merriam's departure from the Survey in l 9 ro, biologists in other institutions began to take issue with his maps and temperature data (e.g., Livingston and Shreve 1921). Not only were Merriam's temperature summations faulty and shown to be almost meaningless as limiting factors, his maps and terminology were found to have little application in the Eastern United States or the tropics (Dice 1923; Kendeigh 1932; Shelford l932a, 1945; Daubenmire 1938, 1946). After nearly fifty years of controversy, Merriam's life-zone system, initially a sound biogeographic study of a Western mountain, was repudiated on the basis of faulty premises, incorrect data, and the fact that it just did not work outside of the American West, where it remains in limited use today. Botanists in the meantime were doing better with their vegetation hierarchies, dividing the world into climatic zones, formation classes, communities, and associations (see, e.g., Clements 1916, BraunBlanquet 1932, Weaver and Clements 1938, and Kuchler 1947). After 1900, plant ecologists approached vegetation classification from several viewpoints (Whittaker 1978; Mcintosh 198 5). Following the European tradition set by Drude (1887) and Warming (1909), H. C. Cowles (1908), Frederick E. Clements (1916), and other ecologists set about classifying vegetation in the United States, as did A.G. Tansley (1923) in Great Britain. Most of these ecologists took "a top-down" or landscape physiognomy approach that classified plant communities on the basis of dominance-types (Whittaker 1978). Emphasizing structural dominants as "indicator species," Clements (1920) was especially influential in America, and his concept of the plant community as a holistic organism, which, with the cessation of disruptive influences, would progress toward a selfsustaining climax controlled by climate and edaphic (soil) conditions, was widely accepted. Another school of thought took a more formal "bottom-up" or floristic approach. Chief among these was the Braun-Blanquet (1932) system, which is widely used in both Europe and America. In this system, vegetation samples or releves are grouped into units on the basis of the similarity of the composition of character (that is, indicator) species. The basic unit in this classification is the "associa- 9 IO NORTH AMERICAN BIOTIC COMMUNITIES tion." Each association is then grouped into higher units called alliances. Alliances are, in turn, grouped into orders, and orders into classes, to produce a formal hierarchy of community classification. Even the higher units are based on floristic relationships rather than physiognomy (Whittaker 1962; Mueller-Dombois and Ellenberg 1974). The difference between these two schools is then one of landscapes vs. floristics. At the same time that Clements was espousing his plant community theories, H. A. Gleason (1926) was stressing that, rather than a plant community evolving as a whole, plants and plant species adapted individually to climatic parameters within the community or association. Forrest Shreve (19 5 r) also objected to some of Clements's concepts regarding succession. Shreve had noted that succession in the Clementian sense did not take place in desert environments, and he used the term "prevailing vegetation" rather than "climax" when describing landscapes. Later studies and evidence have tended to support both Gleason's and Shreve's views regarding these aspects (Whittaker 1978; Holling 199 5; Graham et al. 1996). Similarly, Weaver and Clements's (r 9 3 8) ideas on plant succession and climax, while earning widespread recognition (and criticism), have proven too local and unpredictable for general use. Both the physionomic and floristic approaches have strengths and weaknesses. Various regional traditions and modifications also have served to improve the vegetation classification processes of both schools (see, e.g., U.S. Department of Interior FGDC 1995, and Nature Conservancy 1997), and both schools have their adherents and their detractors, who have developed a confusing array of terminology in their efforts to describe the various units of their classifications. Nonetheless, no one system is necessarily "the best" system for all aspects of ecological inventory. Observing that vegetation samples taken by unprejudiced means yielded a large proportion of mixed, atypical, and transitional associations, Whittaker (1962) concluded that many plant species grade into other types of vegetation, and that there was a lack of "discontinuity" between communities. This "continuum" within and between communities has prompted some botanists to question whether vegetation should be classified at all. Whittaker (1962:159) thought that vegetation classification might be more art than science, and that future efforts to improve classification should be directed less toward standardization and a quest for objectivity, than toward a more realistic understanding of the process of classification and its relation to the properties of the communities involved. Using various classifications, phytogeographers have mapped the potential (that is, prevailing) natural vegetation of nations (e.g., Kuchler 1964 for the United States; Rzedowski 1978 for Mexico; and Borhidi 1991 for Cuba). Plant communities have been the basis for many state and regional maps (see, e.g., Wieslander 1935, Jensen 1947, Miller 1951, Barbour and Major 1977, and Kuchler 1977 for California). An especially innovative system based on climatic and structural criteria was devised in tropical America by Holdridge THE BIOGEOGRAPHIC APPROACH (1967). Complex, and difficult to apply without a myriad of climatological stations, Holdridge's classification system is nonetheless based on a strong theoretical foundation. Although Holdridge's formulae are not applicable to temperate America (see, e.g., MacMahon and Wieboldt 1983), his system has been used in modified form to map vegetation in Central America (e.g., Tosi 1969; Jennings 1988). Another, more "European," vegetation classification system has recently been used to successfully describe and map Cuba's natural vegetation (Borhidi 1991). Several of these recent vegetation classification systems incorporate evolutionary-based levels in their hierarchies (e.g., Takhtajan's [1986] floristic regions). For these reasons, vegetation classifications and maps are the foundation of most habitat descriptions (e.g., Carr 19 50; Leopold 19 59; Robbins, Bruun, and Zim 1966). Plant communities, however, do not necessarily correspond to animal habitats because of different evolutionary and dispersal histories (see, e.g., Dice 1923). Many plant community classifications (e.g., Braun-Blanquet 1932; Holdridge 1967; Mueller-Dombois and Ellenberg 1974) are too structurally detailed to be adopted by zoogeographers. It is also true that even when vegetation classification systems take ecological limitations such as climate into account, they often fail to consider regional isolation and other evolutionary forces (see, e.g., Wieslander 193 5, Jensen 1947, and Kuchler 1964, 1977). Nonetheless, the merging of the two disciplines-the geographic grouping of animal habitats paralleling vegetation classification systems-continues to be a useful tool for many biologists (Udvardy 1969; Maycock 1979). Recognizing the importance of plant habitats on animal distributions, zoogeographers began to use plant assemblages to elaborate on Wallace's and Gill's faunal subdivisions. Based on the number and presence of animal species and subspecies, these subdivisions became known as biotic provinces in North America and biogeographical provinces in Europe (Vestal 1914; Gleason 1926; Dice 1943; Goldman and Moore 1945; Matvejev 1961; Mclachlan and Liversidge 1962; Udvardy 1969, l97 5a, l975b, l984a, l984b). Generally speaking, biotic provinces are determined on the basis of regional climate, topography and soils, and a similarity in plant and animal constituents. As such, biotic provinces are regional fauna! and plant assemblages that share a common geologic and evolutionary history (Miller 1951; Kendeigh 1952). In essence, Merriam's 1890 life zone map of the San Francisco Peaks was a biotic province map (Daubenmire 1938). Some biologists, (e.g., Dice 1943) also considered biotic provinces as centers for ecological dispersal. The biotic equivalent of a plant formation, in a concept conceived by Clements and Shelford (1939), was the biome. Modifying earlier vegetation maps, Clements and Shelford mapped eleven biomes in North America to show the applicability of such an approach. They were not disappointed. Biologists such as Pitelka (l 94 l ), Miller (1951), and Aldrich (1967) readily adopted and adapted the biome concept in their studies, some of them substituting the term "biotic II 12 NORTH AMERICAN BIOTIC COMMUNITIES community" for biome. Although Shelford (1963) considered the biotic community designation redundant, he had used it himself (Shelford l932b), and the two terms have become almost synonymous. Nonetheless, biomes, as originally defined, did not include regional descriptions reflecting evolutionary and climatic influences, and many applications of the biome term were finer subdivisions than was originally intended. In an effort to clarify biotic terminology, Kendeigh (19 52) defined a biotic community as a biociation, each biociation having a distinctive species composition and occurring in a particular vegetation type that had become differentiated due to isolation and evolution. These biotic communities (or biociations) were in turn composed of one or more plant associations. Kendeigh also proposed that the name of each biotic community contain the type of vegetation involved, and that when it was necessary to distinguish one biotic community from another having the same type of vegetation, a geographical name also be used-e.g., California chaparral. This description fits the general understanding of a biotic community presented here. As have their plant ecologist counterparts, zoologists have come to accept Gleason's (1926) concept that individual members of a community can, and do, evolve independently of the biotic community in which they reside. Clements's (1920) view of the community as a holistic superorganism composed of a highly ordered sequence of species maturing toward a sustainable climax whose characteristics are determined by climate and soil conditions has accordingly been greatly revised (see, e.g., Whittaker 1978 and Holling 199 5 ). We no longer think of climax communities as evolvi ng superorganisms, and instead recognize the temporal and spatial nature of plant and anima l community hierarchy. Clements was a great ecologist, nonetheless, and many of his contributions remain valid in modified form . He was one of the first to note that plant and animal communities change and move with climatic shifts, and many of his ecological terms such as "disclimax" (permanently altered), "post-climax" (overmature), and "consociation" (single species dominant) remain useful landscape descriptions. Plant and animal communities remain, despite the limitations of Clements and Shelford's (1939) original concepts, a system of interacting populations having a particular structure and function (Whittaker 1962). Thus, the biotic approach is the best available tool in our efforts to describe plant and animal habitats. The advantages of a biotic-community approach over purely vegetative classification systems have been pointed out by a number of biologists, including Shelford (1945), Odum (1945), Kendeigh (1952), Udvardy (1969), and Brown, Lowe, and Pase (1980). In summary, these include, but are not limited to, the following: r. Biotic communities recognize faunal as well as floral distributions, thereby allowing inferences to be made as to the occurrence and relative abundance of specific plants and animals THE BIOGEOGRAPHIC APPROACH within a given formation-type. The biotic-community designation thus facilitates the meaningful inventory of common species as well as rare and endangered ones. For example, most populations of the eastern fox squirrel (Sciurus niger), as well as the rare and endangered red-cockaded woodpecker (Dendrocopos borealis) are contained within the Southeastern Deciduous and Evergreen Forest biotic community. 2. Biotic communities are readily recognized in the field, and their boundaries can be mapped on the basis of a formationtype's principal plant dominants and the species of plants and animals known to be present therein (i.e., indicator species). 3. In conjunction with biotic provinces, biotic communities and their subdivisions provide a hierarchical measurement of the length of time of eco logical isolation within the continental or realm level. Even when exotic plants and animals invade "native communities" to the extent of achieving ecological dominance, a total replacement of the native biota is rare, and the biotic affiliation of these now "disclimax" or "new-alien" communities can usually be readily ascertained and incorporated into the classification system. 4. Biotic communities, by their very nature, express the effects of all interacting environmenta l factors, abiotic as well as biotic, thus simplifying the classification of plant and anima l communities. Although soil properties and landform history affect water storage, and therefore determine the composition of plant communities within biotic provinces (see, e.g., Dokuchaev 1987 and McAuliffe 1995 ), our understanding of soil types is insufficient to predict which biotic community will be present on a given soil type (edaphic climax). And, even though certain plant communities, and even local plant formations, may be restricted to serpentines, gypsum, or other specia l soil types, the complexity involved precludes using soil type and other abiotic factors to construct a biotic classification system. Rather, it appears more reasonable to let the biotic components of a community indicate which soil types are likely to be present. 5. Although biotic comm unities are initially identified and delineated on the basis of plant dominants, an increasing body of data on indicator species now permits the relative ranking of various biotic communities by comparing the percentages of common plants and animals present (or absent) at the genus, species, and subspecies levels. Furthermore, the "reality" of biotic communities can be statistically evaluated by testing differences in seasonalclimatic data, degrees of endemism, and similarities and differences in species composition (see, e.g., Pearson and Cassola 1992 and Pearson 1994) . 6. The biotic community designation is flexible; units may be added, combined, or deleted as research and analysis warrants. Moreover, the inclusion of biotic communities in a classification system incorporates more than a century of effort in the development of zoogeographic and phytogeographic systematics. N ORTH AMER ICA N BIOTIC COMMUN ITIES Although no habitat classification system based on a biogeographic hierarchy and using biotic community concepts has yet received universal acceptance, systems based on such an integrated approach are becoming increasingly common (e.g., Driscoll et al. 1984; Pojar, Klinka, and Meidinger 1987; Bailey l989a, l989b; Neuhaus! 1990; Meidinger and Pojar 1991; Avers et al. 1993; Demarchi 1993). Even among those biologists who consider the concept of biotic communities as an "obsolete science," in that it is no longer believed that plant and animal dominants form discrete communities, these basic descriptions remain the backbone of discussions pertaining to plantanimal habitat relationships. Ecologists who view communities as a non-discrete and dynamic continuum find that they cannot resist the logic, convenience, and descriptive value of geographically and ecologically pigeonholing the various assemblages of plants and anima ls living within certain physical conditions and parameters. This acceptance is encouraging in that biologists have long utilized and benefited from the analogous perceived order of hierarchical systematics in plants and animals (Linnaeus 1758, Simpson 1961). 2 The Classification System "On two main points every system yet proposed, or that probably can be proposed, is open to objection; they are,1stly, that the several regions are not of equal rank; 2ndly, that they are not equally applicable to all classes ... " -Alfred Russel Wallace, 1876 Modifying the existing works and terminology of other biologists, ecologists, and biogeographers, Brown, Lowe, and Pase (1979, 1980) developed a hierarchical classification system for the biotic communities of North America. This classification system depends on natural criteria and recognizes the limiting effects of moisture and temperature minima as well as evolutionary origin on the structure and composition of plant and animal communities. The system was originally developed for southwestern North America where its adaptability was demonstrated for both natural and human-altered communities (Brown and Lowe l 974a, l 974b, 1980, 1994; Brown 1980, 1982). Because the classification system is both parallel and hierarchical (fig. l ), it is adaptable for use at various levels of detail. Mapping can be at any scale or unit of resolution. Moreover, the hierarchical sequence allows for the incorporation of existing vegetation classification taxa in use by federal, state, and private agencies into an appropriate biotic community level within the classification system (see, e.g., Nature Conservancy l 994a, l 994b, and Bourgeron et al. 1995) . The numerical coding of the hierarchy also makes the classification system computer compatible, thereby readily allowing for the storage and retrieval of information. The Brown, Lowe, and Pase (1979, 1980) system for the North American Southwest is currently in use in the RUN WILD program developed for use on remote terminals by the USDA Forest Service's Southwestern Region and Rocky Mountain Forest and Range Experiment Station (Patton 1978). This classification system is similarly incorporated within the files of the Arizona and New Mexico game and fish departments, and is used in environmental analysis procedures as required by the National Environmental Policy Act (e.g., Reichenbacher 1990). It was adopted by the Arid Ecosystems Resource Group of the U.S. Environmental Protection Agency for their Environmental Monitoring and Assessment Program (EMAP). This classification system facilitates biotic inventory and assessment, the delineation and stratification of habitats, resource r6 NORTH AMERICAN BIOTIC COMMUNITIES Biogeographic Realm \ \ Hydrologic Natural Upland Vegetation Regime 1st LEVEL Formation-Type 2nd LEVEL 3rd LEVEL Scrub Arctic- Cold Borcal Temperate Province Northeastern ij- Warm Temperate I ｓｩ･ｲ｡ｮＭｃｳ｣ＺｾＱＧ］ＰｧｯＡｊ＠ l'==P=la=ins====!J Biotic Community TropicalSubtropical --- --- --- / / / Biogeographic Cultivated Upland Vegetation Swamp and Riparian Swamp and Riparian Forest Clifnatic Zone Natural Wetland Vegetation Great Basin Interior Marshland 4th LEVEL Series Sth LEVEL Association 6th LEVEL Rush Series Sci1pus paludosus Association Saltgrass Series Sci1pus paludosus-lemna sp. Association Three-Square Series Scbpus americanus Association Potomogeton Sci1pus pa/udosusMixed Algae sp. Association Association Scilpus americanus- Figure r. Heirarchy of a bulrush marsh in Great Salt Lake, Utah, to the association (sixth) level of the classification system. planning, the interpretation of biological values, and other activities pertaining to natural history inquiry. It has proven especially useful for environmental analysis where the comparison of biological units is desired by governmental, scientific, educational, and other institutions. In short, the classification system is of particular use for those interested in inventorying biotic diversity for resource management, vegetation change, biological study, natural area preservation, and habitat acquisition. Moreover, because the system is hierarchical and universal, earlier inventory efforts can almost always be accommodated into it at some level. The ultimate value of any environmental classification system is the meaningful assignment of plant and animal habitats. Although most of the system's hierarchies are identified on the basis of observable vegetation , the inclusion of biogeographic realm, biotic province, and biotic community criteria automatically incorporates the less visible animal components into the classification. The system therefore allows for a more meaningful delineation and inventory of specific plant and animal habitats. For example, because bioticprovince criteria are included in the system, a resource manager can determine which marshlands are likely to include nesting black ducks (Anas rubripes) as opposed to similar-structured wetlands within other biotic provinces inhabited by Florida ducks (A. fulvigula ful- THE CLASSIFICATION SYSTEM vigula), mottled ducks (A. f maculosa), and Mexican ducks (A. platyrhynchos diazi). Such separations of plant and animal habitats are important in fulfilling the requirements of the Endangered Species Act, for evaluating the North American Waterfowl Plan, for monitoring warblers and other migratory birds of recent concern, and for following numerous other governmental directives. The inclusion of biogeographic criteria is also of primary importance in the world biosphere reserve program (see, e.g., Franklin 1977, McNeely and Miller 1983, Udvardy l984a, l984b, and IUCN 1974). The hierarchy is not rigorously systematic. Some of the equivalents at certain levels are greater in extent, and therefore importance, than others (e.g., at the fourth or biotic community level the Northeastern Deciduous Forest is much larger in area and far greater in importance than Rocky Mountain Alpine Tundra). But such anomalies are common in biological systematics; the variety and distribution of the Passeriformes are greater than in the Gaviiformes, even though both orders have equal rank within the class Aves. Although the hierarchy reflects scales, it is not scale dependent. For example, a lo-m 2 area of grass could be an interspace within Great Basin Conifer Woodland if the objective is a biotic community map at a scale of 1:125,000. This same area could also be Intermountain Grassland if one were sampling an association to be mapped at a scale of 1:15,625. Our purpose in presenting this classification system is neither to promote a new concept nor to replace existing classifications. Instead, we are attempting to present a hierarchical synthesis of the existing works on North American biogeography to aid in the development of a universal classification system for the world's natural environments. We recognize that portions of the classification system are dated or incomplete and require additional work. For example, climatic data are now available from a great variety of stations, and we are currently refining the temperature parameters of the climatic zones to make them more precise and meaningful. Also, the integrities of the various biotic community levels of the classification are presently testable through scientific methodologies, and we are now evaluating the "reality" of several biotic communities through a statistical analysis of seasonal climatological data. This analysis, and the recent acceleration in floristic and faunistic inventories, will help determine the reality of these and possibly other biotic communities. Presented below is a computer-compatible hierarchy of the world's biological systems with representative examples of the classification to the series (5th) level for North America. Neither the biotic community (4th) level, nor the series level examples of the classification are complete or final. Examples of the association (6th) level of the system are given only for the Rocky Mountain Montane Conifer Forest biotic community. Unlike previous presentations of the classification system (Brown and Lowe l974a, l974b; Brown, Lowe, and Pase 1979, 1980; Brown 1980), in which North America's biotic communities were all contained within the Nearctic biogeographical realm, the classification presented here properly separates the 18 NORTH AMERICAN BIOTIC CO MM UN ITIES 0 1,000. Nearctic ｾ＠ 3,000. Neotropical Figure 2. Biogeographic realms of North America. THE CLASSIFICATION SYSTEM continent into Nearctic and Neotropical realms (fig. 2). Remote offshore islands such as Mexico's Revilla Gigedo islands are considered as possessing distinctive biotic communities within an Oceanic realm. A description of each level of the classification system follows the outline below, where I,ooo = Biogeographic Realm I,roo = Hydrologic Regime I,I IO = Formation-type I,III =Climatic Zone I,III.I =Biotic Community (Regional Formation) I, I I r. I I = Series (Alliance of Generic Dominants) I,I I I.I I I =Association (Plant community of specific taxa) I,III.IIII =Plant and Animal Density, Plant Age Class, etc. The number preceding the comma (e.g., I,ooo) differentiates the hierarchy on the basis of the world's biogeographic realms (table I ). Origin and evolutionary history are thus recognized as being of primary importance in the determination and classification of biotic entities. The mappable reality of the world's biogeographical realms is, as in all natural taxonomy, interpretive and dependent on the criteria used . The following seven realms are adapted from Sclater (I 8 5 8 ), Wallace (I8 76), Allen (I892, I893), Sharpe (I893 ), Hesse, Allee, and Schmidt (I937), Darlington (I957), Dansereau (I957), Walter (I973), the International Union for Conservation of Nature and Natural Resources (IUCN I9 74), DeLaubenfels (I975), Cox, Healey, and Moore (I976), and Udvardy (I9 7p, I975b, I984a). I,ooo Nearctic-Continental North America exclusive of the tropics including most of the highland areas of Mexico and northern Central America (fig. 2) . 2,000 Palearctic-Eurasia exclusive of the tropics; Africa north of the Sahel. 3,000 Neotropical and Antarctican-South America, most of Mexico and Central America below an altitude of ca. I ,ooo meters, southern Florida, extreme southern Texas, and the Sonoran Desert region of California and Arizona (fig. 2). Also included here are New Zealand, the Falkland (Maldive) Islands, and other southern islands having an Arctic-Boreal (Antarctic-Austral) climatic regime and designated as belonging to the Antarctic Realm of Udvardy (I9 75a, I987). 4,000 Indomalayan (Oriental)-Southeast Asia, the Indian subcontinent, Indonesia, the Philippines, etc. 5,000 African (Afrotropical)-Africa south of the Sahara, and the southern portion of the Arabian peninsula. 6,ooo Australian-Australia and Tasmania. 7,000 Oceanic-Oceanic islands displaying a high degree of endemism, for example, the Hawaiian Islands, Madagascar, and New Guinea. Although the Oceanic or Oceanian realm designation 20 NORTH AMERICAN BIOTIC COMMUNITIES usually refers to the islands of the South Pacific (Udvardy 1996, unpubl. ms.), the term is used here more as a "catch-all" realm in that each pelagic island, or island group, has a distinctive evolutionary history that is more or less independent of continental influences. The assignation of the boundary between North America's Nearctic and Neotropical realms is not clear-cut and is, therefore, arbitrary in part. Even though the fauna of the Sonoran, Tamaulipan, and Floridian biotic provinces contains both Nearctic and Neotropical animals, the flora of these provinces is largely Neotropical. We have, therefore, included Sonoran Desertscrub, Tamaulipan Thornscrub, and Floridian Evergreen Forest in the Neotropical Realm. Conversely, biotic communities such as Veracruz and Guatemalan cloud forests, which possess a largely Nearctic flora, but an almost entirely Neotropical fauna, are here contained within the Nearctic Realm. Florida's "Everglades," possessing both a Nearctic and a Neotropical biota, but isolated by the waters surrounding the Florida peninsula, is classified tentatively here as a Nearctic Wetland. First Level The first digit after the comma (e.g., l,.I.oo) refers to one of four hydrologic regimes that include all upland (1,100) and wetland (1,200) communities existing under natural conditions. The important adaptations of plants and animals to terrestrial ecosystems, as opposed to wetland systems, are thus recognized early in the classification system. The classification of aquatic or submerged freshwater (e.g., l,300) and marine (e.g., l,400) environments is as yet in a tentative stage (see, e.g., Maxwell et al. 1994). Although accommodated in the system, the classification of these "open-water" communities is outside the scope of this work and is not included here. Also not included here, but included within the system, are terrestrial and wetland croplands and other human-maintained environments (Brown 1980). Because almost all "natural communities" are now more or less influenced by human activity, we include all native, naturalized, and adventive plant communities as belonging to either a natural upland or a natural wetland regime even though the vegetation may be in a successional, a man-altered, or even a disclimax condition (table l). In this classification system, wetlands include all periodically, seasonally, or continually submerged lands populated by emergent plants and life-forms different from the immediately adjacent upland vegetation (see also, e.g., Martin et al. 1953, Lowe 1964, and Cowardin et al. 1979). Hence, riparian communities containing both upland and wetland components are included here in the natural wetland regime (e.g., l,200, table l) . Second Level The second digit after the comma, (e.g., l,1.I.o) refers to one of the following recognized plant formations, or, as they are called on a worldwide basis, formation-types (table 2, fig . 3). Formation-types are vegetative responses to integrated environmental factors, most importantly, available soil moisture. THE CLASS IFI CATION SYSTEM 21 Table 1. Summary of the world's natural vegetation to the first level Hydrologic Regime Biogeographic Realm 1,000 2,000 3,000 4,000 5,000 6,000 7,000 Natural Upland Vegetation Nearctic Palearctic Neotropical-Antarctican lndomalayan (Oriental) African (Afrotropical) Australian Oceanic Natural Wetland Vegetation 1,200 2,200 3,200 4,200 5,200 6,200 7,200 1, 100 2,100 3,100 4,100 5,100 6,100 7,100 Table 2. Summary for the natural upland and wetland vegetation of the world to the second level Formation-type Biogeographic Realm UPLAND 1,100 Nearctic 2,100 Palearctic 3,100 Neotropical-Antarctican 4,100 lndomalayan (Oriental) 5,100 African (Afrotropical) 6,100 Australian 7,100 Oceanic WETLAND 1,200 Nearctic 2,200 Palearctic 3,200 Neotropical-Antarctican 4,200 lndomalayan (Oriental) 5,200 African (Afrotropical) 6,200 Australian 7,200 Oceanic Tundra Forest and Woodland Scrubland Grassland Desertland 1,110 2,110 3,110 4,110 5,110 6,110 7,110 1,120 2,120 3,120 4,120 5,120 6,120 7,120 1,130 2,130 3,130 4,130 5,130 6,130 7,130 1,140 2,140 3,140 4,140 5,140 6, 140 7,140 1,150 2,150 3,150 4,150 5,150 6,150 7,150 Wet Tundra Forest* Swamp Scrub Marshland 1,210 2,210 3,2 10 4,210 5,210 6,210 7,210 1,220 2,220 3,220 4,220 5,220 6,220 7,220 1,230 2,230 3,230 4,230 5,230 6,230 7,230 1,240 2,240 3,240 4,240 5,240 6,240 7,240 Strand 1,250 2,250 3,250 4,250 5,250 6,250 7,250 NonVegetated 1,160 2,160 3,160 4,160 5,160 6,160 7,160 NonVegetated 1,260 2,260 3,260 4,260 5,260 6,260 7,260 *Swamp forests, bog forests, and riparian forests. Upland (Terrestrial) Formations Tundra-Arctic and alpine communities existing in an environment so cold that moisture is unavailable during most of the year, precluding the establishment of trees, and in which the maximum vegetative development is perennial herbaceous plants, shrubs, lichens, and mosses, with grasses poorly represented or at least not dominant. We nonetheless recognize that the holistic integrity of a "tundra" formation-type is open to serious question. Tundra may also be treated as composed of scrublands, grasslands, desertlands, and marshlands (wet-tundra) existing in an Arctic-Boreal climatic zone (Billings and Mooney 1968; Billings 19 73). Alpine tundra communities in the Neotropics are known as Paramos. NORTH AMERICAN BIOTIC COMMUNITIES 22 0 10. Tundras lillll 20. Forests and Woodlands 11111 30. Scrublands and Swmnp • 40. Grasslands and Marshlands 0 so. Ill 60. Deserts Non-vegetated Figure 3. Plant formations of North America. THE CLASSIFICATION SYSTEM Forest and Woodland- Communities dominated principally by trees actually or potentially more than ten meters in height, and characterized by closed and/or multi-layered canopies (forests); or, communities comprised principally of trees with a mean actual or potential height usually less than ten meters, the canopy of which is open, interrupted, and singularly layered (woodland). The "savanna" formation-type of some biogeographers (e.g., Beard 1953; Dyksterhuis 1957) is here recognized as a grassland. We follow the UNESCO classification system in which savannas are areas having an almost continual grass cover, and in which trees may form up to 30 percent of the plant cover (Mueller-Dombois and Ellenberg 1974). "Parklands," mosaics of grassland and smaller or larger stands of trees or shrubs, are considered as being represented by two or more distinct formation-types. Scrubland-Communities dominated by shrubs and/or multistemmed trees generally not exceeding ten meters in height, often possessing microphyll or sclerophyll leaves, usually presenting a closed physiognomy, or, if open, interspaced with low-structured perennials. Grassland- Communities dominated actually or potentially by grasses and/or other herbaceous plants. Desertland- Communities in an arid environment (usually less than 300 millimeters precipitation per annum) in which more than 50 percent of the ground can be expected to lack vegetative cover. Wetland Formations Wet Tundra- Wetland communities existing in an environment so cold that plant moisture is unavailable during most of the year, precluding the establishment of trees and all but a low herbaceous plant structure in a hydric matrix. Wet tundra may also be treated as swampscrub, marshland, or strand communities within an ArcticBoreal climatic zone. Swamp and Riparian Forest- Wetland communities possessing an overstory of trees potentially more than ten meters in height and frequently characterized by closed and/or multi-layered canopies. Swamp and Riparian Scrub- Wetland communities dominated by short trees and/or woody shrubs, generally under ten meters in height and usually presenting a closed physiognomy. Marshland- Wetland communities in which the principal emergent plant cover consists of herbaceous emergents having their basal portions annually, periodically, or continually submerged. Strand- Beach and river channel communities subject to regular to infrequent submersion, wind-driven waves, or spray. Plants are separated by significant areas devoid of perennial vegetation and the vegetative cover is usually less than 50 percent. Some upland and wetland communities, e.g., dunes, lava flows, glaciers, salt lakes, etc., are essentially without vegetation. For purposes of classification, such areas can be considered as belonging to a nonvegetated or a "nonvascular plant formation" if a desertland or strand formation-type is considered inappropriate (table 2) . 24 NORTH AMERICAN BIOTIC COMMUNITIES Third Level The third digit beyond the comma (e.g., l,1 r_r_) refers to one of the four world climatic zones (see, e.g., Walter 1973, Ray 1975, and Cox, Healey, and Moore 1976) in which minimum temperatures are recognized as a major evolutionary control of and within formation types (table 3, fig. 4). Arctic-Boreal (Antarctic-Austral)- Lengthy periods of freezing temperatures with the coldest month isotherm -3°C. (Koppen 1931); growing season generally averaging less than loo days, occasionally interrupted by nights of below-freezing temperatures. Cold Temperate-Freezing temperatures usually of moderate duration, although of frequent occurrence during winter months. Potential growing season generally from l oo to 200 days and confined to late spring and summer when freezing temperatures are infrequent or absent. Warm Temperate-Freezing temperatures of short duration but generally occurring every year during winter months. Potential growing season more than 200 days with less than an average of 150 days a year subject to temperatures below 0°C. or chilling fogs. Tropical-Subtropical-Infrequent or no twenty-four-hour periods of fre ezing temperatures, cold fogs, or chilling winds . Fourth Level The fourth digit after the comma (e.g., l,II I.1..) refers to a regional formation within a biotic province. Each of these biotic communities comes with a name that describes the formation's ecological center and/or one of its most distinguishing physiographic features, e.g., "Chihuahuan Desertscrub." These names in turn are derived from the biotic province in which the biotic community is found . Also called biogeographic regions, biotic provinces are areas characterized by a particular precipitation pattern or other climatic regimen so that the plant and animal species found therein share a more or less similar environment (Vestal 191 4; Ruthven 1920; Clements and Shelford 1939; Pitelka 1941; Dice 1943; Odum 1945; Goldman and Moore 1945; Blair 19 50; Webb 19 50; Miller 1951; Kendeigh 19 52; Ryan 1963; Lowe 1964; Aldrich 1967; Franklin 19 77; and, most recently, Udvardy l975a, l9 75b, l984a, l984b). As used here, biotic provinces are regional areas having a distinctive recent evolutionary history and hence a more or less characteristic biota at the species and subspecies levels. Similar regions classified solely on the basis of vegetation or fauna are called phytogeographic and faunistic provinces respectively (Lowe 1964). Composed of one or more formation-classes, biotic provinces can be subdivided into districts (Dice 1943; Blair 1950) as well as into biotic communities (Brown 198 2). The "Ecoregion" and "Ecosystem" classifications recently proposed for the United States and Canada (see, e.g., Bailey and Cushwa 1981, Wiken, Rubec, and Ironside 1989, Demarchi 1993, and Ricketts et al. 1997), while based more on geographic criteria than on evolutionary considerations, are roughly analogous to biotic provinces. Their respective "province" and "ecoprovince" levels are more similar, however, to biotic districts than to biotic communities. THE C LASSIFICATION SYS T EM 25 Table 3. Summary tor the natural upland and wetland vegetation of Nearctic and Neotropical North America to the third level Climatic (thermal) Zone Arctic-Boreal Antarctic-Austral Formation-type Cold Temperate Warm Temperate TropicalSubtropical NEARCTIC Upland 1, 110 1,120 1,130 1,140 1, 150 1, 160 Tundra Forest and Woodland Scrubland Grassland Desertland Nonvegetated Wetland 1,210 Wet Tundra 1,220 Swamp and Riparian Forests Swamp and Riparian Scrublands 1,230 Marshland 1,240 Strand 1,250 Nonvegetated 1,260 1'111 1,121 1, 131 1, 141 1,151 1, 161 1, 122 1,132 1,142 1,152 1, 162 1,123 1, 133 1, 143 1, 153 1, 163 1, 124 1, 134 1,144 1,154 1,164 1,211 1,221 1,23 1 1,241 1,251 1,261 1,222 1,232 1,242 1,252 1,262 1,223 1,233 1,243 1,253 1,263 1,224 1,234 1,244 1,254 1,264 3, 111 3, 121 3, 131 3,141 3,151 3, 161 3,122 3,132 3,142 3,152 3,162 3,123 3,133 3,143 3,153 3,163 3,124 3,134 3,144 3,154 3,164 3,211 3,221 3,231 3,241 3,251 3,261 3,222 3,232 3,242 3,252 3,262 3,223 3,233 3,243 3,253 3,263 3,224 3,234 3,244 3,254 3,264 NEOTROPICAL Upland 3, 110 3,120 3,130 3,140 3,150 3,160 Tundra and Paramo Forest and Woodland Scrubland Grassland Desertland and Puna Nonvegetated Wetland Wet Tundra 3,210 3,220 Swamp and Riparian Forests Swamp and Riparian Scrublands 3,230 Marshland 3,240 Strand 3,250 Nonvegetated 3,260 Some biotic provinces and biotic communities have long been recogni zed by ecologists, and their designations, if not their boundaries, are widely accepted, for example, the Sonoran Desert (Shreve 1942, 19 51; MacMahon 1988), Plains Grassland (Weaver and Clements 1938; Sims 1988), Californi a Chaparral (Munz and Keck 1949, 19 50), Arctic Tundra (Bliss 198 8), and Northeastern Deciduous Forest (Braun 19 50; Greller 1988). Others, for example, Alaskan Tundra (Shelford 1963; Ricketts et al. 1997), Madrean Evergreen Woodland (Lowe 1964; Brown 1982), and Sinaloan Deciduous Forest (Gentry 1982), are in the process of being adopted. Still other communities, including those in the Guatema lan, Veracruz, and Yucatan biotic provinces, have yet to be accepted or adequately tested . NORTH AMERICAN BIOTI C CO MMUNITIES 0 1. Arctic-Boreal D 2. Cold Temperate IJ!ll 3. Warm Temperate • 4. Tropical-Subtropical Figure 4. Climatic zones of North America. TH E CLASSIFI CATIO N SYSTEM The biotic provinces shown m figure 5 are modifications and refinements of those proposed by Goldman and Moore ( l 94 5 ), Ryan (1963), Udvardy (1975a, l975b), and others, and neither their terminology nor their boundaries are intended to be final. The following descriptions for the provinces of the Nearctic Realm are therefore tentative, and intended solely to facilitate the completion of the classification system: Polar (e.g., Polar Tundra, Polar Wetlands, etc.): This is essentially the high-arctic region of Bliss (1988) and other ecologists, and consists of those regions lying mostly above 72 degrees N latitude and characterized by an extremely harsh climate, low precipitation, and more or less continuous permafrost. Alaskan-Yukon (e.g., Alaskan Tundra, Alaska-Yukon Subarctic Conifer Forest, Alaskan Swamp Scrub, Alaskan Wet Tundra, etc.): Northern and western coastal Alaska, interior Alaska, and most of Yukon Territory (the "Alaskan Tundra" and "Yukon Taiga" of Udvardy l97p, l975b). Canadian (e.g., Canadian Tundra, Canadian Taiga, Canadian Marshland, etc.): Boreal Canada and the northeastern United States south of the High-Arctic and the Alaska-Yukon biotic provinces, including a number of offshore islands. The mean annual growing season is less than roo days and most of the precipitation falls as snow. Udvardy's (1975a, l975b) "Canadian Taiga" and "Canadian Tundra." Arctic-Alpine (e.g., Arctic-Alpine Tundra): Mountainous areas above timberline that lie within and adjacent to the Alaskan-Yukon and Canadian biotic provinces. Greenlandian (e.g., Greenlandian Coastal Tundra, Greenlandian Wet Tundra, etc.): Coastal Greenland and offshore islands not covered by ice and not subject to permafrost (see also Udvardy l97p, l975b). Rocky Mountain (e.g., Rocky Mountain Alpine Tundra, Rocky Mountain Subalpine Conifer Forest, Rocky Mountain Montane Conifer Forest, Rocky Mountain Montane Meadow, Rocky Mountain Riparian Deciduous Forest, etc.) : The Rocky Mountain cordillera from British Columbia southward to the higher elevations of the Chiricahua Mountains in Arizona. Also included here are the upper elevations of those mountains within the Great Basin biotic province (see also, e.g., Udvardy l975a, l975b, and Peet 1988). Cascade-Sierran (e.g., Cascade-Sierran Alpine Tundra, CascadeSierran Subalpine Conifer Forest, Cascade-Sierran Montane Conifer Forest, Cascade-Sierran Montane Chaparral, etc.): Communities residing in the higher elevations of the Cascade and Sierra Nevada mountain cordillera from British Columbia southward through the Sierra Nevada and the Transverse and Peninsular ranges to the Sierra San Pedro de Martir in Baja California Norte (see also Udvardy l97p, l975b). Adirondack-Appalachian (e.g., Adirondack-Appalachian Alpine Tundra, Adirondack-Appalachian Subalpine Conifer Forest, etc.): High-elevation communities in the Adirondack and Appalachian NO RTH AMERICAN BIOTIC CO MMU N ITIES 0 D IS! D D D •• 1. Polar 2. Greenlandian 3. 4. D IS! 8. Rocky Mountains 9. Great Basin [ii 10. Cascade-Sierran Alaskan Canadian Ill 11. Sitkan Northeastern 1!1\11 12. Oregonian Appalachian 13. California 5. 6. 7. Plains • II 14. Mohave D 15. Chihuahuan ED 16. 17. 18. 19. D • D D II [ii 22. 23. Madrean D 24. Transvolcanic 25. Gulf Coast D 26. 20. Guatemalan D 27. 21. Central American II 28. Southeastern • • Veracruz Ill D Guerreran Nayarit Ill Campechian Sinaloan Sono ran San Lucan Figure 5. A generalized map of the biotic provinces of North America. • 29. Tamaulipan 30. Yucatan 31. Florida 32. Caribbean THE CLASSIFI CATION SYSTEM mountain cordillera from Maine and New Brunswick southward to the Great Smoky Mountains in Tennessee and North Carolina. Transvolcanic (e.g., Transvolcanic Alpine Tundra, Transvolcanic Subalpine Conifer Scrubland, Transvolcanic Subalpine Grassland, etc): Those high-elevation communities along the Eje Volcano cordillera of Central Mexico-the "Transverse Volcanic" biotic province of Goldman and Moore (1945). Northeastern (e.g., Northeastern Deciduous Forest, Northeastern Maritime Marshland, etc.): The cold temperate and summer wet "Eastern Deciduous Forest" of Braun (1950) and Greller (1988) minus the Mixed Deciduous and Evergreen Forest region in the warm-temperate southeastern United States. The "Eastern Forest" of Udvardy (1975a, l975b). Sitka Coastal (e.g., Sitkan Coastal Conifer Forest, Sitkan Coastal Strand, etc.): Those rain- and fog-drenched communities in the cismontane region of the Pacific coast from the vicinity of Vancouver Island northwestward to southern Alaska. The "Sitkan" biotic province of Dice (1943); the "Sitkan" biogeographical province of Udvardy (1975a, l975b). Oregonian (e.g., Oregonian Coastal Conifer Forest, Oregonian Deciduous and Evergreen Forest, Coastal Grassland, Oregonian Maritime Marshland, etc.): Cismontane communities occurring between the Pacific Coast and the Cascade and coast ranges from the vicinity of Vancouver Island southward to the San Francisco Bay region of central California, and locally, southward. The "Oregonian" biotic province of Dice (1943) and the "Oregonian" biogeographical province of Udvardy (1975a, l975b). Great Basin, or Intermountain (e.g., Great Basin Conifer Woodland, Great Basin Montane Scrub, Great Basin Shrub-Grassland, Great Basin Interior Marshland, etc.): Those relatively highelevation intermountain communities between the Rocky Mountain and Cascade-Sierran cordi lleras. The "Artemisian," "Palusian," and "Navahonian" biotic communities of Dice (1943); Udvardy's (1975a, l975b) "Great Basin" biogeographic province. Plains (e.g., Plains Grassland, Plains Interior Marshland, etc.): Those cold-temperate communities lying west of the Northeastern Deciduous Forest, east of the Rocky Mountain cordillera, and south of the Canadian Taiga. The northern portions of Udvardy's (1975a, l975b) "Grasslands" biogeographic province. Southeastern (e.g., Southeastern Deciduous and Evergreen Forest, Southeastern Maritime Scrubland, Southeastern Riparian Forest, etc.): Those mostly forested warm-temperate communities south and southeast of the cold-temperate Northeastern Deciduous Forest exclusive of the Texas and western Louisiana Gulf Coast and those tropical communities peculiar to extreme southern Florida. Braun's (1950) "Southeastern Evergreen Forest" region, Dice's (1943) "Austroriparian" biotic province, Udvardy's (197p, l975b) "Austroriparian" biogeographic province, and Christensen's ( l 9 8 8) "Southeastern Coastal Plain." 30 N ORTH AMERICAN BIOTI C COMMUNITIES Gulf Coastal (e.g., Gulf Coastal Grassland, Gulf Coastal Maritime Marshland): Those open, or formerly open, grassland and wetland communities found along the Texas and western Louisiana coasts. Tharp's (1939) "Coastal Prairie." California (e.g., California Evergreen Forest and Woodland, California Chaparral, California Coastalscrub, California Valley Grassland, California Interior Marshland, etc.): Those warm-temperate, winter-rainfall communities west of the Sierra Nevada and Peninsula ranges, south and east of the Oregonian biotic province's coastal forests, and north of the Sonoran Desert in Baja California Norte. The "Californian" biotic province of Dice (1943), Udvardy (1975a, 1975b), and other authors. Madrean (e .g., Madrean Montane Conifer Forest, Madrean Montane Meadow, Madrean Evergreen Woodland, etc.): Those moderate- to high-elevation communities found in the mountains and foothills of the Sierra Madre Oriental, the Sierra Madre Occidental, and their outliers (Brown 1982). The "Sierra Madre Occidental" and "Sierra Madre Oriental" biotic provinces of Goldman and Moore (1945) and the northern portions of Udvardy's (1975a, l 97 5 b) "Madrean-Cordilleran" biogeogra phic province. Guerreran (e.g., Guerreran Evergreen Forest and Woodland). Temperate communities at moderate to high elevations in the Sierra Madre de! Sur and other mountain ranges south of the Rio Balsas and west of the Isthmus of Tehuantepec. The "Sierra Madre de! Sur" biotic province of Goldman and Moore (1945); portions of Udvardy's (1975a, 1975b) "Madrean-Cordilleran" biogeographic provmce. Guatemalan (e.g., Guatemalan Montane Conifer Forest, Guatemalan Evergreen Forest and Woodland): Those temperate and moderate- to high-elevation communities east of the Isthmus of Tehuantepec in Chiapas, Mexico; Guatemala; Honduras; and northern Nicaragua. Goldman and Moore's (1945) "Chiapas Highlands" and Ryan's (1963) "Chiapas-Guatemala Altos," "LempiraTegucigalpan," and "Nicaraguan Montane" biotic provinces. The southern portion of Udvardy's (1975a, 1975b) "MadreanCordilleran" biogeographic province. Veracruz (e.g., Veracruz Cloud Forest): Wet, warm-temperate hardwood forest communities found at moderate to high elevations east of the crest of the Sierra Madre Oriental and north of the Transvolcanic mountain ranges (see, e.g., Martin 1958). San Lucan (e.g., San Lucan Evergreen Forest and Woodland): Those temperate communities in the Sierra de la Laguna and adjacent mountain ranges in the Cape region of Baja California Sur (Arriaga and Ortega 1988) . The higher elevations of Dice's (1943) "San Lucan" biotic province. Chihuahuan, or Semidesert (e.g., Chihuahuan Desertscrub, Chihuahuan Interior Chaparral, Semidesert Grassland, Chihua huan Interior Marshland, etc.): Those arid and semi-arid communities on the Mexican Plateau between the Sierra Madre Oriental and the Sierra Madre Occidental, and north of the Eje Volcanoes. The northern THE CLASSIF!CATION SYSTEM boundaries are less determinate but extend into west Texas, southern New Mexico, and southeastern Arizona (Shreve 1942; Udvardy l975a, l975b; Morafka 1977; Brown 1982). This biotic province contains most of the "Chihuahuan" and "Apachian" biotic provinces of Dice (1943). Mohave (e.g., Mohave Desertscrub, Mohave Interior Strand, etc.): Those warm-temperate communities lying within the boundaries of the Mohave Desert (Shreve 1942; Turner 198 2; Brown and Lowe 1980, 1994). Dice's (1943) "Mohavian" biotic province. Southwestern Interior, or Arizona (e.g., Southwestern Interior Chaparral, Southwestern Riparian Deciduous Forest, etc.): Those warm-temperate and biseasonal-rainfall communities in subMogollon Arizona and extreme western New Mexico north and east of the Sonoran Desert. Portions of Dice's (1943) "Navahonian," "Apachian," and "Sonora" biotic provinces. Further consideration may place these largely chaparral, grassland, and riparian communities within the Chihuahuan (Semidesert) biotic province (see, e.g., Brown 1982). We have adopted the following biotic provinces in North America as occurring within the Neotropical Realm: Central American (e.g., Central American Paramo, Central American Cloud Forest, Central American Evergreen Rain Forest, Central American Semi-evergreen Forest, Central American Dry (Monsoon) Forest, Central American Savanna Grassland, Central American Thornscrub, etc.): Panama, Costa Rica, El Salvador, and tropical Honduras and Nicaragua south of the Gulf of Honduras and below the Guatemalan highlands. Ryan's (1963 ) "Col6nDarien," "Guatuso-Talmanacan," "Chinandegan," "Mosquito," and "Escuinta-Usulutan " biotic provinces. Udvardy's (1975a, l975b) "Panamanian" and "Central American" biogeographic provmces. Campechian (e.g., Campechian Semi-Evergreen Forest, Campechian Montane Evergreen Forest). The wet-tropic areas of southern Mexico, Guatemala, and Belize east of the Isthmus of Tehuantepec and below the Chiapas-Guatemalan highlands northward to the southern half of the Yucatan Peninsula. The southern portion of Goldman and Moore's (1945) and Ryan 's (1963) "Yucatan Peninsula" biotic province; the southern half of Udvardy's (l 97 sa, l 97 5 b) "Campechian" biogeographic province. Yucatan (e.g., Yucatan Semi-Deciduous Forest, Yucatan Dry Deciduous Forest, Yucatan Maritime Scrubland, etc.): The arid northern portions of the Yucatan Peninsula. The northern portion of the "Yucatan Peninsula " biotic province of Goldman and Moore (1945) and Udvardy's (1975a, l975b) "Yucatecan" biogeographic province. Guerreran, or Nayarit-Guerreran (e.g., Guerreran Dry Deciduous Forest, Guerreran Thornscrub, Nayarit-Guerreran Semi-Evergreen Forest, etc.): Those arid and semi-arid tropical valley and foothill communities occurring southward from Mexico's transverse volcanic ranges to the Isthmus of Tehuantepec and into the interior valleys of 32 NORTH AMERICAN BIOTI C COMMUN ITIES Chiapas and Guatemala. This biotic province is essentially an expansion of the "Nayarit-Guerrero" biotic province of Goldman and Moore (1945) and is analogous to the "Guerreran" biogeographic province of Udvardy (1975a, l975b). Veracruz (e.g., Veracruz Evergreen Rain Forest, Veracruz SemiEvergreen Forest, etc). Tropical and subtropical Mexico east of the Sierra Madre Oriental from the vicinity of Tampico south to the lowlands surrounding the northern portion of the Isthmus of Tehuantepec. The "Veracruz" biotic province of Goldman and Moore (1945). Tamaulipan (e.g., Tamaulipan Semi-Deciduous Forest, Tamaulipan Thornscrub, Tamaulipan Coastal Strand, etc.): Those semi-arid subtropical and tropical communities found in southern Texas and northeastern Mexico southward to the vicinity of Tampico. The "Tamaulipan" biotic province of Dice (1943), Goldman and Moore (1945), Muller (1947), Martin (1958), and others. Sinaloan (e.g, Sinaloan Dry Deciduous Forest, Sinaloan Tbornscrub, Sinaloan Maritime Scrub, etc.): Those semi-arid subtropical and tropical communities west of the Sierra Madre Occidental and south and southeast of the Sonoran Desert from northeastern Sonora southward to the vicinity of Puerta Vallarta and the Transverse volcanic ranges. This province includes Shreve's (1951) "Footh ill s of Sonora" subdivision of the Sonoran Desert, Gentry's (1942, 1982) "Sinaloan Deciduous Forest," Goldman and Moore's (1945) "Sinaloa" biotic province, and the mainland portion of Udvardy's (1975a, l975b) "Sinaloan" biogeographic province. Sonoran (e.g., Sonoran Desertscrub, Sonoran Savanna Grass land, Sonoran Oasis Forests, etc.): Those communities conta ined within Shreve's (1942, 1951) boundaries of the Sonoran Desert in southeast California, Baja California, Arizona, and Sonora, save for his "Foothills of Sonora" subdivision. The "Sonora" biotic province of Goldman and Moore (1945) and the "Sonoran" biogeographic province of Udvardy (1975a, l975 b). San Lucan (e.g., San Lucan Dry Deciduous Forest, San Lucan Thornscrub, etc.): The tropical and semi-arid portion of the Baja California Peninsula that is not Sonoran Desertscrub (see, e.g., Shreve 1951). The southern reaches of Dice's (1943) "San Lucan" biotic province and Goldman and Moore's (1945) "Southern Baja California" biotic province. The Baja Peninsular portion of Udvardy's (1975a, l975b) "Sinaloan" biogeographic province. Floridian (e.g., Floridian Evergreen [Hammock] Forest, Floridian Freshwater Marshland, Floridian Maritime Swamp Scrub, etc.): The southern extremity of the Florida Peninsula including the Florida Keys and adjacent waters. Portions of Udvardy's (1975a, l975b) "Everglades" biogeographic province. Caribbean (e.g., Caribbean Cloud and Montane Evergreen Forests, Caribbean Lowland Evergreen and Semi-evergreen Forest, Caribbean Dry Forest, Caribbean Thornscrub, Caribbean Savanna Grassland, Caribbean Coasta l Strand, etc.): The West Indies including all of the islands of the Caribbean Sea north of Trinidad and Tobago. Further consideration may warrant the division of this THE CLASSIFICATION SYSTEM biotic province into "Cuban," "Greater Antillean," and "Lesser Antillean" provinces as delineated by Udvardy (1975a, l975b). In the western United States, in Mexico, and in Central America, where the topographic relief is pronounced, climatic change and other ecologically isolating factors are more complex. Biotic communities in these areas therefore tend to diminish in size and increase in number. Their boundaries, following certain topographical features, may be sharply defined or highly complicated (Udvardy 1969). Even though the recognition of biotic communities will always be interpretive in part, their boundaries can be delineated by assigning communities of plant dominants and their associates (fifth level of the classification system) to the biotic province in which these species are characteristic taxa. Biotic communities are characterized by distinctive plants and animals living within a formation-type (second level of the classification system) that are commonly called "indicator species" (Merriam and Stejneger 1890; Clements 1920; Shelford 1963). Because each biotic community is a complete ecosystem of plants, animals, and their habitats, this level is the natural unit for studying the interrelations of plant and animal species (Odum 1945; Shelford 1945; Kendeigh 1952). Although the original concept of "ecosystems" involved the exchange of chemical energy within a given community (Odum 1945), this term, as it is often presently used, is equivalent to a biotic community (see, e.g., MacKinnon et al. 1992). The reality of biotic communities as ecological units of regional isolation can be tested statistically through the analysis of climatic data and the presence (or absence) of endemics, as is presently being done for the San Lucan Dry Deciduous Forest by Breceda et al. (1994). Each biotic community is analogous to a "small biome" in the biome hierarchy of Allen and Hoekstra (1992), in which vegetation can be seen as an exemplar of a community that contains both plants and animals. Viewed thus, plants and animals not only are members of a species, they are interacting members of a community. But, because they are composed of individual members, a biotic community is not in a progression toward stability in the Clementian sense, but is instead a complex that is subject to change with shifts in climate, the occurrence of "creative catastrophes" such as fire and hurricanes, and variations in animal numbers and pressures (Holling 1995). For these reasons, biotic communities may alter between cycles of forest and grassland, or shru bland and grassland, each species evolving both independently and dependently of the community as a whole. Moreover, some communities will grow in size, while others shrink in extent (Betancourt, Van Devender, and Martin 1990; McClaran and Van Devender 1995). The result is a change in not only the community's plants and animals, but in the biotic community itself, some biotic communities disappearing while newer ones evolve. Other biotic communities may retain their basic integrity even though a number of their principal constituents become extinct (see, e.g., Graham et al. 1996). 33 NORTH AMERICAN BIOTIC COMMUNITIES 34 A complication frequently overlooked is that most biotic provinces contain more than one formation-type and hence more than one biotic community. For example, one can find grassland "savannas" within the Southeastern Deciduous and Evergreen Forest and "elfin" woodlands and "krumholtz" scrublands above tropical montane forests and subalpine forests. Although minor in extent, these often edaphic-controlled or otherwise limited communities have a distinctive evolutionary history and may justifiably be considered as biotic communities in their own right. The fourth (biotic community) and fifth (series) levels have been most often used to map regions, states, and countries (e.g., Bruner 1931; Rasmussen 1941; Hayward 1948; Webb 1950; Allred, Beck, and Jorgensen 1963; Aldrich 1967; Kuchler 1964, 1977; Franklin and Dyrness 1973; Brown 1973; Brown and Lowe 1980, 1994). Biotic provinces and biotic communities are also the bases for biosphere reserve programs in the United States and elsewhere (IUCN 1974, 1992; Franklin 1977; Udvardy l984b). Tables 4 and 5 list and illustrate those biotic communities shown on the 1:10,000,000 color map as well as a few others too minor in extent to depict. Present plans are to describe each of these biotic communities in a publication similar to one for the southwestern United States and northwestern Mexico (Brown 1982). Neither the classification nor the map is meant to be final. Additional biotic communities may be identified and some of those listed may be discarded upon further analysis and consideration. Fifth Level The fifth digit beyond the comma (e.g., l,11r.1i) provides the principal plant-animal series within the biotic communities, each recognized by one or more indicator plants. These general series of actual or potential plant dominants, sometimes referred to as covertypes (Society of American Foresters 1954) or "alliances" (Nature Conservancy l994a), are in turn composed of one or more plant associations (Oosting 1956; Lowe 1964; Braun 1950; Franklin and Dyrness 1973; Pfister et al. 1977). For example, a yellow-pine series would include all plant associations within a biotic community in which Pinus ponderosa is, or can be assumed to become, a dominant component (table 4). Because the number of series within any given biotic community may be large, and because some biotic communities are as yet little studied and imperfectly known, only illustrative examples of the fifth level are given for the biotic communities listed in tables 4 and 5. For these same reasons, the numerical prefix given for a particular series is also illustrative and may be modified at will. It should be noted that tropical and subtropical series are inherently more diverse than those in arctic-boreal and temperate biotic communities. Series in tropical and subtropical biotic communities frequently contain dozens if not hundreds of competing species of plants and animals per unit area. Arctic-boreal series typically contain only one or two plant dominants. Series in arctic-boreal and temperate environments also tend to be THE CLASSIFICATION SYSTEM larger in extent and fewer in number than those in the tropics. For these reasons the identification and classification of fifth-level communities tend to be more specific in Canada and the United States than in Mexico or Central America (compare, for example, the vegetative classifications of Halliday 1937, Kuchler 1964, Braun 1950, and Franklin and Dyrness 1973, with those of Tosi 1969 and Rzedowski 1978). Some plant dominants are highly facultative (able to live under more than one set of conditions in various growth forms), and the same species may be dominant in more than one formation -type. As an extreme example, mesquite (Prosopis juliflora) may be the dominant life-form in forest and woodland, scrubland, desertland, and even disclimax grassland formations. The distributions of some plant dominants also span more than one climatic zone, for example, mesquite, creosote-bush (Larrea tridentata), and the introduced saltcedar (Tamarix parviflora). The plant and animal associates of these sometime-dominants usually differ, however, when passing from one formation-type or climatic zone to another. Some generic dominants may also occur in more than one biotic community (e.g., Larrea, Populus, Salix, Quercus, etc.) . Nonetheless, further investigation should show a significant change in plant and animal associates when passing from one biotic community to another. Furthermore, when the same species is present in more than one biotic community, the different populations can be expected to exhibit genetic and other differences as was demonstrated by Yang (1970) for Larrea tridentata in the Chihuahuan, Sonoran, and Mohave deserts. Sixth Level The sixth digit after the comma (e.g., l,11r.11i) refers to a distinctive association. An association has been defined by the International Botanical Congress in l9IO as a plant community having a particular floristic composition, uniform habitat conditions, and uniform physiognomy (see also, e.g., Braun-Blanquet 193 2). Plant associations are therefore more or less local in distribution, and, as used here, generally equiva lent to niches (Pitelka 1941) or habitat-types as outlined by Daubenmire and Daubenmire (1968), Layser (1974), and Pfister et al. (1977). Although we provide plant-association examples for two fifth-level series within one fourth-level biotic community (Douglas-fir and Yellow Pine series within Rocky Mountain Montane Conifer Forest), the enormous numbers of possible sets preclude presentation for the continental treatments in tables 4 and 5. The number of plant associations may therefore be expanded to accommodate regional studies. This level of the classification system emphasizes existing vegetation. As a working system, it accommodates, but does not stress, both subclimax and disclimax plant associations as well as potential (prevailing) natural vegetation (see, e.g., Clements 1916, Weaver and Clements 1938, Clements and Shelford 1939, Oosting 1956, Kuchler 1964, Shreve 1951, and Whittaker 1978) . Those plant associations judged to be subclimax or seral in nature can be indicated by an "s" 35 NO RT H AM ERI C AN BIOTIC C O MMUN IT IES as a superscript above the numerical code, e.g. III. III ' . Similarly, those series and associations considered to be in a disclimax or a more or less permanent man-altered condition can be indicated by a " D " at the series (fifth ) level or a " d" at the plant association level. Seventh Level The seventh digit after the comma (e.g. , I,III.III_!_ ) acco mmodates detailed assess ment of composition, stru cture, density, or other qu antitative determinations fo r plant and animal species within a plant association. Implementati on of thi s level in the system is intend ed for intensive studies of limited areas or "stands" (e.g., DickPeddie and Mo ir I97 0). N o exa mpl es are th erefore pro vided in ta bles 4 and 5. Table 4. Nomenclature of upland biotic communities for Nearctic and Neotropical North America The biotic communities (fourth level) are presented on the 1:10,000,000 color map. Some series (fifth level) and association (sixth level) examples are provided here for demonstration purposes and indicated by an asterisk (*). A plus sign (+) indicates biotic communities for which our incomplete knowledge precludes presentation of representative series and association examples. 1,000. NEARCTIC REALM 1,100. Natural Upland Vegetation 1, 110. Tundra Formation 1, 111 . Arctic and Alpine Tundra 1,111 .1 Polar (High Arctic) Tundra (plate 1) 1,111 .11 Sedge-Moss Series* 1, 111 .12 Cushion Plant-Lichen Series* 1,111 .2 Alaskan Tundra (plate 2) 1,111 .3 Canadian (Low Arctic) Tundra (plate 3) 1,111.4 Greenlandian Coastal Tundra (plate 4) 1,111 .5 Arctic Alpine Tundra (plate 5) 1,111 .6 Rocky Mountain and Great Basin Alpine Tundra (plate 6)• 1,111 .7 Cascade-Sierran Alpine Tundra (plate 7) 1, 111 .8 Adirondack-Appalachian Alpine Tundra (plate 8) 1,111 .9 Transvolcanic Alpine Tundra (plate 9) 1,111 .1a Madrean (Cerro Potos) Alpine Tundra (plate 10) 120. Forest and Woodland Formationb 121 . Boreal and Subalpine Forest and Woodland 121.1 Alaska-Yukon Subarctic Conifer Forest (plate 11) 121 .2 Canadian Taiga (plate 12) 121 .21 White Spruce-Balsam Fir Series* 121 .22 Black Spruce Series* 121.3 Rocky Mountain and Great Basin Subalpine Conifer Forest (plate 13) 121 .31 Engelmann Spruce-Alpine Fir Series* 121.32 Bristlecone Pine-Limber Pine Series* 121.4 Cascade-Sierran Subalpine Conifer Forest (plate 14) • Further consideration may warrant separation of this biotic community into Rocky Mountain and Great Basin biotic communities. b The first "1" (in front of the comma and representing th e Nearctic realm) is understood and dropped from this point onward for tabular convenience only . TH E CLASS IFI CA TION SYST EM 121.41 Limber Pine- Lodgepole Pine Series* 121.42 Whitebark Pine Series* 121.43 Mountain Hemlock Series* 121 .5 Adirondack-Appalachian Subalpine Conifer Forest (plate 15) 121.51 Red Spruce-Balsam Fir Series* 121 .6 Madrean Subalpine Conifer Forest 121 .61 Hartweg Pine Series* 121.7 Transvolcanic Subalpine Conifer Forest (plate 16) 121 .71 Hartweg Pine Series* 121 .72 Religious Fir Series* 122. Cold Temperate Forest and Woodland 122.1 Northeastern Deciduous Forest (plate 17) 122.11 Oak-Hickory Series* 122.12 Oak-Chestnut Series* 122.13 Beech-Maple Series* 122.14 Oak-Pine Series* 122.15 Maple-Basswood Series* 122.16 Hemlock-White Pine-Mixed Hardwood Series* 122.2 Sitka Coastal Conifer Forest (plate 18) 122.21 Sitka Spruce-Douglas Fir Series* 122.3 Oregonian Coastal Conifer Forest (plate 19) 122.31 Coast Redwood Series* 122.32 Douglas Fir Series* 122.33 Western Hemlock Series* 122.4 Oregonian Deciduous and Evergreen Forest (p!ate 20) 122.41 Mixed Mesophytic Series* 122.42 Oregon White Oak Series* 122.43 Big-cone Spruce Series* 122.5 Cascade-Sierran Montane Conifer Forest (plate 21) 122.51 Mixed Conifer Series* 122.52 Red Fir Series* 122.53 Pacific Silver Fir Series* 122.54 White Fir Series* 122.55 Yellow Pine Series* 122.6 Rocky Mountain Montane Conifer Forest (plate 22) 122.61 Douglas Fir-White Fir (Mixed Conifer) Series* 122.611 Pseudotsuga menziesii Association* 122.612 Pseudotsuga menziesii-Abies concolor Association * 122.613 Pseudotsuga menziesii-mixed conifer Association* 122.614 Populus tremuloides subclimax Association* 122.62 Yellow Pine Series* 122.621 Pinus ponderosa Association * 122.622 Pinus ponderosa-mixed conifer Association * 122.623 Pinus ponderosa-Quercus gambelii Association * 122.624 Pinus ponderosa-Quercus arizonica Association* 122.625 Pinus ponderosa-Juniperus deppeana Association * 122.626 Pinus ponderosa-Abies concolor Association* 122.627 Pinus ponderosa-Pinus f/exilis Association * 122.628 Popu/us tremuloides subclimax Association * 37 NO RT H AMERI CAN BI OTI C CO MM UNITI ES 122.63 Gambel Oak Series* 122.631 Quercus gambelii Association * 122.7 Great Basin Conifer Woodland (plate 23) 122. 71 Pinyan-Juniper Series* 122.8 Madrean Montane Conifer Forest (plate 24) 122.81 Douglas Fir-Mixed Conifer Series* 122.82 Yellow Pine Series* 122.9 Transvolcanic Montane Conifer Forest (plate 25) 122.91 Douglas Fir Series* 122.92 Yellow Pine Series* 122.1 a Guatemalan Montane Conifer Forest (plate 26) 122.1a1 White Pine Series* 123. Warm Temperate Forest and Woodland 123.1 Southeastern Deciduous and Evergreen Forest (plate 27) 123.11 Mixed Mesophytic Series* 123.12 Pine Series* 123.2 California Evergreen Forest and Woodland (plate 28) 123.21 Encinal (Oak) Series* 123.22 Oak-Pine Series* 123.23 Walnut Series* 123.3 Madrean Evergreen Forest and Woodland (plate 29) 123.31 Encinal (Oak) Series* 123.32 Oak-Pine Series* 123.4 Relict Conifer Forest (plate 30) 123.41 Closed-cone Pine Series* 123.42 Cypress Series* 123.5 Transvolcanic Evergreen Forest and Woodland (plate 31) 123.51 Mixed Encinal Series* 123.6 Guerreran Evergreen Forest and Woodland (plate 32) 123.61 Encinal Series* 123.7 Guatemalan Cloud Forest (plate 33) 123.71 Encinal- Mixed Hardwood Series* 123.8 Guatemalan Evergreen Forest and Woodland (plate 34) 123.81 Pine-Oak Series* 123.9 Veracruz Cloud Forest (plate 35) 123.91 Oak-Mixed Hardwood Series* 123.1 a San Lucan Evergreen Forest and Woodland (plate 36) 123.1a1 Encinal Series* 130. Scrubland Formation 131. Arctic-Boreal Scrubland 131.1 Alaskan Coastal Scrub (plate 37) 131.11 Birch-Willow Series* 131.2 Canadian Subpolar Scrub (plate 38) 131 .21 Birch-Willow Series* 131 .3 Alaskan Alpine and Subalpine Scrub (plate 39) 131.31 Willow Series* 131.4 Rocky Mountain Alpine and Subalpine Scrub (plate 40) 131.41 Willow Series* 131.42 Spruce Elfinwood Series* 131.43 Bristlecone Pine Elfinwood Series* TH E CLASS IFI CATION SYSTEM 131.5 Cascade-Sierran Alpine and Subalpine Scrub (plate 41) 131 .51 Limber Pine-Lodgepole Pine Elfinwood Series* 131.52 Whitebark Pine Elfinwood Series* 131 .6 Adirondack-Appalachian Alpine and Subalpine Scrub (plate 42) 131 .61 Hobblebush Series* 131 .7 Madrean Alpine and Subalpine Scrub (plate 43) 131 .71 Prostrate Pinyan Scrub* 132. Cold Temperate Scrubland 132.1 Great Basin Montane Scrub (plate 44) 132.11 Oak-Scrub Series* 132.12 Mountain-Mahogany Series* 132.13 Maple-Scrub Series* 132.14 Serviceberry Series* 132.15 Bitterbrush Series* 132.16 Mixed Deciduous Series* 132.2 Cascade-Sierran Montane Scrub 132.21 Manzanita Series* 132.3 Madrean Montane Scrub (plate 45) 132.4 Plains Deciduous Scrub (plate 46) 132.31 Oak-Scrub Series* 132.32 Sumac Series* 133. Warm Temperate Scrubland 133.1 California Chaparral (plate 47) 133.11 Chamise Series* 133.12 Scrub Oak Series* 133.13 Manzanita Series* 133.14 Ceanothus Series* 133.2 California Coastalscrub (plate 48) 133.21 Mixed Sage Series* 133.22 Buckwheat Series* 133.3 Southwestern Interior (Arizona) Chaparral (plate 49) 133.31 Scrub Oak Series* 133.32 Manzanita Series* 133.33 Ceanothus Series* 133.4 Chihuahuan Interior (Coahuila) Chaparral (plate 50) 133.41 Scrub Oak Series* 133.5 Southeastern Maritime Scrub (plate 51) 133.51 Scrub Oak Series* 134. Tropical-Subtropical Scrubland 0 140. Grassland Formation 141. Arctic-Boreal Grassland 141 .1 Alaskan Grassland (plate 52) 141 .11 Cottongrass Series* 141 .2 Rocky Mountain Alpine and Subalpine Grassland (plate 53) 141.21 Mixed Bunchgrass Series* 141 .3 Cascade-Sierran Alpine and Subalpine Grassland (plate 54) 141.31 Mixed Bunchgrass Series* 141.4 Adirondack-Appalachian Subalpine Grassland 141 .41 Oatgrass-Herb Series* c Included in the Neotropical realm in this classification. 39 N ORT H AMER ICAN BIOTI C COMMU N IT IES 141.5 Madrean Subalpine Grassland 141 .51 Mixed Forb Series* 141 .6 Transvolcanic Alpine and Subalpine Grassland (plate 55) 141 .61 Zacat6n Series* 142. Cold Temperate Grassland 142.1 Plains Grassland (plate 56) 142.11 Bluestem 'Tall-Grass" Series* 142.12 Grama "Short-Grass" Series* 142.13 Mixed "Short-Grass" Series* 142.131 Shrub-Grass Disclimax Association * 142.2 Great Basin Shrub-Grassland (plate 57) 142.21 Wheatgrass Series* 142.22 Mixed Bunchgrass-Shrub Series* 142.23 Ricegrass Series* 142.24 Sacaton Series* 142.25 Cheatgrass Disclimax Series* 142.3 Oregonian (Pacific Coastal) Grassland (p late 58) 142.31 Mixed Bunchgrass Series* 142.4 Rocky Mountain Montane Grassland (plate 59) 142.41 Mixed Meadow Series* 142.5 Cascade-Sierran Montane Grassland (plate 60) 142.51 Mixed Meadow Series* 143. Warm Temperate Grassland 143.1 Chihuahuan (Semidesert) Grassland (plate 61) 143.11 Grama Grass-Scrub Series* 143.12 Tobosa Grass-Scrub Series* 143.13 Curley-Mesquite Grass-Scrub Series* 143.14 Mixed Grass-Scrub Series* 143.15 Shrub-Scrub Disclimax Series* 143.2 California Valley Grassland (plate 62) 143.21 Annual Disclimax Series* 143.3 Gulf Coastal Grassland (plate 63) 143.31 Beardgrass Series* 150. Desertland Formation 151. Arctic-Boreal Desertland 151.1 Polar Desertscrubd 151 .11 Moss-Lichen Series* 152. Cold Temperate Desertland 152.1 Great Basin Desertscrub (plate 64) 152.11 Sagebrush Series* 152.12 Shadscale Series* 152.13 Blackbrush Series* 152.14 Rabbitbrush Series* 152.15 Winterfat Series* 152.16 Mixed Scrub Series* 152.17 Saltbush Series* 153. Warm Temperate Desertland 153.1 Mohave Desertscrub (plate 65) d Included and mapped as "Polar Tundra" in this classification. THE CLASSIFICATIO N SYST EM 153.11 Creosotebush-White Bursage Series* 153.12 Blackbrush Series* 153.13 Mesquite Series* 153.14 Bladdersage Series* 153.15 Joshuatree Series* 153.16 Saltbush Series* 153.2 Chihuahuan Desertscrub (plate 66) 153.21 Creosotebush-Tarbush Series* 153.22 Whitethorn Series* 153.23 Sandpaperbush Series* 153.24 Mesquite Series* 153.25 Mixed Scrub-Succulent Series* 153.26 Saltbush Series* 154. Tropical-Subtropical Desertland 3,000. NEOTROPICAL REALM 3, 100. Natural Upland Vegetation 3,110. Tundra and Paramo Formation 3,111 . Alpine Paramo 3, 111 .1 Central American Paramo+ (plate 67) 120. Forest and Woodland Formation• 124. Tropical-Subtropical Forest and Woodland 124.1 Central American Cloud Forest+ (plate 68) 124.2 Central American Evergreen Rain Forest+ (plate 69) 124.3 Central American Semi-Evergreen Forest+ (plate 70) 124.4 Central American Dry Forest+ (plate 71) 124.5 Campechian Montane Evergreen Forest+ (plate 72) 124.6 Campechian Semi-Evergreen Forest+ (plate 73) 124.7 Yucatan Semi-Deciduous Forest+ (plate 74) 124.8 Yucatan Dry Deciduous Forest+ (plate 75) 124.9 Guerreran Dry Deciduous Forest+ (plate 76) 124.1a Veracruz Evergreen Rain Forest+ (plate 77) 124.1 b Veracruz Semi-Evergreen Forest+ (plate 78) 124.1 c Nayarit-Guerreran Semi-Evergreen Forest+ (plate 79) 124.1d Sinaloan Dry Deciduous (Monsoon) Forest+ (plate 80) 124.1 e Tamaulipan Semi-Deciduous Forest+ (plate 81) 124.1 f San Lucan Dry Deciduous Forest+ (plate 82) 124.1 g Caribbean Cloud and Montane Evergreen Forest (plate 83) 124.1g1 Ocotea-Roble de Sierra Series* 124.1h Caribbean Lowland Evergreen and Semi-Evergreen Forest (plate 84) 124.1 h1 Pine Series* 124.1h2 Palm Series* 124.1 i Caribbean Dry Forest (plate 85) 124.1 i1 Mixed Short Tree Series* 124.1 j Floridian Evergreen (Hammock) Forest (plate 86) 124.1j1 Mixed Hardwood Series* 130. Scrubland Formation 134. Tropical-Subtropical Scrubland • The first "3" (in front of the comma and representing the Neotropical realm) is understood and dropped from this point onward for tabular convenience. 42 NO RTH AME RI CAN BI OTI C CO MM UN ITI ES 134.1 Guerreran Thornscrub+ (plate 87) 134.2 Sinaloan Thornscrub (plate 88) 134.21 Mixed Deciduous Series* 134.3 Tamaulipan Thornscrub (plate 89) 134.31 Mixed Deciduous Series* 134.32 Mesquite Disclimax Series* 134.4 San Lucan Thornscrub+ (plate 90) 134.5 Caribbean Thornscrub+ (plate 91) 134.6 Central American Thornscrub+ (plate 92) 140. Grassland Formation 144. Tropical-Subtropical Grassland 144.1 Central American Savanna Grassland+ (plate 93) 144.2 Guerreran Savanna Grassland+ (plate 94) 144.3 Campechian and Veracruz Savanna Grassland+ (plate 95) 144.4 Caribbean Savanna Grassland+ (plate 96) 144.5 Sonoran Savanna Grassland+ (plate 97) 144.6 Tamaulipan Savanna Grassland+ (plate 98) 150. Desertland Formation 154. Tropical-Subtropical Desertland 154.1 Sonoran Desertscrub (plates 99 and 100) 154.11 Creosotebush-White Bursage (Lower Colorado Valley) Series* 154.12 Paloverde-Mixed Cacti (Arizona Upland) Series* 154.13 Brittlebush-lronwood (Plains of Sonora) Series* 154.14 Copal-Torote (Central Gulf Coast) Series* 154.15 Agave-Bursage (Vizcaino) Series* 154.16 Paloblanco-Agria (Magdalena Plain) Series* 154.17 Saltbush Series* THE CLASS IFICATIO N SYSTEM Table 5. Nomenclature of wetland biotic communities for Nearctic and Neotropical North America Some series (fifth level) examples are provided here for demonstration purposes and indicated by an asterisk (*). A plus sign (+) indicates biotic communities for which our incomplete knowledge precludes presentation of representative series and association examples . 1,000. NEARCTIC REALM 1,200. Natural Wetland Vegetation 1,210. Wet Tundra Formation 1,211. Arctic Wet Tundra (plate 101) 1,211.1 Polar (High Arctic) Wet Tundra 1,211.11 Sedge-Moss Series* 1 ,211.12 Rush Series* 1,211 .2 Greenlandian Wet Tundra 1,211 .21 Sedge-Moss Series* 1,211.3 Alaskan (Coastal) Wet Tundra 1,211 .31 Sedge-Moss Series* 1,211.4 Canadian (Low Arctic) Wet Tundra 1,211.41 Sedge-Grass-Moss Series* 1,211.42 Rush Series* 220. Forest Formation• 221 . Boreal Swamp and Riparian Forest (plate 102) 221.1 Canadian Swamp Forest 221.11 Black Spruce-Tamarack Series* 221.12 Willow-Alder Series* 222. Cold Temperate Swamp and Riparian Forest (plate 103) 222.1 Northeastern Bog, Swamp, and Riparian Forests 222.11 White Cedar Series* 222.12 Cottonwood-Willow Series* 222.13 Ash-Maple Series* 222.2 Plains and Great Basin Riparian Deciduous Forest 222.21 Cottonwood-Willow Series* 222.3 Oregonian (Pacific Coastal) Riparian Deciduous Forest 222.31 Cottonwood-Willow Series* 222.4 Cascade-Sierran Riparian Deciduous Forest 222.41 Cottonwood-Willow Series* 222.42 Mixed Broadleaf Series* 222.5 Rocky Mountain Riparian Deciduous Forest 222.51 Cottonwood-Willow Series* 222.52 Mixed Broadleaf Series* 223. Warm Temperate Swamp and Riparian Forests (plate 104) 223.1 Southeastern Swamp and Riparian Forest 223.11 Tupelo-Cypress Series* 223.12 Southern White Cedar Series* 223.13 Mixed Hardwood Series* 223.14 Cottonwood-Willow Series* 223.2 Southwestern Riparian Deciduous Forest and Woodland 223.21 Cottonwood-Willow Series* 223.22 Mixed Broadleaf Series* 223.3 California Riparian Deciduous Forest and Woodland 223.31 Cottonwood-Willow Series* 223.32 Mixed Broadleaf Series* The first "1" in front of the comma and representing the Nearctic realm is understood and dropped from this point onward for tabular convenience only. a 43 N O RT H AM ERI CAN BI O TI C CO M MU NI TIES 44 224 . Tropical-Subtropical Swamp, Riparian , and Oasis Forestb 230. Swamp Scrub Formation . \ 231 . Arct1c-Boreal Swamp Scrub (plate 105) 231 .1 Polar (High Arctic) Swamp Scrub 231.11 Willow Series* 231.2 Greenlandian Swamp Scrub 231 .21 Willow Series* 231 .3 Alaskan Swamp Scrub 231 .31 Willow Series* 231.4 Canadian Swamp Scrub 231.41 Willow Series* 231.42 Leatherleaf Series* 231 .5 Adirondack-Appalachian Alpine and Subalpine Swamp and Riparian Scrub 231 .51 Willow Series* 231.6 Cascade-Sierran Alpine and Subalpine Swamp and Riparian Scrub 231 .61 Willow Series* 231 .7 Rocky Mountain Alpine and Subalpine Swamp and Riparian Scrub 231 .71 Willow Series* 232 . Cold Temperate Swamp and Riparian Scrub (plate 106) 232 .1 Northeastern Deciduous Swamp Scrub 232.11 Willow Series* 232.12 Sweet Gale Series* 232.13 Buttonbush Series* 232 .14 Cranberry Series* 232 .15 Mixed Narrowleaf Series* 232 .2 Plains and Great Basin Riparian Scrub 232 .21 Willow Series* 232 .22 Saltcedar Disclimax Series* 232.3 Oregonian Swamp and Riparian Scrub 232.31 Willow Series* 232.32 Mixed Narrowleaf Series* 232.4 Cascade-Sierran Swamp and Riparian Scrub 232.41 Willow Series* 232 .5 Rocky Mountain Swamp and Riparian Scrub 232 .51 Willow-Dogwood Series* 233. Warm Temperate Swamp and Riparian Swamp Scrub (plate 107) 233.1 Southeastern Mixed Deciduous and Evergreen Swamp Scrub 233 .11 Mixed Broadleaf Series* 233 .2 Southwestern Interior Swamp and Riparian Scrub 233.21 Seepwillow Series* 233.22 Saltcedar Disclimax Series* 233.3 California Swamp and Riparian Scrub 233.31 Mixed Narrowleaf Series* 233.4 Mohave Swamp and Riparian Scrub 233.41 Saltcedar Disclimax Series* 233.5 Chihuahuan Swamp and Riparian Scrub 233.51 Saltcedar Disclimax Series* 240 . Marshland Formation 241 . Arctic-Boreal Marshland (plate 108) 241 .1 Polar (High Arctic) Marshland 241 .11 Sedge Series* 241 .12 Rush Series* 241 .2 Greenlandian Marshland b See Neotropical realm. THE CLASSIFICATIO N SYSTEM 241.21 Sedge Series* 241 .22 Rush Series* 241.3 Alaskan Interior Marshland 241.31 Sedge Series* 241 .4 Alaskan Maritime (Coastal) Marshland 241.41 Sedge Series* 241 .5 Canadian Interior Marshland 241.51 Sedge Series* 241.6 Canadian Maritime Marshland 241.61 Sedge Series* 241 .7 Adirondack-Appalachian Alpine and Subalpine Marshland 241. 71 Sedge Series* 241.8 Cascade-Sierran Alpine and Subalpine Marshland 241 .81 Sedge Series* 241.9 Rocky Mountain Alpine and Subalpine Marshland 241.91 Sedge Series* 241 .92 Rush Series* 241.93 Manna Grass Series* 242. Cold Temperate Marshland (plate 109) 242.1 Northeastern Interior Marshland 242.11 Sedge Series* 242.12 Rush Series* 242.13 Bur-Reed Series* 242.14 Cattail Series* 242.15 Bulrush Series* 242.16 Arrow-Arum Series* 242.17 Reed Canarygrass Series* 242.18 Waterlily Series* 242.2 Northeastern Maritime Marshland 242.21 Saltgrass Series* 242.3 Plains Interior Marshland 242.31 Sedge Series* 242.32 Rush Series* 242.4 Great Basin Interior Marshland 242.41 Sedge Series* 242.5 Oregonian Interior Marshland 242.51 Sedge Series* 242.6 Oregonian (Pacific Coastal) Maritime Marshland 242.61 Saltgrass Series* 242.62 Glasswort Series* 242.7 Cascade-Sierran Montane Marshland 242.71 Sedge Series* 242.8 Rocky Mountain Montane Marshland 242.81 Sedge Series* 242.82 Rush Series* 243. Warm Temperate Marshland (plate 110) 243.1 Southeastern Interior Marshland 243.11 Cattail Series* 243.2 Southeastern Maritime Marshland 243.21 Saltmarshgrass Series* 243.3 Gulf Coastal Maritime Marshland 243.31 Saltgrass Series* 243.4 Southwestern Interior Marshland 243.41 Sedge Series* 243.5 Mohave Interior Marshland 45 NORTH AM ERIC AN BIOTI C COMMUN ITI ES 243.51 Sedge Series* 243.6 Chihuahuan Interior Marshland 243.61 Saltgrass Series* 243.7 Madrean Marshland 243.71 Sedge Series* 243.8 Everglades Interior Marshland 243.81 Sawgrass Series* 243.9 California Interior Marshland 243.91 Sedge Series* 243.1 a California Maritime Marshland 243.1a1 Cordgrass Series* 243.1 a2 Glasswort Series* 250. Strand Formation 251. Arctic-Boreal Strand (plate 111) 251 .1 Polar Maritime Strand+ 251 .2 Greenlandian Interior Strand+ 251 .3 Greenlandian Maritime Strand+ 251.4 Alaskan Interior Strand+ 251.5 Alaskan Maritime Strand+ 251.6 Canadian Interior (Stream and Lake) Strand+ 251 .7 Canadian Maritime Strand+ 251 .8 Adirondack-Appalachian Alpine and Subalpine Strand+ 251.9 Cascade-Sierran Alpine and Subalpine Strand+ 251 .1a Rocky Mountain Alpine and Subalpine Strand+ 252. Cold Temperate Strand (plate 112) 252.1 Northeastern Interior (Stream and Lake) Strand+ 252.2 Northeastern Maritime Strand 252.21 Sandreed Series* 252.3 Plains Stream and Lake Strand 252.31 Mixed Annual Series* 252.4 Great Basin Interior Strand 252.41 Mixed Annual Series* 252.5 Oregonian Interior Strand+ 252.6 Oregonian Maritime Strand+ 252.7 Cascade-Sierran Stream and Lake Strand+ 252.8 Rocky Mountain Stream and Lake Strand+ 253. Warm Temperate Strand (plate 113) 253.1 Southeastern Interior Strand+ 253.2 Southeastern Maritime Strand+ 253.3 Southwestern Interior Strand+ 253.4 California Interior Strand 253.41 Mixed Annual Series* 253.5 California Maritime Strand 253.51 Mixed Scrub Series* 253.52 Sea-grass Series* 253.53 Green Algae Series* 253.54 Red Algae Series* 253.55 Brown Algae Series* 253.6 Mohave Interior Strand+ 253.7 Chihuahuan Interior Strand+ 253.8 Madrean Stream and Lake Strand+ THE CLASSIFICATIO N SYSTEM ｾ＠ 3,000. NEOTROPICAL REALM 3,200. Neotropical Natural Wetland Vegetationc 3,220. Forest Formation 3,224. Tropical-Subtropical Swamp, Riparian, and Oasis Forest and Woodland (plates 114 and 115) 224.1 Floridian Interior Swamp and Riparian Forestd 224.11 Mixed Evergreen Series* 224.12 Palm Communities* 224.2 Floridian Maritime Swamp Forest 224.21 Mangrove Series* 224.3 Tamaulipan Interior Swamp and Riparian Forest 224.31 Mixed Evergreen Series* 224.32 Palm Series* 224.4 Sonoran Riparian and Oasis Forest 224.41 Palm Series* 224.42 Mesquite Bosque Series* 224.43 Cottonwood-Willow Series* 234. Tropical-Subtropical Swamp and Riparian Scrub (plate 116) 234.1 Floridian Interior Swamp Scrub 234.11 Mixed Evergreen Series* 234.2 Floridian Maritime Swamp Scrub 234.21 Mangrove Series* 234.3 Gulf Coastal Interior Swamp and Riparian Scrub 234.31 Mixed Evergreen Series* 234.4 Gulf Coastal Maritime Swampscrub 234.41 Mangrove Series* 234.5 Sonoran Riparian Scrub 234.51 Mixed Scrub Series* 234.52 Seepwillow Series 234.53 Saltcedar Disclimax Series* 244. Tropical-Subtropical Marshland (plate 117) 244.1 Floridian Interior Marshland 244.11 Cattail Series* 244.12 Bulrush Series* 244.13 Giant Reed Series* 244.14 Sawgrass Series* 244.2 Floridian Maritime Marshland 244.21 Saltgrass Series* 244.3 Gulf Coastal Interior Marshland 244.31 Cattail Series* 244.32 Bulrush Series* 244.33 Giant Reed Series* 244.4 Gulf Coastal Maritime Marshland 244.41 Saltgrass Series* 244.5 Sonoran Interior Marshland 244.51 Cattail Series* 244.52 Bulrush Series* 244.53 Giant Reed Series* 244.54 Threesquare Series* 254. Tropical-Subtropical Strand (plate 118) 254.1 Floridian Interior Strand+ 254.2 Floridian Maritime Strand+ Neotropical examples are given only for those biotic communities occurring in the United States. The first "3" in front of the comma and representing the Neotropical realm is understood and dropped from this point onward for tabular convenience only. 47 NORTH AME RI CA 254.3 Gulf Coastal Interior Strand+ 254.4 Gulf Coastal Maritime Strand+ 254.5 Sonoran Interior Strand 254.51 Mixed Shrub Series* BIO TI C COMMUN ITIES 3 The Biotic Communities of North America Map The accompanying l:ro,000,000 color map (Reichenbacher, Franson, and Brown 1998) depicts the continent's major biotic communities (fourth level of the classification system) using Gaussen's (19 53) ecological color-scheme that illustrates gradients in available plant moisture, heat, and cold. The base map was reproduced from an acetate overlay of a 1:8,000,000 Ki.immerly and Frey stereographic chart, and the biotic communities delineated in eighty-three vinyl colors using as source data the maps, terminology, and descriptions found in the Literature Cited and Literature Consulted as well as our own field work. The biotic communities shown depict regional formations within recognized biotic and floristic provinces as modified from Dice (1943), Goldman and Moore (1945), Shreve (19 51), Rzedowski (19 78), Barbour and Billings (1988), and other biogeographers. The boundaries and terminology of the various biotic communities, while derived from numerous works, are modeled after papers developed by the IUCN and UNESCO and proposed for use in the International Biosphere Reserve program (Udvardy l984a, l984b). Neither the biotic community designations nor their delineations are final. Eventually, it is hoped that the use of high-altitude imagery and other recently developed techniques (see, e.g., Loveland et al. 1991 ) will result in an improved depiction of the boundaries of these biotic resources. Because of the limitations of scale, upland biotic communities such as Relict Conifer Forests and Central American Thornscrub, occupying individual areas less than ca. roo square kilometers in size, are omitted from the map. Their enormous diversity, dynamic na ture, and generally limited area also precluded illustration of all but the largest wetlands. The biogeographic affiliation of these or any other wetlands can be readily determined by referring to the upland biotic community within which they occur. It is expected that further research and peer review will result in improvements in the nomenclature and delineation of the biotic communities depicted, particularly those in Latin America. Some potential users and reviewers have objected to the large uniform areas of Northeastern Deciduous Forest, Canadian Taiga, and Plains Grassland when compared to the smaller, more numerous biotic communities in Mexico and the American Southwest. This apparent discrepancy is real, however, at the biotic community level. For the reasons already stated, biotic diversity increases as one 49 NORTH AMERICAN BIOTIC COMMUNITIES travels westward and southward across the North American continent- a phenomenon long recognized by biologists (e.g., Simpson 1964, Kiester 1971, and Wilson 1974). Mexico, despite having only l l percent of the land area of Canada and the United States, has more species of mammals, birds, and reptiles and amphibians than the two northern countries combined. One Mexican state, Chiapas, has 8,250 known species of plants as compared to the much larger (115,719 versus 74,000 square kilometers) and botanically rich American state of Ohio, which has 2,700 species (Ramamoorthy et al. 1993). It is only reasonable then to show the southern parts of North America as possessing greater variation at the biotic community level than the northern and eastern portions of the continent (Klopfer and MacArthur 1960; Fleming 1973; Wilson 1974). Nonetheless, further research may show that one or more of the biotic communities depicted are not sufficiently distinct to warrant fourth-level separation. Future investigators, for example, may conclude that the Neotropical Realm's Guerreran Deciduous Forest is not sufficiently different from Sinaloan Deciduous Forest to justify separate biotic community status. Conversely, additional study may support the division of the Caribbean Biotic Province into Greater Antillean and Lesser Antillean provinces as proposed by Udvardy (1975b). Also, should additional biotic detail be desired within a major biotic community, future editions of the map can provide series or fifth -level community designations as was done for the Northeastern Deciduous Forest by Braun (1950) and for Sonoran Desertscrub by Shreve (1951) and Brown and Lowe (1980, 1994). The map has been digitized by the Environmental Protection Agency's National Exposure Research Laboratory, Characterization Research Division, Las Vegas, Nevada. Digitization will facilitate modifying the map's biotic communities based on peer review and allow for the possible overlay of land-use data. Digitization will also facilitate the division of larger biotic communities such as the Northeastern Deciduous Forest and Plains Grassland into large general series, should such further subdivision be desired. One immediate use of the map is for estimating the areas of North America's biotic communities (table 6). Such information will enable biologists to stratify their samples in a more meaningful way, thereby improving the precision and efficiency of wildlife surveys. A continental sample frame is especially useful for conducting breeding dove and other migratory bird surveys similar to those presently being coordinated by the U.S. Fish and Wildlife Service. Even more important, knowing the areal extent of biotic communities permits a better assessment and appreciation of those areas still remaining in a natural state. In summation, the purpose of the map is to illustrate the applicability of the classification system for inventorying the continent's biotic resources and to provide a sample frame for those interested in stratifying natural history surveys. With the recent availability of highly detailed aerial imagery, one could feasibly now also overlay land-use, thus measuring the extent of those biotic communities re- THE BIOTIC COMMUNITIES OF NORTH AMERICA MAP maining in a natural state. National park boundaries and other enhancements would also enable resource managers to identify those biotic communities having protected status and determine which are in need of additional protection. A biotic communities map also facilitates the evaluation of candidate areas for biosphere reserve and wilderness status. Enhanced with land use information, such a map can also assist in the interpretation of environmental change. Table 6. Areas of North American biotic communities Areas (in 1,000 square kilometers) were derived from the digital data of the Map of the Biotic Communities of North America. 1,000. NEARCTIC REALM 1, 100. Natural Upland Vegetation 21,720 21,416 1, 110. Tundra Formation 111. Arctic and Alpine Tundra 111.1 Polar (High Arctic) Tundra 610 111.2 Alaskan Tundra 168 111 .3 Canadian (Low Arctic) Tundra 2,262 111.4 Greenlandian Coastal Tundra 364 111 .5 Arctic Alpine Tundra 486 111.6 Rocky Mountain- Great Basin Alpine Tundra 111.7 Cascade-Sierran Alpine Tundra 51 4 111 .8 Adirondack-Appalachian Alpine Tundra <1 111.9 Transvolcanic Alpine Tundra <1 120. Forest and Woodland Formation 121 . Boreal and Subalpine Forest and Woodland 121.1 Alaska-Yukon Subarctic Conifer Forest 121.2 Canadian Taiga 121 .3 Rocky Mountain and Great Basin Subalpine Conifer Forest 919 4,631 396 121.4 Cascade-Sierran Subalpine Conifer Forest 55 121.5 Adirondack-Appalachian Subalpine Conifer Forest 17 122. Cold Temperate Forest and Woodland 122.1 Northeastern Deciduous Forest 2,712 122.2 Sitka Coastal Conifer Forest 209 122.3 Oregonian Coastal Conifer Forest 124 122.4 Oregonian Deciduous and Evergreen Forest 36 122.5 Cascade-Sierran Montane Conifer Forest 149 122.6 Rocky Mountain Montane Conifer Forest 554 122.7 Great Basin Conifer Woodland 299 122.8 Madrean Montane Conifer Forest 37 122.9 Transvolcanic Montane Conifer Forest 6 122.1 a Guatemalan Montane Conifer Forest 5 52 NO RT H AMERI CAN BI O TI C CO M MUN ITIES 123. Warm Temperate Forest and Woodland 123.1 Southeastern Deciduous and Evergreen Forest 630 123.2 California Evergreen Forest and Woodland 62 123.3 Madrean Evergreen Forest and Woodland 218 123.5 Transvolcanic Evergreen Forest and Woodland 57 123.6 Guerreran Evergreen Forest and Woodland 42 123. 7 Guatemalan Cloud Forest 15 123.8 Guatemalan Evergreen Forest and Woodland 67 123.9 Veracruz Cloud Forest 123.1 a San Lucan Evergreen Forest and Woodland 6 >1 130. Scrubland Formation 132. Cold Temperate Scrubland 132.1 Great Basin Montane Scrub 29 133. Warm Temperate Scrubland 133.1 California Chaparral 34 133.2 California Coastalscrub 27 133.3 Southwestern Interior Chaparral 11 133.4 Chihuahuan Interior Chaparral 30 140. Grassland Formation 142. Cold Temperate Grassland 142.1 Plains Grassland 142.2 Great Basin Shrub-Grassland 2,341 524 143. Warm Temperate Grassland 143.1 Chihuahuan (Semidesert) Grassland 143.2 California Valley Grassland 71 143.3 Gulf Coastal Grassland 52 150. Desertland Formation 508 836 152. Cold Temperate Desertland 152.1 Great Basin Desertscrub 332 153. Warm Temperate Desertland 153.1 Mohave Desertscrub 124 153.2 Chihuahuan Desertscrub 380 161. Permanent Ice and Snow 200. Nearctic Natural Wetland Vegetation 3,000. Neotropical Realm 3, 100. Natural Upland Vegetation 1,760 304 1,847 1,784 3, 110. Tundra and Paramo Formation 111. Alpine Paramo 111 .1 Central American Paramo <1 120. Forest and Woodland Formation 124. Tropical-Subtropical Forest and Woodland 124.1 Central American Cloud Forest 124.2 Central American Evergreen Rain Forest 15 161 T H E BIOTIC COMMUNITI ES OF NORTH AME RI CA MA P 53 124.3 Central American Semi-Evergreen Forest 48 124.4 Central American Dry Forest 33 96 124.5 Campechian Montane Evergreen Forest 124.6 Campechian Semi-Evergreen Forest 124.7 Yucatan Semi-Deciduous Forest 16 124.8 Yucatan Dry Deciduous Forest 24 124.9 Guerreran Dry Deciduous Forest 107 139 124.1a Veracruz Evergreen Rain Forest 35 124.1 b Veracruz Semi-Evergreen Forest 35 124.1c Nayarit-Guerreran Semi -Evergreen Forest 34 124.1 d Sinaloan Dry Deciduous Forest 67 124.1e Tamaulipan Semi-Deciduous Forest 38 124.1f San Lucan Dry Deciduous Forest 124.1 g Caribbean Cloud and Montane Evergreen Forest 124.1h Caribbean Lowland Evergreen and Semi-Evergreen Forest 124.1i Caribbean Dry Forest 124.1 j Floridian Evergreen (Hammock) Forest 5 19 55 109 2 130. Scrubland Formation 134. Tropical-Subtropical Scrubland 134.1 Guerreran Thornscrub 35 134.2 Sinaloan Thornscrub 62 134.3 Tamaulipan Thornscrub 188 134.4 San Lucan Thornscrub 7 134.5 Caribbean Thornscrub 12 140. Grassland Formation 144. Tropical-Subtropical Grassland 144.1 Central American Savanna Grassland 69 144.2 Guerreran Savanna Grassland 15 144.3 Campechian-Veracruz Savanna Grassland 13 144.4 Caribbean Savanna Grassland 37 150. Desertland Formation 154. Tropical-Subtropical Desertland 154.1 Sonoran Desertscrub 3,200. Neotropical Natural Wetland Vegetation 306 62 55 Plater. Polar (High Arctic) Tundra (rrr.r) on Ellesmere Island, Northwest Territories, Canada. Note the low stature of the "heath" and the large areas of barren, stony ground. Photo courtesy of R. E. Hamburg, Travel Arctic, Government of the Northwest Territories. Plate 2. Alaskan Tundra (rrr.2) of low-growing grasses and sedges on Denali (Mount McKinley) National Park and Preserve. The caribou are the Alaskan subspecies, Rangifer tarandus granti. National Park Service photo. Plate 3. Canadian (Low Arctic) Tundra (rrr.3) west of Hudson Bay, just so uth of the town of Ch urchill in Manitoba, Canada. It is November and the only plants protruding through the snow cover are a few shrubby willows (Salix sp.) and a very open stand of stunted black spruce (Picea mariana). Immediately to the south lies the boreal forest or Canadian Taiga. Photo by D. E. Brown. Plate 4. Greenlandian Coastal Tundra ( rr r.4) and musk-oxen (Ovibos moschatus) near Sondre Stronfjord in southwest Greenland. Note the stature of the heath vegetation in comparison to plate r. Photo taken in July 1995 by Melvin Marcus. 57 Plate 5. Arctic Alpine Tundra (rrr.5) and Dall sheep (Ovis dalli) in the Cathedral Mountains, Denali National Park and Preserve, Alaska. Note the large areas of bare ground in this open "Dryas-Lichen community" at ca. 1350 m (4430 ft) altitude. Photo by D. E. Brown . Plate 6. Rocky Mountain Alpine Tundra ( r r r.6) in the Rio Grande National Forest, Colorado, ca. 3 ,900 m (12,800 ft) altitude. It is midsummer and many of the alpine plants, which include Kobresia myosuroides, Polygonum bistortoides, Trifolium nanum, and Geum rossi, are in bloom. U. S. Forest Service photo taken by H. E. Schwan on August 8, r 94 5. 58 Plate 7. Cascade-Sierran Alpine Tundra (11r.7) at ca. 2900 rn (9 500 ft) altitude in the Sierra Nevada, Washoe County, Nevada. Steep terrain and a windswept ridge inimical to tree growth allow this rocky-fell field of bare rock and prostrate shrubs to extend below the usual occurrence of alpine tundra in the Sierra Nevada. Photo taken by Richard E. Brown in September 199 5. Plate 8. Adirondack-Appalachian Alpine Tundra (11r.8). A view of the summit area of Mount Washington in New Hampshire's White Mountains, ca. 1830 m (6000 ft) altitude. Several species of lichens and mosses are present in addition to a single species of sedge (Carex bigelowii) in this "rock-fell" habitat. Photo by D. E. Brown. 59 Plate 9. Transvolcanic Alpine Tundra (rrr.9 ). A view of the still active Volcan de Fumeral from the uppermost slopes of the Sierra de Colima in Jalisco, Mexico. The altitude is ca. 4250 m (13900 ft). In this open and depauperate alpine community at latitude 19 degrees North, the number of plant species present can literally be counted on one's fingers. Photo by D. E. Brown. Platero. Madrean Alpine Tundra (11r.1a) atop Cerro Potosi, Nuevo Leon, Mexico, at ca. 3700 m (12140 ft) populated by short-statured forbs such as Potentilla leonina, Arenaria sp., Bidens muelleri, Lupinus cacuminis, Senecio scalaris, and Castilleia bella (Beaman and Andresen 1966). The almost total lack of grasses in this "alpine meadow" may be at least partially due to grazing pressures (note dairy cattle in background). Photo by D. E. Brown. 60 Plate rr. Alaska-Yukon Subarctic Conifer Forest (12r.1) consisting mostly of white spruce (Picea glauca) in Denali National Park and Preserve, Alaska. Photo by D. E. Brown. Plate 12. Canadian Taiga (12r.2). Boreal communities such as this virgin stand of black spruce (Picea mariana) in Minnesota's Big Falls Experimental Forest extend southward into the northern tier of U.S. states on poorly drained acidic soils. The understory is commonly a feathermoss, in this case probably Pleurozium schreberi. U. S. Forest Service photo by L. P. Neff. 61 Plate 13. Rocky Mountain Su balpine Conifer Forest (12r.3) of Engelmann spruce (Picea engelmanni) and alpine fir (Abies lasiocarpa) at an altitude of ca. 2600 m (8500 ft) in the Arapaho National Forest in Colorado. U. S. Forest Service photo taken by E. S. Shipp in 1927. Plate 14. Cascade-Sierran Subalpine Conifer Forest (12r.4) in Olympic National Park, Washington. The trees at this altitude, which is ca. l 500 m (5000 ft), are mostly mountain hemlock (Tsuga mertensiana) and Pacific silver fir (Abies amabilis). National Park Service photo taken in 1934· Plate 15. Adirondack-Appalachian Subalpin e Conifer Forest (12r.5). This virgin red spruce (Picea rubens) forest on Barton's Knob in the so uthern Appalachian Mountains near Durbin, West Virginia, is one of the south ern most fasciations of this biotic commu nity. U. S. Forest Service photo taken in August 1939 by Leon S. Minckler. Plate 16. Transvolcanic Subalpine Conifer Forest (12r.7) of Hartweg pines (Pinus hartwegii), Montezuma pines (Pinus montezumae), and alder (Alnus firmifolia) extending from ca. 30 50 m (10000 ft) altitude to timberline in the Sierra Nevada de Colima, Jalisco, Mexico. Photo by D. E. Brown. Plate 17. Northeastern Deciduous Forest (122.1). This Beech (Fagus grandifolia)-Maple (Acer saccharum) series on the Bartlett Experimental Forest in New Hampshire is representative of but one of severa l major fasciations of this important and extensive biotic community. U. S. Forest Service photo taken in August 1938 by Victor S. Jensen. Plate 18. Sitka Coastal Conifer Forest (122.2) dominated by Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) in the Tongass National Forest, Alaska. U.S. Forest Service photo taken by H. L. Shantz in June l 9 3 8. Plate 19. Oregonian Coastal Conifer Forest (122.3) comprised of an oldgrowth stand of coast redwoods (Sequoia sempervirens) in Del Norte County, Ca liforni a. The man standing in the lower left of the photo indicates the size of these redwoods. Photo by Douglass P. Roy. Plate 20. Oregonian Deciduous and Evergreen Forest (122-4) at Falling Springs in the San Gabriel Mountains-a southern fasciation of a mixed mesophytic series that extends from Oregon to southern California. Important trees at this 1220 m (4000 ft) altitude location in the Los Angeles Nationa l Forest are big-cone Douglas fir (Pseudotsuga macrocapa), incense cedar (Libocedrus decurrens), and both evergreen oaks (e.g., Quercus chrysolepis) and a deciduous oak (Quercus kelloggi). Photo by D. E. Brown. Plate 2r. Cascade-Sierran Montane Conifer Forest (122.5) represented here by a virgin stand of red fir (Abies magnifica) in the Tahoe National Forest in California's Sierra Nevada. U.S. Forest Service photo taken by W. I. Hutchinson in 1935· 66 Plate 22. Rocky Mountain Montane Conifer Forest (122.6) consisting of an almost pure stand of old-growth ponderosa pines (Pinus ponderosa) with a bunch-grass understory in the White Mountains of Arizona. The altitude is ca. 2500 m (8200 ft). U.S. Forest Service photo taken in August 19 57 by Daniel 0. Todd. Plate 23. Great Basin Conifer Woodland (122.7) of mostly Rocky Mountain juniper (]unip erus scopulorum) and Rocky Mountain pinyon (Pinus edulis) at an altitude of ca. 1800 m (5900 ft) southwest of Flagstaff, Arizona. U. S. Forest Service photo taken in 1920. Plate 24. Madrean Montane Conifer Forest (122.8) at an altitude of ca. 2100 m (6900 ft) along the Sonora-Chihu ahua border. The trees are almost entirely ponderosa pine (Pinus ponderosa var. arizonica). Photo taken by Dirk V. Lan ning about 1979 while he was studying thick-billed parrots (Rhynchopsitta pachyrhyncha) in northern Mexico. Plate 25. Transvolcanic Montane Conifer Forest (122.9) of Douglas fir (Pseudotsuga menziesi) at an altitude of ca. 2600 m (8530 ft) in th e Sierra Angangueo, Michoacan, Mexico. This forest is the winter home of countless migrating monarch butterflies (Danaus plexippus), whose caterpillars feed on the milkweed (Asclepias sp.) understory. Photo by D. E. Brown. 68 Plate 26. Guatemalan Montane Conifer Forest (122.1a) at ca. 2600 m (8500 ft) altitude on the north slopes of Cerro Tecpan off the Pan American Highway northwest of Guatema la City. The trees are almost entirely Holarctic genera and include Pinus ayacahuite, P. pseudostrobus, P. montezumae, Abies guatemalensis, a cypress (Cupressus sp.), and an alder (A/nus sp.). Photo by D. E. Brown. Plate 27. Southeastern Deciduous and Evergreen Forest (123.1) in the Croa tan National Forest in North Carolina. This coastal habitat is domin ated by a nearly pure stand of longleaf pine (Pinus palustrus). U. S. Forest Service photo taken by Daniel 0. Todd in July 1952· Plate 28. California Evergreen Forest and Woodland (123.2) at ca. 340 m (1100 ft) in the San Jose Hills near Pomoma, Los Angeles County, California. This particular woodland of winter deciduous California walnuts Uuglans california) and a few evergreen coast live oaks (Quercus agrifolia) is rapid ly being urbanized and without protection will soon be destroyed if it has not been so already. The dead branches on the walnut trees are thought to be due to a prolonged drought that began in the winter of 1975 and continued until 1977· Photo by D. E. Brown. Plate 29. Madrean Evergreen Forest and Woodland (123.3) ca. 1675 m (5500 ft) altitude in the Sierra de! Nido, Chihuahua, Mexico. The principal trees at this site are Chihuahua pine (Pinus leiophylla), Emory oak or "bellota" (Quercus emoryi), and Mexican piiion (Pinus cembroides). Photo by D. E. Brown. Plate 30. Relict Conifer Forest (123.4). In this case a woodland of Monterey cypress (Cupressus macrocarpa) on the California seacoast in Monterey County. Without the prevailing sea-breeze from the open ocean these trees would soon succumb to wind-borne disease. U. S. Forest Service photo taken in 1903 by A. Gaskill. Plate 3r. Transvolcanic Evergreen Forest and Woodiand (123.5) populated by several species of evergreen oaks (Quercus spp.), at least three pines (Pinus spp.), and a madroiio (Arbutus sp.) at ca. 1830 m (6000 ft) altitude on the eastern slopes of the Sierra Nevada de Colima, Jalisco, Mexico. Photo by D. E. Brown. I 72 Plate 32. Guerreran Evergreen Forest and Woodland (123.6) at ca. 1250 m (4roo ft) in the Sierra Madre de! Sur, Oaxaca, Mexico. The variety of plants in the woodland is large and includes several short-statured oaks and a juniper as well as genera of more so uthern derivation. Photo by D. E. Brown. Plate 33. Guatemalan Cloud Forest (123.7) at 2250 m (7400 ft) altitude near the summit of Sierra de la Tigra, Honduras. Various species of hardwoods, some exceeding 50 m (165 ft) in height, occur in this moisture-laden habitat, which occurs above a forest of Pinus pseudostrobus. Resplendent quetzales (Pharomachrus mocinno) and black penelopinas (Penelopina nigra) are just two of the many interesting birds to be seen and heard in this 7,5 50 hectare National Park. Photo by D. E. Brown. 73 Plate 34. Guatemalan Evergreen Forest and Woodland (123.8). A short-statured forest of "ocote" (Pinus oocarpa) ca. 1 300 m (4300 ft) near Tegucigalpa, Honduras. Where more favorable soils and/or moisture conditions are present, oaks enter the "ocotal" and may become locally dominant. Photo by D. E. Brown. 74 Plate 35. Veracruz Cloud Forest (123.9) of oaks (Quercus skinneri et al.), sweetgum (Liquidamber styraciflua), hickory (Carya sp.), and other temperate trees at ca. II50 m (3775 ft) near Rancho de! Cielo in the Sierra de Guatemala on the east slopes of the Sierra Madre Oriental in southern Tamaulipas, Mexico. Note the tank bromeliads and large load of epiphytes on the trees. At slightly higher elevations, a beech (Fagus mexicana) enters the forest, which shares numerous genera (e.g., Acer, Prunus, Myrica, and Carya) if not species with the Southeastern Deciduous and Evergreen Forest (Martin 1958). This forest is the northernmost home of the singing quail (Dactylartyx thoracicus). Photo by D. E. Brown. 75 Plate 36. San Lucan Evergreen Forest and Woodland (r23.1a) atop the Sierra de la Laguna, Ba ja Ca lifornia Sur, Mexico. The trees present includ e the endem ic "pino pi n6nero" (Pinus lagunae) as well as several end em ic oaks, for example, "encino negro" (Quercus devia). Photo taken on October 14, r9 4 r, by Edward Ross, San Diego Museum of Natural History. Plate 37. Alaskan Coastal Scrub ( I3 r. r ). A thicket of what appears to be Sitka alder (A/nus sinuata) on Katmai National Monument, Alaska. U. S. National Park Service photo. Plate 38. Canadian Subpolar Scrub (13r.2) of scrub willows (Salix sp.) and willow ptarmigan (Lagopus lagopus) near Churchill, Manitoba, Canada. Photo taken in November 1988 by D. E. Brown. Plate 39. Alaskan Alpine and Subalpine Scrub (131.3) and grizzly bear (Ursus arctos) on the slopes of the Cathedral Mountains in Denali National Park and Preserve, Alaska, ca. 1400 m (4600 ft) elevation. Photo by D. E. Brown. 77 Plate 40. Rocky Mountain Alpine and Subalpine Scrub (r3r.4) . A "krum ho ltz" of limber pine (Pinus -fl,exilis) at an elevation of ca . 2000 m (6560 ft) on the east slope of the Rocky Mountains upslope from T he Nature Conservancy's Pine Butte Swamp Reserve ad jacent to the Lewis and Clark Nationa l Forest in Montana. Photo by D. E. Brown. Plate 4r. Casca de-Sierran Alpine and Subalpine Scrub (r3r.5) at an altitude of 2530 m (8300 ft) along the Pacific Coast Trail, Nevada Co unty, Ca liforni a. Photo taken by Richard E. Brown in July r99 5. Plate 42. Adirondack-Appalachian Alpine and Subalpine Scrub (13r.6) represented here by "Dwarf shrub heath communities" on the slopes of Mount Washington, New Hampshire, ca. 1375 m (4500 ft). The principal species present in these small patches of scrubland are Vaccinium uliginosum, V. vitisidaea, and Diapensia lapponica. Photo by Louella Brown. Plate 43. Madrean Alpine and Subalpine Scrub (13r.7) near the summit of Cerro Potosi, Nuevo Leon, Mexico, ca. 3650 m (12000 ft). Most of the shrubs are a prostrate species of pinyon pine (Pinus culminicola), which, as far as is known, is restricted to this mountain. Other subalpine associates include ]uniperus monticola, Senecio sanguisorbae, and Lupinus cacuminus (Beaman and Andresen 1966). Although minuscule in extent, this biotic community is the habitat for the endemic salamander Chiropterotriton priscus, and perhaps other animals. Photo by D. E. Brown. 79 Plate 44. Great Basin Montane Scrub (132.1) of Quercus gambelii in scrub-form at Raton Pass near the Colorado-New Mexico state line at an altitude of 23 50 rn (7700 ft). The two con ifers present are Rocky Mountain pinyon (Pinus edulis) and pond erosa pine (P. ponderosa). Photo by D. E. Brown. Plate 45. Madrean Montane Scrub (132.3) near the summit of the Sierra del Nido, Chihuahua, Mexico. This high-elevation (ca. 2460 m or 8100 ft) but fire-prone "chaparral" of shrubby oaks (Quercus sp.) and manzanita (Arctostaphylos sp.) is reminiscent of other cold temperate scrublands in the Cascade-Sierran (132.2) and Adirondack-Appalachian (132.4) biogeographic regions. Each of these montane scrublands comes with its own plant and animal components, however, and is biogeographically distinct. Photo by D. E. Brown. So Plate 46. Plains Deciduous Scrub (132.4) of shinnery oak (Quercus harvardi) within Plains Grassland at ca. 1130 m (3700 ft) altitude southeast of Roswell, Chaves County, New Mexico. Soi l Conservation Service photo taken by Max V. Hodson in 19 72. Plate 4 7. California Chaparral (133.1) comprised of several evergreen plant species in the San Bernardino National Forest, Riverside County, California, ca. 1220 m (4000 ft) altitude. Photo by C. E. Conrad. Sr Plate 48. California Coasta lscrub (133.2) of Ca li fo rni a Sagebrush (Artemisia californica), sages (Sa lvia spp.), Lemonade-berry (Rhus integrifolia), a nd other shrubs near Dana Point, Orange Co unty, Ca lifornia , altitud e ca. 50 m (160 ft). Because of urbanization a nd other disturbances, these "soft-chaparral" habitats are rapidly shrinki ng in extent. Photo by D. E. Brown. Plate 49. Southwestern Interior C haparra l (133.3) containing a shrub live oak (Quercus turbinella), desert ceanothus (Ceanothus greggii), Fremont mahoni a (Berberis fremontii), p ointlea f manzanita (Arctostaphhylos pungens), saca hui sta (No lina microcarpa), sugar sumac (Rhus ovata), and other shrubs on the Tonto National Forest, Gila County, Arizona, ca. 1600 m (5250 ft). U.S. Forest Service photo ta ken in r 9 3 5. Plate 50. Chihuahuan Interior Chaparral (133.4) at an altitude of 2150 m (7050 ft) in the Sierra La Leona, Nuevo Leon, Mexico. Present at this location are such characteristic chaparral plants as a shrub live oak (Quercus cordifolia?), mountain-mahogany (Cercocarpus mojadensis?), ceanothus (Ceanothus greggi?), algerita (Berberis trifoliata), manzanita (Arctostaphylos pungens), cliff-rose (Cowania plicata?), and skunkbush (Rhus trilobta). All but the last species are evergreen shrubs. A few junipers (]uniperus mexicanus?) and yuccas (Yucca carnerosa) are also present. Photo by D. E. Brown. Plate 5 r. Southeastern Maritime Scrub (13 3.5) on Jonathan Dickinson State Park north ofJupiter, Florida. These sterile dunes are sparsely clothed in a "chaparral-like" vegetation that here includes turkey oak (Quercus laevis) and Chapman oak (Q. chapmanii), rosemary (Ceratiola ericoides), and an occasional sand pine (Pinus clausa). Photo by D. E. Brown. Plate 52. Alaskan Grassland (14r.r) near Eielson Visitor Center, Denali Nationa r Park a nd Preserve, Alaska. The variety of herbaceous plants is large, and the forbs, many possessing showy flowers, greatly outnumber the bunchgrasses. Photo by D. E. Brown. Plate 53. Rocky Mountain Alpine and Subalpine Grassland (14r.2) at ca. 2800 m (9200 ft) on the Apache-Sitgreaves National Forest in Arizona's White Mountains. The most conspicuous grass is Thurber fescue (Festuca thurberi). Photo by D. E. Brown. Plate 54. Cascade-Sierran Alpine and Subalpine Grassland (14r.3) at an altitude of 2150 m (7050 ft) near Serene Lake, Nevada County, California. It is July, yet the snowpack has only recently melted, allowing the forbs and grasses to commence their annual growth. Swamp onion (Allium validum), ladies tresses (Spiranthes romanzoffiana), alum-root (Heuchera micrantha), yellow cinquefoil (Potentilla glandulosa), meadow hosackia (Lotus torreyi), wild hollyhock (Sidalcea reptens), cmv parsnip (Heracleum lanatum), meadow goldenrod (Solidago spp.), sneezeweed (Helenium bigelovii), and yellow milfoil (Achillea millefolium) are just a few of the many species of flowers likely to be present. Photo taken in 199 5 by Richard E. Brown. Plate 55. Transvolcanic Alpine and Subalpine Grassland (14r.6). This is the "zacatonal" habitat of the volcano rabbit (Romeralagus diazi). Important "zacaton" grasses include Muhlenbergia macroura, Festuca rosei, F. amplissima, and Stipa ichu (Fa and Bell 1990). The snow-capped peak in the background is 5452 m (17888 ft) Volcan Popocatepetl southeast of Mexico City. Photo by Alejandro Velazquez. Plate 56. Plains Grassland (142.1). A southern extension of a "mid-grass" prairie community at an altitude of ca. l 67 5 m ( 5 500 ft) near El Sueco Junction, Chihuahua, Mexico. The principal species is sideoats grama (Bouteloua curtipendula), but B. gracilis, Andropogon gerardii, Sporobolus heterolepis, and Schizachyrium scoparium are also present as are numerous forbs. Photo by D. E. Brown. Plate 57. Great Basin Shrub-Grassland (142.2) dominated by bluebunch wheatgrass (Agropyron spicatum) near Kalotus, Franklin County, Washington. Soil Conservation Service photo by Claude C. Dillon. 86 Plate 58. Oregonian (Pacific Coastal) Grassland (142.3) near Salishaw, Oregon, a "wet-meadow" populated principally by Pacific reedgrass (Calamagrostis nutkaensis). Photo by D. E. Brown. Ｚｾ＠ Plate 60. Cascade-Sierran Montane Grassland (142.5) at an altitude of ca. 2135 m (7000 ft) near La Grulla in the Sierra San Pedro Martir, Baja California Norte, Mexico. Photo taken by E. A. Goldman in July 1905. Although heavily cropped by livestock, these meadow grasslands appear to have remained largely unchanged seventy-five years later. :.__··:-:..( :::..:..:.!::\.., ｾﾷ＠ｾＢＺ＠Ｍｾﾷ＠ M. •, ·;.-i.,. ..., ［ｾﾷ＠ ,,,,- ... ,.,,._ ,1. ' Plate 6r. Chihuahuan (Semidesert) Grassland (143.1) at an altitude of 1465 m (4800 ft) in Sulphur Springs Valley, Cochise County, Arizona. The spiky-appearing shrubs are "palmilla" (Yucca elata) and the dominant grass is blue grama (Bouteloua gracilis). Such landscapes occupy large tracts of southeastern Arizona, southern New Mexico, southwest Texas, and north-central Mexico. Other Semidesert Grassland communities are more complex, and Semidesert Grassland is an appropriate and convenient designation for a broad spectrum of ecotone and transition communities found between desertscrub and scrubland. Photo by D. E. Brown. 88 Plate 62. Ca lifornia Valley Grassland (143.2) west of Crow's Landi ng, Stanislaus Co unty, Ca li fo rnia, ca. 75 rn (250 ft) a ltitude. The vegetation is almost entirely introduced ann ua l forbs of the genu s Erodium and suc h a nnu a l a li en grasses as Bromus and Avena. Soil Conservation Service photo taken by M. W. Talbot in 1934· Plate 63. Gu lf Coasta l Grassland (143.3) at an a ltitude of ca. 60 m (200 ft) o n Attwater Prairie Chicken National Wildlife Refuge, Colorado County, Texas. The grass cover is both dense and diverse, and includ es such characteristic species as G ulf muhly (Muhlenbergia capillaris) , little bluestem (Schizachyrium scoparium), big blu estem (Andropogon gerardii), broomsedge bluestem (A. virginicus), switchgrass (Panicum virgatum), and Indiangrass (Sorghastrum nutans) . Photo taken in February, 199 5, by Jenny Hoskins. Plate 64. Great Basin Desertscrub (152.1) on the Desert Experimental Range in Utah. The dominant plants are winterfat (Eurotia lanata) and shadscale (Atriplex confertifolia). U.S. Forest Service photo taken in 1951 by Selar S. Hutchings. Plate 65. Mohave Desertscrub (153.1) at ca. 1125 m (3700 ft) altitude in Yavapai County, Arizona. Besides such endemic indicators as Joshua-tree (Yucca brevifolia) and goldenhead (Acamptopappus sphaerocephalus), prevalent plants in this southeastern outlier of the Mohave Desert include creosotebush (Larrea tridentata), catclaw acacia (Acacia greggi), and beavertail cactus (Opuntia basilaris). Photo by D. E. Brown. Plate 66. Chihuahuan Desertscrub (153.2). This "foothill" or mixed succul ent-scrub community at 825 m (2700 ft) altitude on the slopes of the Sierra San Marcos, Coa huila, Mexico, contains a diverse assemblage of plants that include Yucca macrocarpa, Dasylirion leiophyllum, Agave lecheguilla, Hechtia spp., Opuntia leptocaulis, Euphorbia antisyphilitica, Leucophyllum frutescens, Fouquieria splendens, Larrea tridentata, and Dyssodia petachaeta. Photo by D. E. Brown. Plate 67. Central American Paramo (3,11r.1) at an altitude of ca. 3200 m (10500 ft) in the Sierra Talmanaca, Costa Rica. Saint John 's wort (Hypericum spp.) and dwarf bamboos (Chusquea spp.) are among the "chaparral-like" plants that dominate this above-timberline vegetation. Photo by Charlotte M. Christy in July 1994· Plate 68. Central American Cloud Forest (124.1) at an altitude of 1600 rn (5250 ft) on the Monte Verde Reserve in Costa Rica's Cordillera de Tilaran. This 30 to 40 rn tall, evergreen forest straddles both the Atlantic and Pacific drainages, and is represented by Nearctic trees belonging to the beech, myrtle, and laurel families as well as such tropical genera as Ficus, Sapium, and Cecropia. Photo by D. E. Brown. Plate 69. Central American Evergreen Rain Forest (124.2) on the La Selva Biological Reserve, Heredia Province, Costa Rica. Almost 90 percent of this lowland reserve is virgin forest in which the leguminous "Gavilan" (Pentaclethra macroloba), and various dwarf palms are important participants. Photo by D. E. Brown. 92 Plate 70. Central American Semi-Evergreen Forest (124.3) at ca. 300 m (985 ft) altitude on Parque Nacional Santa Rosa, Guanacaste Province, Costa Rica. It is March toward the end of the dry season, and the evergreen trees in the more protected locales stand in marked contrast to their deciduous associates. Photo by D. E. Brown. Q . Plate 7r. Central American Dry Forest (124.4) at Rancho La Pacifica, Guanacaste Province, Costa Rica. The drought-deciduous aspect of the forest is obvious in March 1983. Photo by D. E. Brown. 93 Plate 72. Campechian Montane Evergreen Forest (124.5) at an altitude of ca. 400 m (1300 ft) in the mountains above the Maya ruins near Palengue in Chiapas, Mexico. Note the variation in tree trunk forms. Photo by D. E. Brown. Plate 73. Campechian Semi-Evergreen Forest (124.6) near Coba, Quintana Roo, Mexico, in March 1985. Photo by D. E. Brown. 94 Plate 74. Yucatan Semi-Deciduous Forest (124.7) near Kabah, Yucatan, Mexico. Note the bromeliad (Tillandsia recurvata) growing on the tree branches. Photo taken in March 1993 by D. E. Brown. Plate 75. Yucatan Dry Deciduous Forest (124.8) near Mayapan, Yucatan, Mexico. Note the scrubby understory and the co lumnar cacti. Photo by D. E. Brown. 95 Plate 76. Guerreran Dry Deciduous Forest (124.9) at ca. rroo m (3600 ft) altitude in the lower Tehuacan Valley near the borders of Oaxaca and Puebla, Mexico. In addition to "pochote" (Ceiba aesculifolia), the trees include "copal" and other species of Bursera. Photo by D. E. Brown. Plate 77. Veracruz Evergreen Rain Forest (124.1a) at ca. loom (300 ft) altitude near Santa Lucrecia, Veracruz, Mexico. Some of th e forest's trees appear to have been cut down, thus favoring the development of a dense secondary forest. Photo taken in Janu ary 1904 by E. A. Goldman. Plate 78. Veracruz Semi-Evergreen Forest (124.1b) at an altitude of ca. 800 m (2625 ft) in the mountains east of Gomez Farias, Tamaulipas, Mexico. Immediately above this site one encounters Veracruz Cloud Forest. Important if not characteristic trees present at this locality include Bursera simarubra, Cecropia obtusifolia, and Brosimum alicastrum. Photo by D. E. Brown. Plate 79. Nayarit-Guerreran Semi-Evergreen Forest (124.1c) south of Acaponeta, Nayarit, Mexico. These diverse and beautiful forests are rapidly being converted to agriculture on all but the steepest slopes. Photo by D. E. Brown. 97 Plate So. Sinaloan Dry Deciduous Forest (124.1d) during the leafless season in December at ca. 500 m (1640 ft) altitude southeast of Alamos, Sonora, Mexico. The canopy of leguminous trees overtops the columnar cacti which are mostly hechos (Pachyereus pecten-aboriginum). Photo by D. E. Brown. Plate Sr. Tamaulipan Semi-Deciduous Forest (124.1e) at an altitude of ca. 550 rn (1S oo ft) in the Sierra Tamalare between Ocampo and Tula, Tamaulipas, Mexico. The light-colored plants in the center right of the photograph are flowering soyate (Dasylirion langissimum), one of several "indicator species" for this biotic community. Photo by D. E. Brown. Plate 82. San Lucan Dry Deciduous Forest (124.rf) at its lower limits near La Palmilla in the Cape region of Baja Ca li fornia Sur, Mexico. The white-barked trees are Lysiloma candida. Other species present are Bursera microphylla, Karwinsikia humboldtiana, Cercidium peninsulare, Pithecellobium confin e, and Pachycereus pringlei. Photo taken by]. R. Hastings in 194r. Plate 83. Caribbean C loud and Montane Evergreen Forest (r 24. rg) on the slopes of the Sierra Luquillo in the El Yunq ue Recreation Area of the Caribbea n National Forest, Puerto Rico . T he presence of tree ferns helps distinguish these higher eleva tion forests from lower, coastal evergreen fores ts. Photo by D. E. Brow n. 99 Plate 84. Caribbean Lowland Evergreen Forest (124.1 h) on Luquillo Beach, Puerto Rico. Although groves of the widely planted and naturalized coconut palm (Cocos nucifera) now almost exclusively dominate many Caribbean beaches, other lowland sites are populated by pines (e.g., Pinus caribaea) and/or other evergreen trees. Photo by D. E. Brown. Plate 85. Caribbean Dry Forest (124.1i) on the southeast coast of the island nation of Dominica. It is January, the rainy season is ending, and trees such as gumbo limbo (Bursera simaruba) are beginning to shed their leaves. Photo by D. E. Brown. 100 Plate 86. Floridian Evergreen (Hammock) Forest (124.1j). A "hammock" community preserved in Red Reef Park within the city of Boca Raton, Florida. Just a few of the tree species present at this site, which is just above sea-level, are gumbo limbo (Bursera siinaruba), strangler fig (Ficus aurea), poisonwood (Metopiuin toxiferuin), inkwood (Exothera paniculata), leadwood (Krugiodendron ferreuin), and pigeon plum (Coccoloba diversifolia). Most are evergreen and many are restricted to southern Florida and the West Indies. Photo by D. E. Brown. Plate 87 . Guerreran Thornscrub (134.1) in the Rio Atoyac Valley, Puebla, Mexico. Unlike columnar cacti in tropical deciduous forests, the candelabra-like cactus (Leinaireocereus weberi) protrudes above a diverse scrubland of shrubby trees, bushes, and smaller cacti. Photo by D. E. Brown . . - IOI Plate 88. Sinaloan Thornscrub (I34.2) in the Sierra Frent6n between Rayon and Carbo, Sonora, Mexico, at an altitude of ca. 600 m (I970 ft). The shrubbery is diverse and includes such species as tree-ocotillo (Fouquieria macdougalii), hopbush (Dodonaea viscosa), Caesalpinia pumila, mesquite (Prosopis juliflora), organ-pipe cactus (Stenocerus thurberi), and a paloverde (Cercidium microphyllum). Photo by D. E. Brown. Plate 89. Tamaulipan Thornscrub (I34.3) along the lower Rio Grande between Eagle Pass and Laredo, Texas, ca. 260 m (8 50 ft) altitude. Included within this landscape are such plants as mesquite (Prosopis glandulosa), Texas ranger or "cenizo" (Leucophyllum frutescens), several acacias (Acacia spp.), and prickly-pear cacti (Opuntia spp.). Recently semidesert grassland, this "brush country," called "chaparral" in Texas, is best biogeographically described as thornscrub. Photo by D. E. Brown. I02 Plate 90. San Lucan Thornscrub (134.4) at ca. 75 m (250 ft) altitude near Cabo San Lucas, Baja Ca lifornia Sur, Mexico. The number of participating plants is large and includes ]atropha cinerea, Bursera microphylla, Machaerocereus gummosus, and Solanum hindsianum-all of which are overtopped by Pachycereus pringlei. Photo by]. R. Hastings. 103 Plate 92. Central American Thornscrub (134.6) near Comayagua, Honduras. The shrubbery is punctuated by a columnar cactus, a cholla, and an arborea l prickly-pear, as well as numerous small trees. Photo by D. E. Brown. Plate 93. Central American Savanna Grassland (144.1) on Santa Rosa National Park, Guanacaste Province, Costa Rica. The principal grass is said to be " jaragua" (Hyparrahenia rufa) , a pasture grass introduced from Africa. The debate over whether Central American savannas are " natural " or "maintained" is now largely moot given the widespread and frequent occurrence of both natural and man-induced fires in this type of vegetation. Photo by D. E. Brown. 104 Plate 94. Guerreran Savanna Grassland (144.2) off Mexican Highway 190 near Huajuapan de Leon, Oaxaca, Mexico. The trees are mostly the sombrero palm (Brahea dulcis) with some "nance" (Byrsonima crassifolia) and "raspaviejo" (Curatella americana) present. The grasses include both Nearctic and Neotropical genera, e.g., Bouteloua and Cynodon. Photo by D. E. Brown. Plate 95. Campechian-Veracruz Savanna Grassland (144.3) near the Campeche-Tabasco border in Mexico. The factors determining the presence of savanna vegetation in the tropics are complex and involve soil moisture and composition, seasonal drought, landscape physiognomy, fire frequency, and human history (Borhidi 1991). Photo by D. E. Brown. 105 Plate 96. Caribbean Savanna Grassland (144.4) in Mayaguez District, Puerto Rico. The trees are mesquites (Prosopis sp.). Tropical grasslands or savannas can be found in all Neotropical biotic provinces, each having its own peculiarities and constituents. Photo by D. E. Brown. Plate 97. Sonoran Savanna Grassland (144.5) at 610 m (2000 ft) altitude south of Benjamin Hill, Sonora, Mexico. The principal grasses are Rothrock grama (Bouteloua rothrockii) and threeawns (Aristida spp.); the trees are mesquite (Prosopis velutina), paloverdes (Cercidium microphyllum, C. floridum), and ironwood (Olnea tesota). The shrub in the immediate center is a young acacia (Acacia angustissima). This area has since been increasingly invaded by scrub. Photo taken by Roy E. Tomlinson in the summer of 1968. 106 Plate 98. Tamaulipan Savanna Grassland (144.6) ju st northeast of the Ca ll es railroad station in Tamau li pas, Mexico, ca. 400 m (1300 ft). The pri ncipal grass is a species of Cynodon which occurs with several genera of both tropical and temperate origin. Photo by D. E. Brown. Plate 99. Sonoran Desertscrub (154.1). This and the following figure show two extreme views. This photograph was ta ken in the foot hills of the Sierra de los Mochos in Sonora, Mexico, at an a ltitude of ca. 300 rn (9 8 5 ft). Four species of columnar cacti (Pachycereus pringlei, Stenocereus thurberi, Lophocereus schotii, and Carnegia gigantea) are visible in this landscape. About the on ly species common to both loca liti es is blu e paloverde (Cercidium floridum). Photo by D. E. Brown. 107 Plate roo. Sonoran Desertscrub (154.1). This photograph was taken in the dunefie ld s near Glamis, Ca liforni a, at an altitude of ca. 50 m (160 ft). See plate 99 for con trast. Photo by D. E. Brown. Plate ror. Arctic Wet Tundra (21r.). It is springtime in this Alaskan Wet Tundra biotic community within Alaska's Colville River Delta, the ground and ponds above the permafrost have thawed, and the marsh marigold (Coetha palustrus) is in bloom. U. S. Fish and Wildlife Service photo taken by Urban C. Nelson. ro8 Plate 102. Boreal Swamp and Riparian Forest (22r.). Both Canadian Swamp Forest and Canadian Swamp Scrub biotic communities are represented in this U.S. Fish and Wildlife Service photo taken by Charles D. Evans east of Bearhead Lake in Manitoba, Canada. The dark trees are primarily black spruce (Picea inariana) accompanied by willows (Salix sp.) and alders (A/nus sp.). Plate io3. Cold Temperate Swamp and Riparian Forest (222.). This particular Northeastern Riparian Forest along the Des Moines River Valley in Iowa is composed largely of Eastern cottonwood (Populus deltoides) and silver maple (Acer saccharinuin). U.S. Forest Service photo taken in July 1945 by A. L. McComb. 109 Plate 104. Warm Temperate Swamp and Riparian Forest (223.). Baldcypress (Taxodium distichum) almost exclusively occupies this Southeastern Swamp Forest in North Carolina. U.S. Forest Service photo taken by W. H. Shaffer in May 1940. Plate 105. Arctic-Boreal Swamp Scrub (23r.). A small area of Rocky Mountain Subalpine Swamp Scrub above 2600 m (8 500 fr) within the Phelps Botanical Area of the Apache-Sitgreaves National Forest in Arizona. The shrubbery appears to be composed chiefly of Bebb willow (Salix bebbiana) and red-osier dogwood (Cornus stolonifera) with some thin-leaf alder (A/nus tenuifolia) also present. Photo taken by Rex King in September 194 5. IIO Plate ro6. Cold Temperate Swa mp and Riparian Sc rub (232.). Willows (Sa lix spp.) are the principal plants making up this Rocky Mountai n Riparian Scrub a long the headwaters of the Snake River in Teton Co unty, Wyoming. Note the sedge meadow (Rocky Mountain Mars hl and) in the center of the photo a nd the island of Rocky Mountai n Swamp Forest. Photo by D. E. Brow n . ._tl: Plate ro7. Warm T emperate Swamp and Riparian Scrub (233.). A California Maritime Swamp Scrub of pickleweed (Salicornia virginica) and other halophytes in southern San Francisco Bay, Santa Clara County, Californi a. Photo by D . E. Brown. III Plate Io8. Arctic-Boreal Marshland (24r.). A tiny sedge-populated cienega of Rocky Mountain Subalpine Marshland located at 2740 m (9000 ft) atop the Pinalei'io Mountains, Graham County, Arizona. Photo by D. E. Brown. Plate ro9. Cold Temperate Marshland (242. ). A Great Basin Marshland located at Ruby Lake, Elko County, Nevada. The principal marsh remergents .are rnundstem bulrush (Scirpus acutus) and cattaii.l (Typha latifOJlia). Photo by D. E. Brown. II2 Plate IIO. Warm Temperate Marshland (243.). This U.S. Fish and Wildlife Service photograph by George C. Moore of the mouth of the Satilla River in Georgia shows a Southeastern Maritime Marshland of needlegrass (]uncus roemerianus). Plate III. Arctic-Boreal Strand (25r.) of bare gravel and melted ice left by a receding glacier in Olympic National Park, Washington. U.S. National Park Service photo by George A. Grant. 113 Plate 112. Cold Temperate Strand (252.). A U.S. Park Service photo of Oregonian Maritime Strand taken in February 1961 by Louis G. Kirk at Rialto Beach, Olympic National Park, Washington. Plate 113. Warm Temperate Strand (253.) represented by California Maritime Strand at Scammon's Lagoon, Baja California Norte, Mexico. This sparsely vegetated community on a mud substrate, although a true wetland, is reminiscent of, and analogous to, the desertland formation of upland vegetation. A stand of cordgrass (Spartina sp.) forms a marshland in the background. Photo by D. E. Brown. 114 Plate 114. Tropical-Subtropical Swamp, Riparian, a nd Oasis Forest and Woodland (3,224.). This and the following figure illustrate the diversity of these biotic communities. This photograph shows a Yucata n Maritime Swamp Forest of mangroves (mostly Rhizophora mangle) near Cel ustun, Yucatan, Mexico. Photo by D. E. Brown. Plate 115 . Tropical-Subtropical Swamp, Riparian, and Oasis Forest and Woodland (3,224.). This photograph illustrates a Sonoran Riparian Forest of California fan palms (Washingtonia filifera) within the Sonoran Desert near Wickenburg, Arizona . Photo by D. E. Brown. See also plate l 14. rr5 Plate 116. Tropical-Subtropical Swamp and Riparian Scrub (2 34.) . A Sonoran Swamp Scrub of the adventive saltcedar (Tamarix parviflora) in the delta of the Colorado River in Baja California Norte, Mexico. Photo by D. E. Brown. Plate 117. Tropical-Subtropical Marshland (244.). A Caribbean Interior Marshland (foreground) surrounds an etang or pond within Evergreen Forest on Guadeloupe Island's spacious Pare Nature!. Photo by D. E. Brown. II6 \, 1 Plate u8. 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