Unclassified
ENV/JM/MONO(2008)30
Organisation de Coopération et de Développement Economiques
Organisation for Economic Co-operation and Development
28-Nov-2008
___________________________________________________________________________________________
English - Or. English
ENVIRONMENT DIRECTORATE
ENV/JM/MONO(2008)30
Unclassified
JOINT MEETING OF THE CHEMICALS COMMITTEE AND
THE WORKING PARTY ON CHEMICALS, PESTICIDES AND BIOTECHNOLOGY
SERIES ON HARMONISATION OF REGULATORY OVERSIGHT IN BIOTECHNOLOGY
Number 43
CONSENSUS DOCUMENT ON THE BIOLOGY OF DOUGLAS-FIR (Pseudotsuga menziesii (Mirb.)
Franco)
English - Or. English
JT03256472
Document complet disponible sur OLIS dans son format d'origine
Complete document available on OLIS in its original format
ENV/JM/MONO(2008)30
OECD Environment, Health and Safety Publications
Series on Harmonisation of Regulatory Oversight in Biotechnology
No. 43
Consensus Document on the Biology of Douglas-Fir (Pseudotsuga
Menziesii (Mirb.) Franco
Environment Directorate
Organisation for Economic Co-operation and Development
Paris 2008
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PREAMBLE
The environmental safety/risks of transgenic organisms are normally based on the information on the
characteristics of the host organism, the introduced traits, the environment into which the organism is
introduced, the interaction between these, and the intended application. The OECD’s Working Group on
Harmonisation of Regulatory Oversight in Biotechnology decided at its first session, in June 1995, to focus
its work on identifying parts of this information, which could be commonly used in countries for
environmental safety/risk assessment to encourage information sharing and prevent duplication of effort
among countries. Biosafety Consensus Documents are one of the major outputs of its work.
Biosafety Consensus Documents are intended to be a “snapshot” of current information on a specific
host organism or trait, for use during regulatory assessments. They are not intended to be a comprehensive
source of information on everything that is known about a specific host or trait; but they do address the key
or core set of issues that member countries believe are relevant to risk/safety assessment. This information
is said to be mutually acceptable among member countries. To date, 29 Biosafety Consensus Documents
have been published. They include documents which address the biology of crops, trees and microorganisms as well as those which address specific traits which are used in transgenic crops.
In reading the Consensus Documents, it is useful to consult two additional texts. The first, entitled An
Introduction to the Biosafety Consensus Document of OECD’s Working Group for Harmonisation in
Biotechnology explains the purpose of the Consensus Documents and how they are relevant to risk/safety
assessment. It also describes the process by which the documents are drafted using a “lead country”
approach. The second text is Points to Consider for Consensus Documents on the Biology of Cultivated
Plants. This is a structured checklist of “points to consider” for authors when drafting or for those
evaluating a Consensus Document. Amongst other things, this text describes how each point is relevant to
risk/safety assessment.
The Consensus Documents are of value to applicants for commercial uses of transgenic organisms,
regulators in national authorities as well as the wider scientific community. As each of the documents may
be updated in the future as new knowledge becomes available, users of Consensus Documents are
encouraged to provide any information or opinions regarding the contents of this document or indeed,
OECD’s other harmonisation activities. If needed, a short pre-addressed questionnaire is attached at the
end of this document that can be used to provide such comments.
The published Consensus Documents are also available individually from OECD’s website
(http://www.oecd.org/biotrack) at no cost.
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ENV/JM/MONO(2008)30
FOREWORD
Consensus Documents contain information for use during the regulatory assessment of a particular
product. In the area of plant biosafety, these are being published on information on the biology of certain
plant species, selected traits that may be introduced into plant species, and biosafety issues arising from
certain general types of modifications made to plants.
This document addresses the biology of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Canada
served as the lead country in the preparation of this document. The draft was revised on a number of
occasions based on the inputs from other member countries. This document is published on the
responsibility of the Joint Meeting of the Chemicals Committee and the Working Party on Chemicals,
Pesticides and Biotechnology of the OECD.
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TABLE OF CONTENTS
ABOUT THE OECD ...................................................................................................................................... 6
FOREWORD .................................................................................................................................................. 7
PREAMBLE ................................................................................................................................................. 10
SUMMARY NOTE ...................................................................................................................................... 11
SECTION I. TAXONOMY .......................................................................................................................... 11
SECTION II. NATURAL DISTRIBUTION ................................................................................................ 12
SECTION III. REPRODUCTIVE BIOLOGY ............................................................................................. 13
A. Reproductive development ................................................................................................................... 13
B. Mating system and gene flow ............................................................................................................... 14
C. Seed production .................................................................................................................................... 14
D. Natural regeneration ............................................................................................................................. 15
E. Vegetative reproduction ........................................................................................................................ 16
SECTION IV. GENETICS ........................................................................................................................... 18
A. Cytology ............................................................................................................................................... 18
B. Genetic variation................................................................................................................................... 18
C. Inbreeeding depression and genetic load .............................................................................................. 21
SECTION V. HYBRIDISATION ................................................................................................................ 22
SECTION VI. ECOLOGY ........................................................................................................................... 23
A. Autecology ........................................................................................................................................... 23
B. Synecology ........................................................................................................................................... 26
C. Stand dynamics ..................................................................................................................................... 27
D. Damaging agents .................................................................................................................................. 28
SECTION VII. FORESTRY PRACTICES .................................................................................................. 30
A. Deployment of reforestation materials ................................................................................................. 30
B. Provenance transfer .............................................................................................................................. 30
C. Breeding programs ............................................................................................................................... 31
D. Conservation of genetic resources ........................................................................................................ 32
SECTION VIII. SUMMARY ....................................................................................................................... 34
SECTION IX. REFERENCES ..................................................................................................................... 35
QUESTIONNAIRE TO RETURN TO THE OECD .................................................................................... 51
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Tables
Table 1.
Table 2.
Genetic diversity and population differentiation estimates for Douglas-fir.......................... 20
Examples of individual heritability estimates for quantitative traits in Douglas-fir ............. 21
Figures
Figure 1. The main native range of Douglas-fir ................................................................................... 12
Figure 2. Douglas-fir site index relative to soil moisture and soil nutrient regimes in a dry, cool
mesothermal climate of coastal British Columbia, Canada ...................................................................... 24
Figure 3.
Edatopic grid showing pre-treatment foliar nitrogen and sulphate-sulphur, and isolines of
relative basal-area response, indicating 3rd-year response of Douglas-fir to nitrogen fertilisation .......... 25
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SECTION I. TAXONOMY
Pseudotsuga menziesii (Mirbel) Franco is generally called Douglas-fir (so spelled to maintain its
distinction from true firs, the genus Abies). Pseudotsuga Carrière is in the kingdom Plantae, division
Pinophyta (traditionally Coniferophyta), class Pinopsida, order Pinales (conifers), and family Pinaceae.
The genus Pseudotsuga is most closely related to Larix (larches), as indicated in particular by cone
morphology and nuclear, mitochondrial and chloroplast DNA phylogenies (Silen 1978; Wang et al. 2000);
both genera also have non-saccate pollen (Owens et al. 1981, 1994). Based on a molecular clock analysis,
Larix and Pseudotsuga are estimated to have diverged more than 65 million years ago in the Late
Cretaceous to Paleocene (Wang et al. 2000). The earliest known fossil of Pseudotsuga dates from 32 Mya
in the Early Oligocene (Schorn and Thompson 1998).
Pseudostuga is generally considered to comprise two species native to North America, the widespread
Pseudostuga menziesii and the southwestern California endemic P. macrocarpa (Vasey) Mayr (bigcone
Douglas-fir), and in eastern Asia comprises three or fewer endemic species in China (Fu et al. 1999) and
another in Japan. The taxonomy within the genus is not yet settled, and more species have been described
(Farjon 1990). All reported taxa except P. menziesii have a karyotype of 2n = 24, the usual diploid number
of chromosomes in Pinaceae, whereas the P. menziesii karyotype is unique with 2n = 26. The two North
American species are vegetatively rather similar, but differ markedly in the size of their seeds and seed
cones, the latter 4-10 cm long for P. menziesii and 9-20 cm for P. macrocarpa (Elias 1980; Lipscomb
1993). Although additional species have been described that may occur in Mexico (Flous 1934a, 1934b;
Martínez 1963) — P. flahaultii Flous, P. guinieri Flous, P. lindleyana (Roezl) Carr., P. macrolepis Flous,
P. rehderi Flous, these taxa are not broadly recognized due to their overlapping morphological characters
which do not correlate with the scattered distribution of Mexican populations of the genus (Farjon 1990;
Debreczy and Rácz 1995; Reyes-Hernández et al. 2005). Considerable morphological variation has been
found among 19 populations sampled from the three major geographical regions of Mexico where
Pseudotsuga occurs (Reyes-Hernández et al. 2005). Strong genetic differentiation for isozymes was found
between a northeastern Mexican population of P. menziesii at approximately 25º N (2500 m elevation) and
103 other populations of the species sampled rangewide (Li and Adams 1989).
Two botanical varieties of Douglas-fir are commonly recognized: P. menziesii var. menziesii, called
coastal Douglas-fir, and P. menziesii var. glauca (Beissner) Franco, called Rocky Mountain or interior
Douglas-fir (Little 1979; Lipscomb 1993). The two varieties may intergrade in interior British Columbia
(Canada) but have geographically separate ranges to the south. The varieties differ in many morphological,
physiological and ecological characteristics. The coastal variety has greenish needles and longer seed
cones with straight, appressed bracts, whereas the interior variety has bluish-green needles and shorter
cones with reflexed bracts. Although the differences are not always obvious, strong differentiation of these
varieties has been confirmed with isozymes, and nuclear, mitochondrial, and chloroplast DNA studies (Li
and Adams 1989; Aagaard et al. 1995, 1998a, 1998b; Klumpp 1999; Nelson et al. 2003). Some of these
studies have also indicated strong differentiation between the northern and southern subgroups of
P. menziesii var. glauca. Literature particularly from Europe (e.g. Göhre 1958; Klumpp 1999) sometimes
recognizes another interior variety for the northern half of the continental range, P. menziesii var. caesia
(Schwerin) Franco. Recently an additional variety, P. menziesii var. oaxacana Debreczy & Rácz, has been
proposed for a few stands of narrow columnar trees with grayish foliage and small cones at the
southernmost extent of the species’ range (Debreczy and Rácz 1995; Acevedo-Rodríguez 1998).
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SECTION II. NATURAL DISTRIBUTION
Douglas-fir is a common western North American species (central to southern area in both the Pacific
and the Cordilleran regions), with a very broad latitudinal range extending from 55º N (Klinka et al. 2000;
Hermann and Lavender 1990) to 16º N (Debreczy and Rácz 1995; Reyes-Hernández et al. 2005)
(Figure 1). The coastal variety occurs from central British Columbia southward primarily along the Pacific
Coast for about 2200 km to 34º44' N, reaching mid-California in the coastal Santa Cruz Mountains yet also
occurring inland in the northern Sierra Nevada (Lipscomb 1993). The range of the continental interior
variety extends along the Rocky Mountains into the mountains of southern Mexico over a distance of more
than 4500 km. In northeastern Oregon, and southern Idaho southward through the mountains of eastern
Nevada, Utah, Colorado, Arizona, New Mexico, western Texas and into Mexico, the distribution is
discontinuous and fragmented. Disjunct populations are present in Alberta and the eastern-central parts of
Montana and Wyoming (Hermann and Lavender 1990; Lipscomb 1993), and as far to the south as 16º22' N
in central Oaxaca (Debreczy and Rácz 1995).
Figure 1. The main native range of Douglas-fir
Source: Hermann and Lavender 1990
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SECTION III. REPRODUCTIVE BIOLOGY
A. Reproductive development
Douglas-fir is monoecious. Trees commonly reach reproductive maturity at 12 to 15 years of age.
Primordia of undifferentiated buds are already present when vegetative buds flush in the spring of the year
preceding the cone crop (Hermann and Lavender 1990). By mid-June, vegetative bud primordia, pollen
cone primordia (usually clustered near the base of the extending shoot), and seed cone primordia (borne
singly near the tip of the shoot) (Allen and Owens 1972) can be separated based on histochemical
differences.
The number of lateral buds initiated that differentiate into reproductive buds, rather than aborting or
developing into vegetative buds, determines the potential size of the cone crop. Poor seed cone crops in
part reflect a high abortion rate of buds during the preceding summer. Large numbers of pollen cone buds
or seed cone buds in the fall merely indicate the potential for a heavy cone crop the following year, as
buds, cones and seeds can subsequently be damaged by frost and cones and seeds can be damaged or
destroyed by seed predation before they mature (Dobbs et al. 1974).
Male strobili (pollen cones), generally abundant on year-old shoots especially in the lower crown, are
about 2 cm long and yellow to deep red. Their overlapping microsporophylls each have two abaxial
microsporangia (pollen sacs), which contain pollen mother cells that undergo meiosis and produce a tetrad
of microspores. Each microspore develops into a mature, five-celled pollen grain containing two prothalial
cells, a sterile (traditionally “stalk”) cell, a generative (or “body”) cell and a tube cell (Allen and Owens
1972; Fernando et al. 2005). The mature pollen grains are spherical when hydrated but dry and bowlshaped when shed, have a seemingly smooth exine, and are rather large (90-110 µm diameter), so they do
not disperse as far as the pollen of some conifers (Owens 1973; Tsukada 1982; Jackson and Smith 1994;
Fernando et al. 2005). Under typical weather conditions most pollen is dispersed within ten tree heights,
although small amounts can disperse over much greater distances when winds are strong. Pollen dispersal
occurs for 20 to 30 days in a stand (Silen 1963).
Female strobili (seed cones), occur on year-old lateral shoots usually in the upper half of the crown.
They are about 3 cm long, deep green to deep red, and have distinctive narrow trident bracts projecting
from between the cone scales. The young cones are erect, and receptive to pollination when emerged
(especially halfway or more) from the bud scales, i.e. at bud burst, and on average for 6-8 days (Webber
and Painter 1996; Stein and Owston 2002). Anthesis and pollination of the coastal variety occur during
March and April in warmer areas and as late as May or early June in colder areas. Pollen lands on the
bracts and moves downward to the ovuliferous scales and inward to the apices of the inverted ovules
(Takaso and Owens 1995). The cones then become larger and pendant, with the cones scales appressed.
Pollen collects on hairs of the integument’s bilobed stigmatic tip, which then collapses inward to
bring pollen into the micropyle (Allen and Owens 1972; Webber and Painter 1996). Fertilisation occurs
about 10 weeks after pollination. Pseudotsuga and Larix have delayed ovular secretion, with a postpollination pre-fertilisation drop filling the micropylar canal 5-7 weeks after pollination (von Aderkas and
Leary 1999; Gelbart and von Aderkas 2002; Poulis et al. 2005). This drop is thought to assist the pollen
grain in reaching the ovule and preparing for germination. The generative (body) cell of the pollen grain
divides to produce two male gametes prior to fertilisation. After approximately 2 weeks, pollen grains
germinate and pollen tubes grow into archegonia, releasing the two male gametes, one of which will
fertilise the egg cell. Ovules contain four to six archegonia, thus multiple fertilisations and polyembryony
occur, although typically only one embryo survives to maturity (Allen and Owens 1972). The embryo is in
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a cavity surrounded by the firm, cream-coloured, haploid megagametophyte which forms multinucleate
storage cells, thus serving as a food reserve for the germinating embryo (Owens 1973; von Aderkas et al.
2005a). Each ovuliferous scale can produce two seeds at its base. Each seed (with the seed coat 5-7 mm
long) has a large wing (twice to thrice the body length) consisting of two cell layers derived from the
ovuliferous scale. Mature seeds are dark brown on one side and mottled light brown on the other.
At low and middle elevations, cones mature and seeds ripen from mid-August to mid-September. The
bracts turn brown when seeds are mature. Cone scales reflex and seedfall occurs under dry conditions soon
after cone maturity, with two-thirds of the total crop typically on the ground by the end of October.
Remaining seeds fall during the winter and spring. Reproductive phenology is similar for the interior
variety (Baumgartner and Lotan 1991). The degree of dormancy of mature seed and thus the amount of
chilling required to break it varies geographically. Chilling requirements are met over the winter and
dormancy broken naturally. Dormancy is broken artificially through cold stratification; seeds are soaked in
water for 24 hours, then chilled at 2 to 5oC, usually for 21 days. Coastal Douglas-fir generally requires cold
stratification, whereas northern Rocky Mountain Douglas-fir may benefit from stratification and southern
provenances may not. After dormancy is broken, seed will germinate at temperatures ranging from 10 to
30oC. There is no light requirement for germination. The viability of seed can be maintained for at least
several decades when stored under optimal conditions, i.e. at 18ºC with a moisture content of 5 to 9%
(Stein and Owston 2002).
B. Mating system and gene flow
Douglas-fir has a predominantly outcrossing mating system, with selfing rates generally well below
10% in natural populations, selectively harvested stands, and seed orchards (Neale and Adams 1985; Prat
and Arnal 1994; Prat 1995; Prat and Caquelard 1995; Burczyk and Prat 1997; Slavov et al. 2005). Some
trees may have considerably higher selfing rates than average (Stoehr et al. 1998).
Seed orchard studies of mating system and pollen contamination from outside stands indicate that
two-thirds to half of the pollen received by a mother tree originates from nearby pollen parents, and a third
to half comes from more remote sources, either within or outside of the orchard (Burczyk and Prat 1997;
Slavov et al. 2005). Contamination of orchard seedlots with non-orchard pollen can be as high as 60%
within the coastal Douglas-fir range (Adams et al. 1997). This contamination can result in decreased
genetic gain or increased maladaptation, depending on the location and genetic makeup of the seed orchard
(Stoehr et al. 1994).
Based on genetic markers, long-distance gene flow appears to be very low between the coastal and
interior varieties, and between the northern and southern subgroups of the interior variety (Li and Adams
1989; Mitton 1992; Aagaard et al. 1995, 1998a, 1998b; Klumpp 1999; Nelson et al. 2003). However, the
lack of strong differentiation of populations within the coastal variety (St. Clair et al. 2005), and within the
northern subgroup of the interior variety, is indicative of higher levels of gene flow within each of these
two relatively non-fragmented regions (Li and Adams 1989). Populations within the southern subgroup are
much more isolated (Figure 1), although for example during the last glacial period there was considerably
less fragmentation in the Colorado Plateau area and Rocky Mountains (Jackson et al. 2005).
C. Seed production
An old-growth Douglas-fir population may produce 20 to 30 times more cones per hectare than a 50to 100-year-old second-growth stand. Seed crops occur at irregular intervals — on average, one heavy
(mast) crop and one medium crop every 7 years (Owston and Stein 1974; Stein and Owston 2002). Even
during heavy seed years, only about 25% of the trees produce an appreciable number of cones (Isaac
1943). Data on seed fall density in an area will vary widely, but most years less than 2.2 kg fall per ha, of
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which no more than 40% is viable. Years with small seed crops generally have a lower percentage of sound
seeds than mast years, perhaps because the low density of seed and pollen-producing trees results in a
higher level of self-pollination (Garman 1955).
Seed quality also varies during the annual seedfall period. It is higher in the fall of the year but
declines rapidly during winter and spring. This pattern probably results from cone scales in the centre of
the cone — where the highest quality seed are borne — opening early, and scales at the tip and base, which
bear generally poor quality seeds, opening late (Hermann and Lavender 1990).
Both cones and seeds vary greatly in size with latitude and similarly in both varieties, generally with
larger seeds to the south: for example, from coastal Douglas-fir trees, 112,000 cleaned seeds per kg in
British Columbia, 70,000 per kg in California; from interior Douglas-fir trees, 110,000 seeds per kg in
British Columbia, 71,000 per kg in Arizona (Stein and Owston 2002). Seeds of the coastal variety tend to
be larger farther inland than near the coast, and seeds of the interior variety larger than in the coastal
variety (e.g. 115,000 seeds per kg in western Washington, 88,000 per kg in Montana). Also, seeds
sometimes are larger at higher elevations (Stein and Owston 2002). Individual cones can contain up to
52(-63) seeds, but an average of 15 to 20 seeds per cone is more typical in natural populations (Silen 1978;
Vargas-Hernández et al. 2004). Seed size is determined before fertilisation, so there is no correlation
between seed weight and paternity, although seedlings germinating from heavier seeds may be slightly
larger during the first few months of growth (Hermann and Lavender 1990).
Predation of seed by insects, mammals and birds is a major factor limiting natural regeneration.
Competing plant species and unfavourable abiotic environments also reduce success of regeneration.
Although fully stocked stands have been reported 1 to 2 km away from a seed source, the vast majority of
seeds fall within 100 m of seed parent trees (Allen 1942; Dobbs et al. 1974; Barnhart et al. 1996;
Thompson and Schorn 1998; Brocano et al. 2005; Kennedy and Diaz 2005).
Most seed for artificial regeneration of coastal Douglas-fir now originates from seed orchards. Seed
orchard managers promote the differentiation of reproductive buds through applications of synthetic
giberellins (particularly giberellic acids GA4 and GA7), nitrate fertilisation, and partial girdling of stems in
early spring (Silen 1978). Selected parents are grafted into seed orchards; graft incompatibility was a major
problem until genetically high compatibility lines of rootstock were developed (Copes 1999). Cooling of
orchards to delay heat sum accumulation and reproductive bud break is a common method for reducing
pollen contamination in some orchards.
D. Natural regeneration
Douglas-fir seed germinate epigeally from mid-March to early April in the warmer regions of the
range, and as late as mid-May in the cooler areas. Seedling growth during the first year is indeterminate,
relatively slow, and moisture limited. Low moisture availability or a photoperiodic cue can trigger
formation of buds and initiation of bud dormancy by mid-summer. Buds remain dormant until a
genetically-determined chilling requirement is met sometime in winter, and growth resumes in April or
May of the following year (Lavender 1984).
Seedlings of coastal Douglas-fir, particularly in wetter and cooler climates, survive best in high light
when the seed germinates on moist mineral soil or thin burnt-over forest floor. In contrast, seedlings of
interior Douglas-fir, particularly in drier and warmer climates, establish and survive in low light only on a
relatively thick forest floor substrate (Isaac 1943; Schmidt 1957, 1969; Carter and Klinka 1992a). The
establishment of seedlings is enhanced by ectomycorrhizal fungi (Horton et al. 1999; Cline et al. 2005).
First-year seedlings on fresh sites may develop shoots 6 to 9 cm long. Growth in subsequent years is
largely determinate, although some free growth and lammas growth occur in early years. Primary growth
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gradually accelerates so that when saplings are 8 to 10 years old, growth of the terminal leader may
consistently exceed 1 m per yr on highly productive sites (Hermann and Lavender 1990). Lammas shoots
of seedlings and saplings sometimes result in form defects such as forking and ramicorn branching, but
these deviations are confined to wet climates with heavy late-summer rainfall (Carter and Klinka 1986;
Carter et al. 1986; Hermann and Lavender 1990).
First-year germinants have higher survival and growth under light shade, especially on southerly
exposures, but older seedlings require full sunlight, particularly on fresh and moist sites, where Douglas-fir
has low shade tolerance (Carter and Klinka 1992a). Competing vegetation decreases light levels and limits
Douglas-fir regeneration. On water-deficient sites, graminoids and shrubs also compete strongly with
Douglas-fir seedlings for available moisture. Leaves and other organic debris from Pteridium aquilinum
(northern bracken fern) and Chamerion angustifolium (narrow-leaf fireweed) can smother small seedlings.
Regeneration may be more reliable after fire, which can destroy the seed bank of potential competing
species, while forest harvesting can leave areas suitable for the establishment and growth of herbaceous
and woody competitors (Burns 1983; Hermann and Lavender 1990).
Historically, large burned areas (including post-harvest burns) within the range of coastal Douglas-fir
have naturally regenerated to nearly pure stands of Douglas-fir. On fresh sites, where Douglas-fir is
considered an early seral and shade-intolerant species, this process occurred over a relatively short period,
whereas on water-deficient and moist sites, regeneration has required more than 50 years. Regeneration on
water-deficient sites in warmer and drier climates, where Douglas-fir is moderately shade-tolerant and
considered a climax species, occurs under the forest canopy; in fact, temporary protection from the openarea climate is necessary for successful establishment (Daubenmire 1943; Krajina 1965; Ryker 1975;
Hermann and Lavender 1990; Klinka et al. 1990).
From 1950 to 1970, large areas of cutover and burnt forest land in the Pacific Northwest were aerially
seeded for reforestation. With the increase in forest nursery capacity and the ability to better control the
success and density of regeneration through planting, direct seeding became rare (Schubert and Adams
1971; Cleary et al. 1978). One major problem with direct seeding is high seed predation by rodents and
birds, although this problem can be reduced by seeding Douglas-fir seed mixed with a larger amount of
desirable food such as sunflower seeds or oats (Sullivan and Sullivan 1984). Taking into account the range
of sites on which Douglas-fir may grow and its variation in shade tolerance, it can be maintained using a
wide variety of silvicultural systems — including clearcutting, seed-tree, shelterwood and selection
systems. Although success of natural regeneration may be high, the advantage of planting is the
opportunity for much greater initial stocking control and genetic improvement, particularly on productive
sites. An adequate seed source, appropriate seedbed, and suitable microsite are all necessary for successful
natural regeneration.
E. Vegetative reproduction
Douglas-fir does not reproduce vegetatively in nature. Reliable rooting of cuttings is limited to
material collected from trees less than 10 years old, or from trees that have been subjected to repeated
hedging which produces material with a juvenile habit. A second major impediment to the use of cuttings
is that much of this material can have a lengthy period of plagiotropic growth before an erect habit is
assumed (Hermann and Lavender 1990; Ritchie et al. 1994, 1997; Fennessy et al. 2000). Plagiotropic
rooted cuttings become orthotropic more readily when grown outdoors than when maintained in a
greenhouse; the reasons for this are not clear (Ritchie et al. 1997). Both rooted cuttings and plants
produced through tissue culture of cotyledons appear more physiologically mature than seedlings of the
same size (Ritchie et al. 1994). The rooting of stem cuttings is promoted through application of auxins,
either IBA (24.6 mM) or NAA (2.5-7.4 mM) (Copes and Mandel 2000).
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Methods for cloning Douglas-fir genotypes through somatic embryogenesis have been developed and
are entering operational phases (Gadgil et al. 1998; Taber et al. 1998; Zhang et al. 1999; Benowicz et al.
2002). These methods allow for the development of clonal forestry programs, providing the technology to
capture non-additive genetic variation, the opportunity to deploy clonal blocks for specific end uses, and a
regeneration system for propagating genetically transformed material.
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SECTION IV. GENETICS
A. Cytology
The 2C nuclear DNA content of Pseudotsuga menziesii is 38.10 picograms (O’Brien et al. 1996). The
cell nuclear volumes are greater in northern provenances than southern provenances, and in the coastal
variety than the interior variety (El-Lakeny and Sziklai 1971). Unlike all other species of the Pinaceae, the
haploid number of chromosomes in Douglas-fir is 13. Whereas 5 metacentric and 6 submetacentric
chromosomes appear karyotypically similar to those of other studied Pseudotsuga species, Douglas-fir has
2 telocentric chromosomes instead of a sixth large metacentric chromosome as in the other Pseudotsuga
species. Moreover, the chromomycin A3-banding pattern of Douglas-fir chromosomes is different from the
quite similar banding patterns of the two Asian species (Hizume and Kondo 1992). Experimentally,
polyploid Douglas-fir seedlings have been produced (using colchicine) but they were slow-growing and
short-lived (Silen 1978).
In Douglas-fir, as in other species of the Pinaceae, inheritance of chloroplasts is predominantly
paternal (Neale et al. 1986). In contrast, mitochondrial inheritance is maternal (Marshall and Neale 1992;
Aagaard et al. 1998a).
B. Genetic variation
B.1 Population-level variability
Douglas-fir has substantial among-population variation both for quantitative traits and genetic
markers. Population differentiation for quantitative traits related to adaptation to climate can be
considerably stronger than that observed for selectively neutral genetic markers. For example, seedling
studies including samples from a wide range of source environments have found that 13 to 20% of the total
genetic variation for timing of bud set, 11 to 13% of the variation in timing of bud flush, and 47% of the
variation for cold hardiness are attributable to differences among populations within varieties, which is
higher than the average population differentiation for genetic markers (FST) (Table 1) (Howe et al. 2003).
Short-term seedling genecological nursery studies have found significant differentiation of populations,
particularly for bud phenology traits, over distances of only a few km or 100 m of elevation (Rehfeldt
1974, 1979a, 1979b; Campbell 1979, 1986). This variation is associated primarily with temperature of
source environments, and generally reflects a tradeoff between growth rate and cold hardiness, which are
negatively correlated among populations. The importance of this variation at local scales to the health and
productivity of operational plantations has been a subject of debate in practice and the literature. Longterm field provenance trials within the native range and elsewhere have generally failed to show the finegrained geographic patterns of variation observed in detailed seedling genecological trials (White and
Ching 1985), fuelling a debate over the need to manage Douglas-fir genetic resources on a local scale
(Stonecypher et al. 1996; Johnson 1997).
Field provenance trials have shown weaker geographic patterns than seedling studies. In a synthesis of
the results from fifteen (mostly European) countries that established provenance trials from 1967 IUFRO
seed collections, Breidenstein and collaborators (1990) identified four groups of provenance sites based on
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ENV/JM/MONO(2008)30
principal components analysis of climatic data: (1) sites in northeastern Europe with continental climates;
(2) sites in northwestern British Columbia and Norway, along with a few locations in France and Spain,
with cold maritime climates; (3) sites in southwestern British Columbia and northwestern Europe with
moderate maritime climates; and (4) sites in southern Europe with warm maritime climates. Mortality was
higher on sites in groups 1 and 2, and lower on sites in groups 3 and 4. There was substantial provenance
variation in mortality among site groups, with trees from southern coastal Oregon suffering the highest
mortality rates on the coldest (group 1) sites, and provenances from the interior of British Columbia having
the highest mortality on the mildest (group 4) sites (Breidenstein et al. 1990). However, surviving trees
from low-elevation coastal and Cascade provenances in Washington State (USA) were surprisingly
consistent in having the most rapid growth over most sites, showing broad adaptability, although mortality
was high on some colder sites (Kleinschmit and Bastien 1992). Growth generally decreased with
increasing source elevation of provenances. Some northern Oregon provenances from west of the Cascades
as well as a few southwestern British Columbia sources also had high productivity across much of Europe.
Only in continental climates, e.g. in Sweden, Finland and the Czech Republic, did P. menziesii var. glauca
provenances outperform P. menziesii var. menziesii. However, marked changes in provenance performance
between the ages of 17 and 60 in one of the oldest provenance trials, likely due to cumulative effects of
small injuries as well as extreme climatic effects, caution against over-reliance on early field results (Silen
1978).
Although marker-based studies find less among-population variation than provenance and
genecological studies, they confirm that Douglas-fir populations are relatively highly differentiated
compared to various other tree species. A comprehensive rangewide survey of allozyme variation found
that coastal and interior varieties were clearly differentiated, with an average Nei’s genetic distance of
0.083, as were the interior variety’s populations in northern and southern regions, separated by an average
genetic distance of 0.034 (Li and Adams 1989). GST averaged 0.23 between varieties, 0.07 among
populations within the coastal variety, 0.04 for the northern region of the interior variety, and 0.12 for the
southern region of the interior variety (Table 1). These corresponded to average Nei’s genetic distances
among populations of respectively 0.015, 0.008, and 0.012. One of two Mexican populations was clearly
distinct from all the other populations sampled. The strong differentiation of the coastal and interior
varieties has been confirmed with nuclear RAPD (randomly amplified polymorphic DNA) markers.
Mitochondrial RAPD markers exhibited even higher levels of racial and population differentiation
(Aagaard et al. 1995, 1998a, 1998b), and restriction digestion of a region of chloroplast DNA also has
shown strong racial differentiation (Nelson et al. 2003). Chloroplast restriction fragment length
polymorphisms (cpRFLPs) revealed less population differentiation (Ponoy et al. 1994). Chloroplast simple
sequence repeats (cpSSRs) exhibited no differentiation among coastal British Columbia populations,
presumably due to the recent migration into the region after glacial retreat and the long-distance gene flow
via pollen within the region (Viard et al. 2001; Nelson et al. 2003).
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ENV/JM/MONO(2008)30
Table 1. Genetic diversity and population differentiation estimates for Douglas-fir
Marker type, and
Population sampled
Expected
heterozygosity (He)
within populations
Population
differentiation
within races (GST)
0.164
0.07
0.150
0.077
0.04
0.12
0.26
0.05
0.25
0.15
0.07
0.25
0.01
0.04
0.04
0.03
0.75
0.84
Population
differentiation between
races (GST)
Reference
Allozymes
Rangewide n=104
var. menziesii n=43
var. glauca:
northern subgroup n=36
southern subgroup n=24
0.23
Li and Adams 1989
RAPD nuclear markers
Rangewide n=6
var. menziesii n=2
var. glauca:
northern subgroup n=2
southern subgroup n=2
0.25
Aagaard et al.
1998a
RAPD mitochondrial markers
Rangewide n=6
var. menziesii n=2
var. glauca:
northern subgroup n=2
southern subgroup n=2
0.72
Aagaard et al.
1998b
B.2 Variation among individuals within populations
Levels of within-population variation are also high. The average expected heterozygosity (He) based
on allozymes is high for coastal Douglas-fir (0.16) and the northern subgroup of interior Douglas-fir
(0.15), but is half that for the more isolated southern interior subgroup (Li and Adams 1989) (Table 1). In
contrast, for chloroplast DNA markers, levels of within-population variation are higher for interior
populations than coastal populations (Ponoy et al. 1994). Mitochondrial RAPD markers revealed relatively
low levels of within-population variation compared to nuclear RAPD markers, for which within-population
variation was similar to allozymes (Aagaard et al. 1998b). The proportion of total genetic variation due to
within-population variation is considerably higher for presumably selectively neutral molecular markers
than for adaptive traits such as bud phenology (as predicted by theory) (Howe et al. 2003).
The amount of genetic variation and the degree of genetic control of polygenic traits of economic or
adaptive interest within populations of Douglas-fir have been studied extensively (Table 2). Generally,
growth traits and fall cold hardiness are under relatively weak genetic control (individual heritability hi2
<0.3) whereas bud phenology, spring cold hardiness, wood density and graft incompatibility are under
relatively strong genetic control (hi2 ≥ 0.5). The polygenic control of bud phenology and cold hardiness
traits has been verified through quantitative trait loci (QTL) mapping in a three-generation pedigree, with
11 QTL for fall cold hardiness, 15 for spring cold hardiness, and 33 for the timing of bud flush (Jermstad et
al. 2001a, 2001b).
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ENV/JM/MONO(2008)30
2
Table 2. Examples of individual heritability (hi ) estimates for quantitative traits in Douglas-fir
hi2 estimate,
Trait
Variety
Height 1 year
Height 2 years
Height 4 years
menziesii
menziesii
menziesii
0.60
0.46
0.26
Height 12 years
menziesii
0.15 (0.12-0.17)
DBH 12 years
Stem volume 12 years
Lammas growth
occurrence
Lammas growth
occurrence
menziesii
menziesii
0.08
0.08
Christophe and Birot 1979
Christophe and Birot 1979
Christophe and Birot 1979
Adams and Joyce 1990; Stonecypher et al.
1996
Adams and Joyce 1990
Adams and Joyce 1990
menziesii
0.45
Aitken and Adams 1995a
glauca
0.32
Rehfeldt 1983
Date of bud break
menziesii
0.87 (0.45-1.0)
Date of bud break
glauca
0.52
Date of bud set
menziesii
0.70 (0.15-0.81)
Date of bud set
glauca
0.25
Fall cold hardiness
menziesii
0.29 (0.21-0.37)
Winter cold hardiness
Spring cold hardiness
Cambial growth initiation
Cambial growth cessation
Overall wood density
Earlywood density
Latewood density
Latewood proportion
Intra-ring density variation
Graft incompatibility
menziesii
menziesii
menziesii
menziesii
menziesii
menziesii
menziesii
menziesii
menziesii
menziesii
0.11 (0.0-0.35)
0.62 (0.36-1.0)
0.23
0.11
0.59
0.47
0.36
0.24
0.25
0.81
mean or range
Reference
Christophe and Birot 1979; Li and Adams
1993; El-Kassaby and Park 1993; Aitken
and Adams 1995a
Rehfeldt 1983
Li and Adams 1993; Aitken and Adams
1995a, 1995b
Rehfeldt 1983
Aitken and Adams 1996; Aitken et al. 1996;
O’Neill et al. 2001
Aitken and Adams 1995b
Aitken and Adams 1997; O’Neill et al. 2001
Li and Adams 1994
Li and Adams 1994
Vargas-Hernandez and Adams 1991
Vargas-Hernandez and Adams 1991
Vargas-Hernandez and Adams 1991
Vargas-Hernandez and Adams 1991
Vargas-Hernandez and Adams 1991
Copes 1973
C. Inbreeeding depression and genetic load
Douglas-fir has a very high genetic load, with an estimated 10 lethal equivalents per genome
(Sorensen 1969). Controlled outcrossing results in an average of 40 seeds per cone, whereas matings
between half-sibs (inbreeding coefficient F=0.125) produce 31 seeds per cone, full-sib and parent-offspring
matings (F=0.25) produce 23 seeds per cone, and self-pollination (F=0.50) averages just over one seed per
cone (Sorensen and Cress 1994). Growth of seedlings and young trees is reduced by about 7% for every
0.1 increase in F (Sorensen 1997).
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SECTION V. HYBRIDISATION
Experimental hybrids between Pseudotsuga menziesii and P. macrocarpa have been reported (Ching
1959; Gause 1966; Orr-Ewing 1966a, 1966b). The present natural ranges of these species do not overlap,
being about 35 km apart. Attempts to hybridise P. menziesii with generally accepted Asian species of the
genus have failed, producing only empty seeds (Orr-Ewing 1966a, 1966b, 1971; Silen 1978). This failure
is likely because of the different number of chromosomes in P. menziesii (2n = 26) from the diploid 2n =
24 present in other species of the genus, but does not explain the interspecific crossing success with
P. macrocarpa (Silen 1978). Attempts to hybridise P. macrocarpa with P. japonica and P. sinensis also
have failed, producing only empty seeds (Orr-Ewing 1975).
Experimental crosses made in British Columbia of Pseudotsuga flahaultii (from western Chihuahua,
Mexico) with P. menziesii var. glauca and P. menziesii var. menziesii (Orr-Ewing et al. 1972) were
successful. The two generally accepted Douglas-fir taxa P. menziesii var. menziesii and P. menziesii var.
glauca are completely interfertile experimentally. Intervarietal hybrids and F2 crosses of such hybrids
combine high growth rates with good frost resistance, and have been used in breeding programs in
Germany (Braun 1992, 1999). Natural introgression of these two varieties may take place where their
present ranges meet, for example in the interior of British Columbia (von Rudloff 1972; Li and Adams
1989), but in other areas of proximity the populations may remain distinct, possibly because of their local
adaptation (e.g. St. Clair et al. 2005). When British Columbia was covered by the Cordilleran ice sheet
18,000 years ago, the varieties were isolated from each other farther to the south as coastal and Rocky
Mountain populations; their convergence in interior British Columbia may have taken place no earlier than
7000 years ago (Tsukada 1982; Bartlein et al. 1998).
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SECTION VI. ECOLOGY
This section focuses on the ecological information from Canada and the United States.
A. Autecology
Douglas-fir has an extensive geographical and elevational range, with the broadest ecological
amplitude of all the western North American tree species. It grows in a wide variety of climates (arranged
here in order of increasing frequency of presence): subalpine boreal, boreal, semiarid, temperate, and
mesothermal (Hermann and Lavender 1990; Klinka et al. 2000). The Pacific region has a maritime climate
with cool, relatively dry summers and wet, mild winters, with a long frost-free period and relatively narrow
diurnal temperature fluctuations (6 to 8ºC). Precipitation falls mostly as rain, and is concentrated in the
winter. The interior, Cordilleran region has a continental climate. In the northern part of the range of
interior Douglas-fir, frost can occur in any month of the year. Precipitation in the northern Rocky
Mountains is relatively evenly distributed throughout the year, with the exception of a dry period during
July and August. In the central Rocky Mountains, summers are hot and very dry in some areas, and winters
are long and severe. The southern Rocky Mountains east of the Continental Divide generally have high
rainfall during the growing season but low winter precipitation; west of the Continental Divide, the rainfall
is bimodal, being more evenly divided between winter and summer. In the Sierra Madre Occidental of
northern Mexico, the precipitation is primarily in the summer months, with occasional winter rainfall (but
sometimes severe drought), average low temperature in January below freezing at higher elevations, and a
spring dry period (Fulé and Covington 1999; Cleaveland et al. 2003; González-Elizondo et al. 2005).
Within these large regions the climate also varies considerably, which is readily notable with
elevation. In general, temperature decreases and precipitation increases with increasing elevation
throughout the Coastal ranges, Sierra Nevada, and Rocky Mountains. At middle and high elevations
particularly north of Mexico, the winters are colder, the frost-free season is shorter, diurnal temperature
fluctuations are larger (10 to 16ºC), and much of the precipitation falls as snow.
Douglas-fir grows across nearly the entire range of conditions of soil moisture (very dry to very
moist) and soil nutrients (very poor to very rich), but the most productive growth occurs on fresh to moist,
nitrogen-rich soils. Douglas-fir has a greater tolerance of water- and nutrient-deficient soils than many
other native tree species (Krajina 1969; Klinka et al. 2000).
Site index is an expression of site productivity, based on the height of dominant or codominant trees
at a standard base age (usually 50 years). Relationships between potential site index of the coastal variety
and analytical and categorical measures of site quality have been quantified in the Coastal Western
Hemlock zone of British Columbia (Klinka and Carter 1990). Site index increased with increasing soil
water supply, peaked between fresh and moist sites, and then decreased with increasing water surplus. Site
index also increased with increasing nitrogen availability, even on water-deficient sites (Figure 2). All the
trends in site index – site quality relationships are supported by regression analysis indicating that each soil
moisture and soil nutrient regime had a strong relationship with site index. The best quantitative soil
measures related to site index were water deficit and mineralisable nitrogen in the first 30 cm of mineral
soil, which together accounted for 63% of the Douglas-fir site index variability.
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ENV/JM/MONO(2008)30
Both soil moisture and soil nitrogen are major determinants of Douglas-fir growth in the Coastal
Western Hemlock zone (British Columbia) and likely in other environments (Carter and Klinka 1992b).
Douglas-fir will respond to nitrogen fertilisation, with the magnitude of response decreasing with
increasing soil water surplus and the available nitrogen (Carter et al. 1998) (Figure 3).
Figure 2. Douglas-fir site index relative to soil moisture and soil nutrient regimes in a dry, cool
mesothermal climate of coastal British Columbia, Canada
Relationships between soil nutrient regimes and several empirical variables (site n=149).
Different superscripts within rows indicate significant differences among the soil nutrient
regimes (p<0.05, Tukey's test) (from Carter and Klinka 1990)
Coastal Douglas-fir reaches its best growth on well-aerated, deep soils with a pH from 5 to 6. In
coastal northern California, Oregon and Washington, soils originated chiefly from marine sandstone and
shales with scattered igneous intrusions. Surface soils are generally acidic, low in base saturation, and high
in organic matter and total nitrogen. Soils supporting coastal Douglas-fir have textures ranging from
gravelly sands to clays. Soil depth varies from very shallow on steep slopes and ridgetops, to deep where
there are deposits of volcanic origin as well as residual and colluvial materials. Soil orders characteristic of
the range of coastal Douglas-fir include Ultisols, Inceptisols, Spodosols and Entisols (Heilman et al. 1979).
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ENV/JM/MONO(2008)30
Figure 3. Edatopic grid showing pre-treatment foliar nitrogen (N, %) and sulphate-sulphur (SO4-S, ppm), and
isolines of relative basal-area response, indicating 3rd-year response of Douglas-fir to nitrogen fertilisation
Dashed isolines are extrapolations. Soil nutrient regimes (detailed in Figure 2) are: VD=very dry,
MD=moderately dry, SD=slightly dry, F=fresh, M=moist, and VM=very moist. Encircled numbers
are site units: 1=Cladonia spp., 2=Gaultheria shallon, 3=Rhytidiadelphus loreus, 4=Blechnum
spicant, 5=Tiarella trifoliata, and 6=Athyrium filix-femina (from Carter and Klinka 1992b)
Soils in the range of interior Douglas-fir originated from an array of parent materials ranging from
basaltic talus and deep loess with volcanic ash to thin residual soil over sedimentary or granitic rocks. The
soils are mostly Alfisols, Inceptisols, Mollisols, Spodosols and Entisols. Limestone comprises a significant
portion of the sedimentary rock, and gives rise to neutral or alkaline soils ranging in texture from gravelly
silts to gravelly loams (Alexander 1974; Pfister et al. 1977).
The elevational distributions of both coastal and interior Douglas-fir decrease from south to north,
reflecting the effect of latitude on temperature. Principal limiting factors are low temperature in the
northern, high temperature in the far southern portions of the range, and low moisture especially in the
southern portion (e.g. Adams and Kolb 2005; Case and Peterson 2005). Interior Douglas-fir generally
grows at considerably higher elevations than coastal Douglas-fir at comparable latitudes. The highest
elevation where interior Douglas-fir grows north of Mexico is 3260 m, on the crest of Mount Graham in
southeastern Arizona (Hermann and Lavender 1990). Populations in Mexico generally occur between
2000-3600 m, on northern exposures (Acevedo-Rodríguez et al. 2006).
In summary, Douglas-fir tolerates water- and nutrient-deficient soils but not water-surplus and
flooded soils (Krajina 1969; Klinka et al. 2000). In the Pacific Northwest and Intermountain Northwest,
nitrogen is the only nutrient in forest soils that has been shown to limit the growth of Douglas-fir (Miller et
al. 1986; Moore 1988).
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Juvenile life-history characteristics are described above in Section III, Subsection D (Natural
regeneration). Coastal Douglas-fir can reach reproductive maturity at 7 to 10 years of age, whereas Rocky
Mountain Douglas-fir is slower to reproduce (Stein and Owston 2002). Sapling-age trees produce
relatively few cones, investing most energy in rapid height growth under competition for light. Maximum
fecundity occurs between 100 and 200 years, but younger trees produce fewer, larger cones and more
viable seeds per cone (Stein and Owston 2002). The species produces relatively fewer cones in most years
but large crops at intervals of 2 to 7 years (Owens 1973).
Coastal Douglas-firs commonly reach maximum heights of 76 m and diameters (dbh) of 150-180 cm.
Among the living trees, one of the largest on record (1998) reached 85.6 m in height and 408 cm dbh, with
a crown spread of 22 m, and wood volume of 308 m3 (AFA 2000). The most massive recorded tree (1998)
had a wood volume of 349 m3 (height 73.8 m, dbh 423 cm, crown spread 23 m); and the tallest living tree
(1998) reached 99.4 m (dbh 354 cm) (Van Pelt 2001). Historically, purportedly larger trees were reported,
with heights of 115-127 m. Douglas-fir thus remains among the world’s few tallest species. The lifespan of
coastal Douglas-fir typically reaches some 500 years, with the oldest known tree attaining about 1350
years (McArdle et al. 1961; Hermann and Lavender 1990). Rocky Mountain Douglas-firs are smaller,
averaging 30-37 m in height and 38-102 cm dbh, with one of the most massive recorded being 42.4 m in
height and 255 cm dbh, and the tallest reaching 67.4 m with 179 cm dbh. The interior variety typically
lives to around 400 years, although relatively frequent fires often kill trees at a younger age (Hermann and
Lavender 1990); they can attain a known lifespan of some 1275 years. The Douglas-fir generations in an
area can be overlapping or discrete, and long or short, depending on the agents of disturbance and whether
the stands were even-aged or uneven in age.
B. Synecology
Depending on site and disturbance history, Douglas-fir can grow in even- or uneven-aged stands and
in monospecific or mixed-species stands. It may be present in all seral stages of secondary succession, and
can form old-growth stands on some sites.
As a result of its wide climatic amplitude, Douglas-fir is a minor or major component in many
regional ecosystems (climatic or vegetation zones): for example, in British Columbia it occurs in 10 of the
12 forested zones. It is the major late seral species in the Interior Douglas-fir zone and Coastal Douglas-fir
zone (Krajina 1965, 1969; Meidinger and Pojar 1991; Klinka et al. 2000). Given its relatively wide edaphic
amplitude, Douglas-fir can be a minor or major, temporary or self-perpetuating component of local
ecosystems (plant associations, site types, habitat types, or forest cover types), but it is absent on wet sites,
sites with a strongly fluctuating water table, and sites affected by ocean spray (Krajina 1969; Klinka et al.
2000).
The major associates of coastal Douglas-fir may include Abies amabilis (Pacific silver fir), A. grandis
(grand fir), A. concolor (white fir), Acer macrophyllum (bigleaf maple), Alnus rubra (red alder), Arbutus
menziesii (Pacific madrone), Chamaecyparis lawsoniana (Port Orford-cedar), Libocedrus decurrens
(incense-cedar), Picea sitchensis (Sitka spruce), Pinus monticola (western white pine), Quercus
chrysolepis (canyon live oak), Q. garryana (Garry oak), Q. kelloggii (California black oak), Q wislizeni
(interior live oak), Sequoia sempervirens (coast redwood), Thuja plicata (western redcedar) and Tsuga
heterophylla (western hemlock). Those species above that also occur in the Cordilleran region are also
associated with interior Douglas-fir. Its other major associates are Abies lasiocarpa (subalpine fir), Larix
occidentalis (western larch), Picea glauca (white spruce), Pinus contorta (lodgepole pine), P. ponderosa
(ponderosa pine) and Populus tremuloides (trembling aspen) (Franklin and Dyrness 1973; Eyre 1980;
Hermann and Lavender 1990).
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ENV/JM/MONO(2008)30
Coastal Douglas-fir is a major component of four forest cover types (Eyre 1980): Pacific Douglas-fir
(229), Douglas-fir−Western Hemlock (230), Port Orford Cedar (231) and Pacific Ponderosa
Pine−Douglas-fir (244). It is a minor component of the following ten cover types: Red Alder (221), Sitka
Spruce (223), Western Hemlock (224), Western Hemlock−Sitka Spruce (225), Coastal True Fir−Hemlock
(226), Western Redcedar−Western Hemlock (227), Western Redcedar (228), Redwood (232), Oregon
White Oak (233) and Douglas-fir−Tanoak−Pacific Madrone (234).
Interior Douglas-fir is a principal species in three forest cover types (Eyre 1980): Interior Douglas-fir
(210), Western Larch (212) and Grand Fir (213). It is a minor component in five cover types: Engelmann
Spruce−Subalpine Fir (206), White Fir (211), Western White Pine (215), Aspen (217) and Lodgepole Pine
(218).
The cover and composition of understory vegetation within forest cover types vary depending on site
(climate and soil), associated tree species, stand developmental stage, and stand density. Relative to other
tree species, light interception by the canopy of Douglas-fir is intermediate, thus providing light conditions
for the development of diverse understory vegetation.
Plantations of Douglas-fir in Europe, Argentina, Chile and New Zealand have been sources of natural
reproduction for the naturalisation of Douglas-fir (MacLaren 1996; Knoerzer 1999; Ledgard and Langer
1999; Simberloff et al. 2003; Brocano et al. 2005). The rapid growth that has made Douglas-fir an exotic
species of economic value with plantations in many areas may, in some cases, result in ecological
problems as it can out-compete native species and potentially become invasive. There is some concern that
conversion of native hardwood or grassland ecosystems to Douglas-fir dominated forests may result in
changes in species composition, including insect communities, and soil acidity, fertility or nitrification
(Alfredsson et al. 1998; Knoerzer 1999; Knoerzer and Reif 2001; Gossner and Simon 2002).
C. Stand dynamics
Periodic recurrence of major wildfire events has sometimes created large, rather pure stands of
Douglas-fir, more so in the Pacific region than the Cordilleran region (e.g. Winter et al. 2002a, 2002b;
Briles et al. 2005; Brunelle et al. 2005). The species’ rapid growth and longevity, with thick corky bark of
lower boles and main roots of older trees (cf. Kuiper and Coutts 1992; McConnon et al. 2004), and
epicormic branching (Ishii and Ford 2001) are main adaptations that have enabled Douglas-fir to remain a
dominant element in Pacific Northwest forests. Without major fire or other severe disturbance, Douglas-fir
would gradually be replaced throughout much of this range by more shade-tolerant conifers. Although
harvesting has reduced the area of the original old-growth forest, clearcutting with slash burning followed
by natural regeneration and/or planting has helped maintain Douglas-fir as the major component in secondgrowth stands. Where regeneration has been only partially successful or failed, Pinus contorta, broadleaved trees or shade-tolerant conifers have become associates of Douglas-fir or replaced it altogether
(Hermann and Lavender 1990). On the other hand, the historically recent lack of landscape-scale fire in
some other areas of the western United States is causing encroachment of Douglas-fir into grasslands
(Arno and Gruell 1986; Barnhart et al. 1996; Kennedy and Diaz 2005).
In Mexico, Pseudotsuga is a minor component in mixed-pine and Abies forests (e.g. AcevedoRodríguez 1998; Aguirre-Calderón et al. 2003; Domínguez-Álvarez et al. 2004). For example, it occurs in
the Sierra Madre Oriental in Abies vejarii forests, and in Central Mexico with A. religiosa, and it is also
found in association with Pinus ayacahuite and P. hartwegii.
The variation in shade tolerance of Douglas-fir from intolerant to moderately tolerant (Krajina 1965,
1969; Klinka et al. 1990; Carter and Klinka 1992a) is reflected in stand dynamics. In wetter and cooler
climates (predominantly in the Pacific region, except on very dry sites in the rain shadow of the Olympic
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ENV/JM/MONO(2008)30
Mountains and southwestern Oregon and northern California), shade-intolerant Douglas-fir can be a minor
or major but persistent seral species. Over several hundred years in the absence of stand-destroying events,
it is replaced by shade-tolerant Abies amabilis, Thuja plicata and/or Tsuga heterophylla (Franklin and
Dyrness 1973; Hermann and Lavender 1990). In drier and warmer climates (predominantly in the
Cordilleran region, except the interior wet belt), moderately shade-tolerant Douglas-fir is a minor or major
climax species: it is self-perpetuating under its own canopy. It replaces species such as Pinus ponderosa,
P. contorta and Larix occidentalis. However, in the interior wet belt it functions as a minor or major seral
species and is gradually replaced by shade-tolerant Abies grandis, A. lasiocarpa, Picea engelmannii, Thuja
plicata and/or Tsuga heterophylla (Daubenmire 1943; Krajina 1969; Alexander 1988).
D. Damaging agents
Throughout life Douglas-fir is subject to damage from a variety of agents. It is host to hundreds of
fungi, but relatively few cause serious damage. Over sixty species of insects attack Douglas-fir cones, but
only a few result in significant damage to seed crops. Seed and cone insects include Contarinia
oregonensis (Douglas-fir cone gall midge) and C. washingtonensis (Douglas-fir cone scale midge)
(Diptera: Cecidomyiidae); Leptoglossus occidentalis (western conifer seed bug) (Hemiptera: Coreidae);
Megastigmus spermotrophus (Douglas-fir seed chalcid) (Hymenoptera: Torymidae) (von Aderkas et al.
2005b); Eupithecia spermaphaga (fir cone looper) (Lepidoptera: Geometridae); Dioryctria abietivorella,
D. pseudotsugella and D. reniculelloides (coneworms) (Lepidoptera: Pyralidae); Barbara colfaxiana
(Douglas-fir cone moth) (Lepidoptera: Yponomeutidae); and Frankliniella occidentalis (western flower
thrip) (Thysanoptera: Thripidae) (Hedlin et al. 1980). The damage by insects is frequently more
pronounced during the years of light or moderate seed crops that follow mast crops (Furniss and Carolin
1977).
Various species of Pythium and Rhizoctonia (Peronosporales: Pythiaceae) and Phytophthora,
Fusarium and Botrytis (Incertae sedis) fungi may cause significant seedling mortality in nurseries
(Peterson and Smith 1975; Sutherland and van Eerden 1980). The root rots Rhizina undulata (Pezizales:
Rhizinaceae), Armillaria ostoyae (Agaricales: Marasmiaceae) and Phellinus weirii (Hymenochaetales:
Hymenochaetaceae) cause significant damage in plantations. The latter two fungi represent a serious threat
to the management of young stands — trees either die or are weakened and blown over. The only effective
control measures include removing infected stumps and introducing non-host species, and preclude
continuous crop rotations of Douglas-fir. Many heart-rot fungi infect Douglas-fir; of these the most
damaging and widespread is Phellinus pini, but Phaeolus schweinitzii (Polyporales: Polyporaceae) also
causes serious problems. The main entry points for infection are knots and scars caused by fire, lightning
and falling trees. Losses from heart rots far exceed those from any other type of decay (Hermann and
Lavender 1990). Other fungi found predominantly on dead wood of Douglas-fir include Fomitopsis
cajanderi and F. pinicola (Polyporales: Fomitopsidaceae) (Hepting 1971).
Among needle diseases the most conspicuous is needle cast caused by Rhabdocline pseudotsugae
(Heliotiales: Hemiphacidiaceae). It mainly affects younger trees, and typically only causes substantial
damage after prolonged periods of rain while new needles are emerging. Phaeocryptopus gaeumannii
(Pleosporales: Venturiaceae) needle blight is a serious problem in off-site plantations, especially in
southern coastal Oregon. Serious stem deformities in the dry southern interior are caused by the dwarf
mistletoe Arceuthobium douglasii (Santalales: Viscaceae), which occurs throughout most of the range of
Douglas-fir (Hawksworth and Wiens 1996).
On interior Douglas-fir the most damaging instects are Orgyia pseudotsugata (Douglas-fir tussock
moth) (Lepidoptera: Lymantriidae) and Choristoneura fumiferana (western spruce budworm)
(Lepidoptera: Tortricidae). Both of these insects can attack trees of all ages at recurrent intervals (e.g.
Campbell et al. 2005), and often result in severe defoliation. Dendroctonus pseudotsugae (Coleoptera:
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Scolytidae) is a destructive bark beetle in old-growth stands of both coastal and interior Douglas-fir, but its
impact is declining with the conversion to second-growth management and rotations of less than 100 years
(Furniss and Carolin 1977).
Consumption of Douglas-fir seeds by small mammals and birds further impacts the quantity of seed
available for regeneration. As most seedfall occurs at least 150 days before the germination period, the
rodent Peromyscus maniculatus (deer mouse), can consume a great majority of the seed on the ground
(Hermann and Lavender 1990). Browsing and clipping of seedlings and saplings by Lepus americanus
(snowshoe hare), L. townsendii (jackrabbit), Aplodontia rufa (mountain beaver) and Thomomys talpoides
(pocket gopher) often cause injury. Odocoileus spp. (deer) and Cervus elaphus (elk or wapiti) can also
injure young trees (Black et al. 1979). In the Cordilleran region, domestic livestock can damage seedlings
considerably through trampling and browsing.
High winds occasionally cause extensive blowdown of coastal Douglas-fir in the Pacific Northwest,
particularly when following heavy rain. Scattered breakage of tree tops in dense, young stands can result
from heavy snow and ice storms. Seedlings are vulnerable to both late spring and early fall frost events
(Timmis et al. 1994). Interior Douglas-fir is less cold hardy than most sympatric conifers. Cold injury can
be a concern with exotic plantations, for example in Europe and New Zealand (Hermann and Lavender
1999). In North America, crown fires can destroy stands of all ages; however, older Douglas-fir trees with
thick bark are resistant to ground fires (Hermann and Lavender 1990).
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SECTION VII. FORESTRY PRACTICES
A. Deployment of reforestation materials
Douglas-fir is one of the most commonly regenerated trees in western North America, with the area
planted now surpassing that regenerated naturally. Douglas-fir is grown in monospecific stands or mixedspecies stands with shade-tolerant or shade-intolerant species. Depending on site and management
objectives, clearcutting, seed-tree, shelterwood, and selection reproduction cuttings are effective
silvicultural systems for its establishment and growth (Burns 1983). Propagation by seed is the primary
method for regenerating the species. An overview of techniques for collection, processing, testing and
storage of seed is in Stein and Owston (2002). Bare-root seedlings are predominantly used for artificial
regeneration in the United States, and containerised seedlings in Canada. Most seed used for reforestation
of coastal Douglas-fir comes from seed orchards. Interior Douglas-fir is largely regenerated by planting
seedlings grown from wild-collected seed or is regenerated naturally, although young seed orchards will be
providing more seed for the northern portion of the range (FGCBC 2001). Detailed information for pollen
management is provided by Webber and Painter (1996).
Pseudotsuga menziesii has been a major component of western North American forests since the midPleistocene (Hermann 1985). The known fossil record indicates that the species’ native range did not
extend beyond western North America, although Pseudotsuga fossils have been found in Alaska, Beringia
and East Asia (Bartlein et al. 1998; Schorn and Thompson 1998). The arrival of David Douglas at Fort
Vancouver (Washington State, USA) in April 1825 to collect seeds and plants for the Horticultural Society
of London marked the beginning of the introduction of many North American species into Europe. He sent
home many seeds and specimens, including Douglas-fir. Of all the North American species introduced into
Europe, none has become more important (Hermann 1987; de Champs 1997). Plantations exist in many
European countries ranging from Portugal to Russia, and Italy to Finland. The countries with the largest
area of Douglas-fir plantations are France, where it is predicted to cover about 500,000 ha by 2010-2020,
and Germany and Great Britain, where stands currently occupy about 80,000 ha and 50,000 ha,
respectively. In the last 100 years Douglas-fir has been successfully introduced into many regions of the
world’s temperate forest zones, where it is grown in forests, arboreta and parks (Hermann 1987; Hermann
and Lavender 1999).
B. Provenance transfer
The early introductions of Douglas-fir to Europe originated from coastal (Pseudotsuga menziesii var.
menziesii) provenances, whereas some later seed imports from more interior regions (likely P. menziesii
var. glauca) produced less successful plantations (Kleinschmit and Bastien 1992). Field provenance trials
were first established in 1912 in Germany (Stimm and Dong 2001), and in 1913 in the Pacific Northwest
(Munger and Morris 1936; Irgens-Möller 1968; Ching and Hermann 1977). Subsequently provenance trials
were established in locations including Europe (Göhre 1958), New Zealand (Sweet 1964), Michigan
(Steiner 1979), California (Griffin and Ching 1977), the Pacific Northwest (Ching and Bever 1960; Ching
1965; Rowe and Ching 1973; White and Ching 1985) and British Columbia (Haddock et al. 1967). The
early literature on provenance variation was compiled by Hermann and Ching (1975). The early trials
generally included relatively few provenances planted on relatively few sites, but still showed strong
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differentiation between the coastal and interior varieties in growth rate, frost hardiness, drought resistance
and resistance to needle cast diseases (including Rhabdocline pseudotsugae and Phaeocryptopus
gaeumannii) (Kleinschmit and Bastien 1992), which indicated the need for controlled seed transfer. Seed
zones and seed transfer guidelines are designed to promote the utilisation of local, well-adapted and
productive seedlots for reforestation by limiting movement of seed from the place of collection to the site
for reforestation. Seed zones usually require that seedlots are collected and used within the same defined
geographic area and elevational range, whereas seed transfer rules limit movement to some maximum
latitudinal, longitudinal and elevational distance. For use as an exotic for reforestation or afforestation,
seed transfer regulations define the area within the native range from which seed can be obtained.
In 1966 the International Union of Forest Research Organizations (IUFRO) initiated a systematic
rangewide collection of 182 provenances of Douglas-fir, with seed distributed to 59 organisations in 36
countries to develop seed transfer rules for Europe (Kleinschmit and Bastien 1992). Provenance trials
established from this collection varied in experimental design, number of provenances, and year planted,
but have generated a wealth of information on optimal seed sources for use as an exotic (e.g. Breidenstein
et al. 1990; Kleinschmit and Bastien 1992; Beran 1995; Kleinschmit et al. 1995; Kranenborg and de Vries
1995; Orlić and Ocvirek 1995; Vega et al. 1995). The results of these trials (summarised in Section IV.
Genetics) have been used to develop seed transfer rules for European countries based on North American
seed zones, to ensure that plantations are established from well-adapted, productive provenances
(Kleinschmit and Bastien 1992). There is also considerable within-provenance variation for breeding
programs to utilise, indicating that productive landraces can be developed from a range of provenances.
Potential seed-collection areas for European forestry were defined following the IUFRO provenance trial
(Fletcher et al. 1981; Fletcher and Bastien 1988, 1989 – cited in Kleinschmit and Bastien 1992). The
emphasis of Douglas-fir programs in western Europe has shifted from provenance selection to breeding
programs using select genotypes from a range of appropriate sources.
Seed zones and seed-transfer guidelines for Douglas-fir within its native range are among the most
conservative for western North American conifers. The guidelines are based in part on the relatively finescale geographic variation observed in seedling genecological trials (Rehfeldt 1974; Campbell 1979;
Rehfeldt 1979a, 1979b; Campbell 1986). Field provenance trials have not shown the degree of local
adaptation or the steepness of genetic clines that these seedling experiments have displayed. It is not clear
if the differences in results between nursery and field trials are due to tree age, test environment, sampling
issues, or experimental design problems (White and Ching 1985).
In coastal Oregon and Washington State, seed zones have recently been expanded slightly (Randall
1996; Randall and Berrang 2002). Douglas-fir still has more seed zones, and narrower elevational bands
within zones (150 to 600 m), than other sympatric conifers in this region. In British Columbia, the seed
planning zones are generally larger than in USA, and they are larger in the coastal region than the interior
region. The maximum permitted distances for seed transfers of wild-stand seedlots of coastal Douglas-fir
for reforestation within seed planning zones in British Columbia are up to 3º latitude to the north, up to 2º
latitude to the south, within long (north to south) and narrow (east to west) seed planning zones, and 350 m
up or down in elevation (BCMF 1995). Comparable maximum transfers for interior Douglas-fir within
seed planning zones are 2º latitude north and 1º south, 3º longitude west and 2º east, and 200 m up in
elevation and 100 m down.
C. Breeding programs
Breeding programs for coastal Douglas-fir are among the oldest and are the largest in the Pacific
Northwest, with large numbers of progeny tests and seed orchards (Adams et al. 1990). Like seed zones,
breeding zones for coastal Douglas-fir are generally long north-south and narrower east-west, reflecting
coastal climatic gradients. The appropriate geographic size of breeding zones for coastal Douglas-fir has
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been controversial, due to the conflicting provenance and genecological test results described above. Some
programs, such as the Pacific Northwest Tree Improvement Cooperative program, started with many small
breeding zones based on the fine-scaled geographic variation observed in provenance trials and seedling
genecological studies (Silen and Wheat 1979), and reinforced by quantification of substantial genotype-byenvironment interaction in progeny trials (Campbell 1992). Other programs have delineated much larger
breeding zones based on a lack of genotype-by-environment interaction in the field growth of highly
ranked families and a lack of correspondence between genotype-by-environment interaction and variation
in physical environments between test sites (Stonecypher et al. 1996; Johnson 1997).
Early breeding programs focused on obtaining genetic gain through intensive phenotypic selection in
wild stands. This resulted in gains of a few percent for juvenile growth (Stonecypher et al. 1996).
Subsequent progeny testing and selection resulted in gains of around 10% for growth rate in the first
generation. Some breeding programs used open-pollinated progeny trials, whereas others had progeny
testing of extensive partial diallel matings. In the latter, the amount of non-additive genetic variation for
traits of interest was found to be about half that of additive genetic variation (Stonecypher et al. 1996),
although this varies greatly among sets of genotypes (Yanchuk 1996). Thus, programs focus primarily on
utilising additive variation. As cloning technology improves (e.g. somatic embryogenesis), interest may
increase in capturing some non-additive variation through deployment of clones in some situations.
The objectives for these selective breeding programs are to increase volume growth while maintaining
quality traits including stem form, wood density and branch diameter. In western Europe, increasing spring
cold hardiness through delaying bud burst is also of interest (e.g,. Heois 1994). Most programs are
currently in the second generation of breeding and testing. Selection for faster growth can lead to a greater
frequency of lammas growth on highly productive sites, and this can produce forking and ramicorn
branching defects (Adams and Bastien 1994; Schermann et al. 1997), so lammas growth is selected against
in some programs. Some breeding lines within multiple-population breeding programs focus on increasing
wood density. Stem volume and wood density are moderately negatively genetically correlated, so
simultaneous improvement of these traits is difficult. Breeding efforts for interior Douglas-fir in British
Columbia, Idaho and Montana are more recent and smaller in scale than their coastal counterparts, but also
focus on increasing wood volume, with wood density as a secondary consideration (FGCBC 2001).
Cooperative European breeding efforts have arisen from the IUFRO provenance trial among France,
Belgium, Spain and Germany, with a base population of 10 provenances and 50 open-pollinated progeny
from each (Kleinschmit and Bastien 1992).
Estimates of the optimum age for genetic selection for increased growth rate have ranged from 4 years
in highly cultivated, intensive farm field tests up to 7 to 18 years in some field trials (Magnussen and
Yanchuk 1994; Woods et al. 1995; Johnson et al. 1998). Seedlings 1 or 2 years of age can be used to
identify the poorest families and cull genotypes prior to establishing progeny trials, but the best families
cannot be identified in early tests (Adams et al. 2001). Final selections have typically been made in field
trials at 12 to 15 years. Spacing of trees or testing genotypes in mixtures versus pure blocks does not
significantly affect estimation of genetic parameters or genotype rankings (St. Clair and Adams 1991;
El-Kassaby and Park 1993).
D. Conservation of genetic resources
The inherently high genetic diversity of Douglas-fir, both within and among populations, is being
conserved both in situ in natural parks, ecological reserves and other protected areas across most of the
species’ range, and ex situ in seed orchards, breeding archives and genetic field tests. Geographic
information system-based spatial analyses of the adequacy of in situ protection of Douglas-fir in parks
have recently been conducted in British Columbia, Washington and Oregon, and its ecological envelope
has also been modelled in relation to protected areas (Coulston and Riitters 2005). In British Columbia,
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in situ protection was analyzed for each of twelve Seed Planning Units (SPUs) used for managing seed
transfer and breeding programs (Hamann et al. 2004). Only protected areas over 250 ha with at least 5000
mature-equivalent individuals were considered adequate reserves. The number of protected areas meeting
these criteria in each SPU ranged from two to sixty. Nearly all of the SPUs appeared to have sufficient
conservation populations, with the Cariboo Transition SPU near the northern edge of the Pseudotsuga
menziesii var. glauca range being the only area judged to need field verification of adequacy of protection.
In Washington and Oregon, the analyses were conducted based on both seed zones and ecoregions.
The conservation threshold set was that at least 5000 reproductively mature individuals be protected in
parks and ecological reserves in each spatial unit (Lipow et al. 2004). Of 204 seed zone-by-elevation bands
in Washington and western Oregon, 198 were well protected. The primary in situ conservation gap was in
the Puget Lowlands of western Washington State (Lipow et al. 2004; Coulston and Riitters 2005), an area
of high forest productivity. Fortunately genotypes from this region are well represented in ex situ
collections (Lipow et al. 2004). Provenances from the region are well represented and important in
breeding populations in western Europe (Kleinshmidt and Bastien 1992). In eastern Oregon, 14 of 18
breeding zone-by-elevation bands were also considered well protected; conservation gaps were identified
in the Fort Rock and Chiloquin breeding zones, but unprotected stands of Douglas-fir in these midsouthern areas were considered unlikely to be harvested. Additional protected areas were considered
desirable for the species in northwestern California (Coulston and Riitters 2005), and greater protection for
populations in Mexico (Vargas-Hernández et al. 2004).
In addition to in situ conservation reserves and extensive ex situ resources in seed banks, provenance
and progeny trials, and breeding populations within the native range, there are considerable ex situ
collections of Douglas-fir in both North America and Europe. In France, Germany and Belgium, over 1000
ha of ex situ gene conservation plantations have been established from provenances of interest in USA
(Kleinschmidt and Bastien 1992). The widespread use of relatively local seed and breeding zones to
control the movement of seed for reforestation within the native range also maintains adaptation and
geographic variation in reforested areas.
Many studies have evaluated genetic diversity of Douglas-fir resulting from forest management
practices, and generally have found little change relative to wild populations. Alternative regeneration
methods have been compared, including shelterwood systems, group selection and clearcutting followed
by natural regeneration or planting (Adams et al. 1998). In general, harvesting and regeneration methods
had little effect on genetic diversity, although harvesting from below (removing smaller trees) in the
shelterwood method resulted in removal of some rare, possibly deleterious alleles. Similarly, the
silvicultural system had little effect on the mating system (Neale and Adams 1985). First-generation and
second-generation domesticated populations of coastal Douglas-fir in British Columbia and Washington
have similar or higher levels of genetic diversity than wild populations, although second-generation
populations differ slightly for some allele frequencies from wild populations (El-Kassaby and Ritland
1996a, 1996b). It has been suggested that slightly higher levels of genetic diversity would be maintained
through nursery production of seedlings if single seeds were sown from bulked seedlots or if individual
families were managed separately (El-Kassaby and Thomson 1996).
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SECTION VIII. SUMMARY
Douglas-fir is one of the most important and valuable timber species globally. Its wood is moderately
heavy and hard, and exceptionally strong. It is a source of wood for both lumber and pulp, and used for
structural purposes, in shipbuilding, and in the production of items such as laminated beams and interior
and exterior finishing, boxes, railway ties, and when impregnated with a preservative, in piling and decking
for marine structures. Douglas-fir is also grown for seasonal Christmas trees, and as an ornamental.
Across its native range in western North America, Douglas-fir is a long-lived and ecologically
important species. It is a seral species in wet and cool climates, and a fire-adapted climax species in dry
and warm climates. Because of its rapid growth rate, it produces a higher volume of wood sooner than
many of its associates, and is valuable as an exotic plantation species in many temperate regions. It has
moderate nutrient requirements and is easy to regenerate and grow. The ecology of Douglas-fir is diverse,
in keeping with its large geographical distribution. It may grow in pure, single-storied, even-aged stands as
well as in multi-aged and multi-storied stands. It is associated with many softwood and hardwood species
in diverse ecosystems throughout a considerable range of climatic zones. Douglas-fir is also a major tree
species in critical watersheds and in many scenic and recreational areas. It is a component of a very large
area of wildlife habitat, and is widely associated with grazing and range allotments.
Douglas-fir has very high levels of genetic diversity, and this variation represents an important
resource. Genetic clines are strong, related primarily to environmental gradients in temperature, but also to
moisture. There is a lack of consensus on how narrowly populations are adapted, and thus at what
geographic scale they should be managed. Genetic diversity in this species is fairly well protected in most
regions, both in situ and ex situ, and potential conservation gaps in the northernmost and northwestern
portions of the range have been assessed. Breeding programs, particularly for the coastal variety, are large
and well into the second generation of domestication. Selective breeding is increasing growth rate while
maintaining the stem form and wood quality that make this such a desirable timber species. New cloning
technologies, primarily somatic embryogenesis, allow for consideration of clonal strategies for improving
this species.
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