Forest Ecology and Management 250 (2007) 89–95 www.elsevier.com/locate/foreco Fire history and tree species composition in managed Picea abies stands in southern Finland: Implications for restoration Tuomo Henrik Wallenius a,*, Saara Lilja b, Timo Kuuluvainen b a Finnish Forest Research Institute, Kolari Research Unit, Muoniontie 21, FI-95900 Kolari, Finland b Department of Forest Ecology, PL 27, FIN-00014 University of Helsinki, Finland Abstract We studied the fire history of 24 managed Picea abies-dominated stands in southern Finland using dendrochronological dating of fire scars in old stumps. Forests in the study area have been heavily utilized in many ways for centuries for swidden cultivation, tar burning, forest pasturage and pasture burning. Old charred stumps of Pinus sylvestris were found in every stand although in nine of them the stumps were too decayed to provide a sample that could be dated. In the 17th and 18th centuries, forests burned at intervals of ca. 50 years on average. The last fires in the study plots occurred in the latter half of the 19th century. Based on the presence of the old Pinus stumps, past frequent fires and historical documents, it can be judged that forests were Pinus-dominated in the 17th and 18th centuries. Around the middle of the 19th century a gap occurred in the annual tree ring chronologies of all study plots. This suggests that large coniferous trees were absent at that time. The currently dominating Picea populations regenerated at the beginning of the 20th century. Our results demonstrate that in an area where human impact on forests has been variable, pervasive and long-lasting, the goal of forest restoration can be very different depending on the choice of reference period. We conclude that for defining restoration goals, knowledge of local forest history is needed. # 2007 Elsevier B.V. All rights reserved. Keywords: Charred stumps; Forest fire; Human influence; Forest structure; Norway spruce; Prescribed burning 1. Introduction As a response to the quest for multi-purpose use of forests and conservation of biodiversity, several approaches for restoration and more ecological forest management have been proposed (Lindenmayer and Franklin, 2002; Stanturf and Madsen, 2005). The principle behind many of these approaches is that in order to prevent losses of biodiversity, human actions in forests should mimic natural disturbances (Bergeron et al., 2002; Kuuluvainen, 2002). Since in the boreal forest, fires are suggested to be the most important natural disturbance, one popular idea is to use the past occurrence and effects of forest fires as a natural range of variability template for forest management and restoration (Angelstam, 1998; Landres et al., 1999; Granström, 2001; Bergeron et al., 2002; Kuuluvainen et al., 2005). In the past, forest fires have been frequent over most of Fennoscandia, and stands have usually burned at intervals from * Corresponding author. Tel.: +358 10 211 35 38. E-mail address: Tuomo.Wallenius@Metla.fi (T.H. Wallenius). 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.03.016 ca. 50 to 100 years (Zackrisson, 1977; Niklasson and Granström, 2000; Wallenius et al., 2004). The shortest fire intervals have been recorded in southern Sweden, where before the 1770s forests burned every 20 years on average (Niklasson and Drakenberg, 2001). However, in P. abies (L.) Karst.dominated forests, and in northern areas in general, fires have been rare and fire cycles can range up to a few hundred years (Engelmark, 1984; Wallenius et al., 2005). In southern and central Fennoscandia, human activity has strongly affected past fire frequencies and forest structures (Wallenius et al., 2004; Groven and Niklasson, 2005). During the most intensive swidden cultivation period (ca. 1500–1850), frequent forest fires increased the proportion of fire tolerant P. sylvestris L. and decreased the fire intolerant Picea (Pitkänen et al., 1999). At present fires are very rare in Fennoscandia because of more than a century of pervasive forest management and related efficient fire prevention. Due to the lack of fires, late successional species, such as Picea, have again gained ground from early successional Pinus, Betula and Populus (Niklasson and Drakenberg, 2001; Kouki et al., 2004). This change in tree species composition has also been observed in nature conservation areas (Haapanen and Siitonen, 1978; Bradshaw, 90 T.H. Wallenius et al. / Forest Ecology and Management 250 (2007) 89–95 1993; Lilja and Kuuluvainen, 2005). Similar species compositional shifts in the absence of fire have been reported from unmanaged forests in North America (Minnich et al., 1995; Lesieur et al., 2002). Another important reason for changes in tree species composition was past selective cutting, which concentrated on large-diameter Pinus trees (Sarvas, 1944). Thus, particularly managed forests lacked large-diameter trees, which are a characteristic feature of near-natural forests (Linder and Östlund, 1998; Lilja and Kuuluvainen, 2005). An understanding of historical or natural fire regimes and stand structure is needed for the use of fire in restoration and ecologically sustainable forest management. Because fire frequencies have considerably varied in time and space between different landscapes and forest types, it is necessary to acquire local knowledge of the historical fires of each area to be restored (Angelstam, 1998). In addition, it is important to estimate the past human influence on fire regimes (Wallenius et al., 2004, 2005; Groven and Niklasson, 2005). The first aim of the study was to reconstruct the fire history of managed P. abies-dominated stands in southern Finland in the Lammi and Padasjoki municipalities. Secondly, based on this information and historical records, we make deductions about the likely past tree species composition and structure of the stands. Finally, we discuss the implications of our findings for forest restoration in southern Finland. 2. Material and methods 2.1. Study area The study was carried out in the Lammi and Padasjoki municipalities (618190 N, 25860 E) in southern Finland. The region is located in the southern boreal vegetation zone (Ahti et al., 1968). The average temperature is about 17 8C in July and 8 8C in January (National Board of Survey, 1987). Yearly rainfall totals 650 mm on average, most of which precipitates during summer and autumn. Soils are mostly podzolic soils on basal tills (National Board of Survey, 1990). P. abies is the dominating tree species in the landscape, although mixed forests and P. sylvestris forests are also common. According to forestry statistics for the Häme-Uusimaa district, Picea makes about 54%, Pinus 27% and Betula spp. 14% of the volume of the growing stock (Finnish Forest Research Institute, 2003). In the study area, the proportion of the stands older than 80 years is about 1:4 in the forested area (Korhonen et al., 2000). In the past, peatlands covered a bit more than 10% of the land area of the districts, but most of the mires have been drained over the last 50 years (Finnish Forest Research Institute, 2003). At present, less than 5% of the original peatlands is untouched (National Board of Survey, 1990). Since WWII the landscape has been shaped by intensive forestry characterized by standwise clear cutting and even-aged stands. The forest land is mostly privately owned, and the mean stand size is only a few hectares. This makes a fragmented landscape dominated by small even-aged stands of different ages but younger than 100 years (Kuuluvainen et al., 2005). The stands used in this study were originally selected for an experimental study of forest restoration (Lilja et al., 2005). The samples for the fire history study were collected before forest restoration treatments (Lilja et al., 2005). Altogether 24 stands were found in forestry databases and selected using the following criteria: mature managed Picea-dominated stands, area 1–3 ha, and Vaccinium myrtillus site type (Cajander, 1926). Before acceptance, the stands were visited in the field to check whether they fulfilled the above criteria. The average age of the stands was 83 years (range 61–101 years). All the stands had been managed, but their origin and exact management history is unknown. All the stands were of the V. myrtillus site type (MT), but five stands had other characteristics, for example, a small patch of the more fertile Oxalis myrtillus site type (OMT) (Cajander, 1926). Although Picea-dominated the stands, other tree species were present, including Betula spp., Populus tremula L., and Pinus. In addition, Sorbus aucuparia L. and Juniperus communis L. occurred in the sapling layer. 2.2. Past human influence in the region Southern Finland was inhabited 9000 years ago, soon after the retreat of ice shields (Huurre, 2001). The first people were nomadic tribes who survived by hunting, fishing and gathering berries and mushrooms. The oldest signs of agriculture in Koski, the neighboring municipality of Lammi, date back to 3400 BP (Tolonen, 1978). In Lammi, swidden cultivation appears to have started about 1800 BP (Huttunen, 1980). Along with the increasing human population, agriculture escalated in the 15th century, and gradually the majority of crops were cultivated on permanent fields (Tolonen, 1978; Huttunen, 1980). Nevertheless, in the mid 19th century, swidden cultivation was still very common in Lammi and Padasjoki, and about half of the forest soils were considered as ‘‘burn beaten land’’ (Heikinheimo, 1915). After the 1860s swidden cultivation steeply decreased (Tasanen, 2004). Other traditional forest uses in the area consisted of forest pasturage, pasture burning and tar burning (Kaila, 1931a; Tasanen, 2004). Between 1752 and 1772 a sawmill was founded in Nystölä (Kaila, 1931b) (Fig. 1). In 1798 a new sawmill were founded nearby in Arrakoski (Kantonen, 1996). These sawmills situated only 5–20 km from our study plots. The timber for the mills was supplied by selective cutting, which was a widespread method in Finland until the middle of the 20th century. In the 1850s, due to the intensive use of the forests, large areas in southern Finland including the Lammi and Padasjoki municipalities suffered from a lack of timber (Gyldén, 1850). 2.3. Stand structure and fire history In the summer of 2001, tree species composition and stand structure were measured in a randomly located rectangular (20 m  40 m) plot in each 1–3 ha study stand. The height of the trees and the diameter at breast height (for trees with height >2 m) were recorded. In addition, from a 5-m buffer zone T.H. Wallenius et al. / Forest Ecology and Management 250 (2007) 89–95 91 Fig. 1. The study area was located in the southern boreal zone in the Lammi and Padasjoki municipalities. The right-hand figure shows the study plots and dated fire years. The locations of the old sawmills in the 18th century in Arrakoski and Nyystölä are also marked. surrounding the subplots, we measured the height and diameter of the living trees (dbh > 10 cm). The average age of the dominant tree cohort was acquired from the forestry databases of different landowners. The examination of past fires was based on finding firescarred trees from the study plots and their immediate neighborhoods. The aim of the sampling was to reconstruct a fire chronology that is as long as possible. Fire scars were only found in old partly decayed stumps; fire scars were also sought in living trees, but none were found. All fire-scarred stumps, if they were not too decayed, were sampled. In addition, a few stumps without fire scars were sampled in order to get longer tree ring chronologies. Altogether 39 tree stumps were sampled in 18 study plots. Samples were dated by dendrochronological methods. These included the polishing of the tree disks and the final preparation of the surface with a scalpel. Zinc paste was used for better visibility of the annual rings. The widths of the annual rings were measured, and the acquired annual ring sequence was dated using COFECHA software and the master chronology of Helama et al. (2005). For the examination of the fire history, the proportion of burnt areas (computed as a percentage of the study area) and fire cycle (number of years needed to burn an area equal to the study area) were reconstructed for the 17th and 18th centuries, which was the period with good sample coverage. We determined that a stand was burned if it had at least one charred stump with one or more fire scars. For each fire event, the burnt area was determined as the ratio of the number of burnt study plots to the number of unburnt plots. Only those study plots where the annual ring chronology of the plot extended to the year in question were considered. 3. Results The average age of the dominating Picea cohorts in the study stands was 83 years, but as the two samples taken from living Pinus show, the oldest trees could be considerably older (Fig. 3). Nonetheless, there seems to be a gap in the year ring chronologies of at least a few decades between the dated old stumps of Pinus and the present day Picea forest. The volume of the Picea-dominated stands was on average 220 m3/ha (range 171–293 m3/ha). The proportion of deciduous was on average 3.2 m3 (1.5%; range 0–14 m3/ha). Although the forests in the region as well as the selected stands are currently dominated by Picea (Fig. 2), it appears that in the past the tree species composition has been more Pinusdominated. This can be deduced from the fact that there were Fig. 2. Average volume (m3/ha) of different tree species in the study plots before experimental burning and cutting in 2001. Error bars are standard deviations. 92 T.H. Wallenius et al. / Forest Ecology and Management 250 (2007) 89–95 Fig. 3. Tree ring and fire chronologies of different study plots sorted by the first year ring. Black squares denote dated fires on Pinus stumps. The figure is produced with the help of the FHX2 program (Grissino-Mayer, 1995). old charred stumps of Pinus in every study plot, although most of the stumps were too decayed and fragmented to allow dendrochronological dating. In some of the stands with charred Pinus stumps, no living Pinus were present. Datable wood samples from old stumps could be found only in 15 plots (Fig. 3). It was inferred from cut marks and the level end of the stumps that many of them were from the period of selective cutting. Cross-dated year ring chronologies extended from the year 1439 to the present (Fig. 3). The first dated fire occurred in 1468 and the last in 1838. Altogether 48 different fire years were dated. Relatively good coverage of samples only stretched from the beginning of the 17th century to the end of the 18th century. Although many of the plots were close to each other, there were only a few common fire years (Fig. 1). This indicates that fires have been mostly relatively small in the area during the last 400–500 years. The last year rings of most of the dated stumps were charred indicating that there had been fires after the death of the trees. It appears that the last fires in the study plots occurred in the latter half of the 19th century (Fig. 3). During the period 1600–1800 the study plots burned on average four times (Fig. 4), corresponding to a fire cycle of 50 years. However, between 1650 and 1700 the studied forests burned at intervals of about 30 years on average. 4. Discussion Fig. 4. Cumulative area burnt as a percentage of the total study area in the period 1600–1800. In the intensively managed forests of southern Finland, forest restoration has been suggested as a means to protect biodiversity and improve the sustainability of forest management (Kuuluvainen et al., 2005; Lilja et al., 2005). The studied mature Picea-dominated stands were typical managed forests, with low structural complexity, scarcity of dead wood and almost monodominant species composition (Lilja et al., 2005). The rather short fire cycles that we found (Fig. 4) are similar to documented past fire cycles in Pinus-dominated forests in central Finland and northern Sweden, where fires have occurred at intervals of 30–60 years during the period 1600–1800 (Zackrisson, 1977; Lehtonen et al., 1996). Our study stands T.H. Wallenius et al. / Forest Ecology and Management 250 (2007) 89–95 were currently dominated by Picea. However, it can be deduced from the short fire cycles in the 17th and 18th centuries, and from the presence of old Pinus stumps, that at that time the studied stands were not dominated by Picea but rather by Pinus and deciduous trees. Picea is known to usually die in fires, and thus short fire cycles favored thick-barked Pinus and fast-growing, well-dispersing deciduous trees over Pinus (Cajander, 1916; Pitkänen et al., 1999). The short fire cycles in the past also promoted the regeneration and spread of Pinus-dominated forests to more fertile stands previously dominated by Picea (Cajander, 1916). After the cessation of fires in the latter half of the 19th century, Picea thrived better than Pinus because Picea is a stronger competitor, especially in nutrient rich habitats. In addition, the widespread industrial selective cutting of big Pinus at the turn of the 19th and 20th centuries probably contributed to the increase in the proportion of Picea (Sarvas, 1944). Other evidence also supports this change in forest composition. Forest and vegetation inventories carried out in the latter half of the 19th century confirm that the forests of the Lammi–Padasjoki region were Pinus-dominated (Leopold, 1879; Montell, 1879). In addition, palaeoecological pollen studies from lake sediments 20 km to the south of our study sites have shown that Picea populations increased at the beginning of the 20th century (Tolonen, 1978; Huttunen, 1980). Before that the abundance of Picea was low for centuries because of frequent fires. The increase of Picea was made possible by the decrease in the number of fires as well as in annually burnt areas since the mid 19th century (Fig. 3). The decrease in fires is a common and well-documented phenomenon in Fennoscandia and in large areas in central North America. Over most of Finland and Sweden, this decrease occurred between 1860 and 1890 (Kohh, 1975; Zackrisson, 1977; Lehtonen et al., 1996). However, in southern Scandinavia and in southwestern Finland, fires had already obviously stopped a century earlier, between 1750 and 1770 (Tolonen, 1985; Niklasson and Drakenberg, 2001; Groven and Niklasson, 2005). In the 19th century, foresters considered the most important reasons for forest fires to be people who burned the forest on purpose, e.g. pasture burning, or by accident when fires escaped from swidden cultivation, smoldering campfires, etc. (Gyldén, 1853; von Berg, 1859; Sargent, 1884; Blomqvist, 1888). An important reason for the decrease in fires was probably that with the onset of the sawmill industry, timber became a valuable resource (Kohh, 1975; Massa, 1994), and fire was therefore handled more carefully than before. This took place concomitantly with the establishment of forest administration and the forest ranger institution, which started to control the use of forests in the middle of the 19th century (Heikinheimo, 1915; Zackrisson, 1977; Ruuttula-Vasari, 2004). Almost all annual ring chronologies of the sampled Pinus ended by the middle of the 19th century, and many of the last rings were dated before the end of the 18th century (Fig. 3). The present Picea forests regenerated at the beginning of the 20th century. This suggests that there were only a few large coniferous trees in the stands in the middle of the 19th century. 93 Accordingly, the forestry map of Gyldén (1850) indicates that the Lammi and Padasjoki communalities suffered from a lack of large timber, and in some areas even small diameter fire wood was limited. Moreover, the pollen analyses from nearby lakes suggest that the landscape in Lammi and Koski was almost treeless at the turn of the 18th and 19th centuries (Tolonen, 1978; Huttunen, 1980). This situation was also reported by some contemporaries, who were horrified by the devastation of forests in southern Finland (von Berg, 1859). It is obvious that in past centuries the forests of the region were heavily utilized by people, often with little or no consideration of sustainability. Swidden cultivation, tar burning, forest pasturage and pasture burning have directly, or indirectly by increasing the number of fires, drastically affected the forests, structure and composition. Finally, it is likely that since the end of the 18th century the two small sawmills, within 10 km of the nearest study plots, have consumed large quantities of good quality timber from the area. These human actions in concert apparently are the reason for the observed decrease in the coniferous forest cover. 5. Implications for forest restoration In Finland, the goal of forest restoration is traditionally defined as the rehabilitation of natural structures, processes and species of forest ecosystems that have been biologically impoverished by human utilization (Working Group, 2003; Kuuluvainen et al., 2005). This definition is clear, but what is natural can be problematic to define in areas of long-lasting human influence (Lilja and Kuuluvainen, 2005). In our study area, the current managed forest dominated by Picea differed considerably from the more open forest dominated by Pinus and the deciduous trees that prevailed in the area in the 17th– 19th centuries (Leopold, 1879; Montell, 1879; Huttunen, 1980). However, at that time the forest was also far from any natural state because forest fires ignited by humans were frequent and forests were heavily utilized in many ways. Thus, it was a culturally modified forest. Furthermore, it is known from previous studies that some thousands of years back into the past, the forest had very different characteristics, with less human impact and fires, and mixed Picea–Pinus–Betula forests characterized by old trees (Tolonen, 1978; Huttunen, 1980; Kuuluvainen, 2002; Pennanen, 2002). The high variation in past fire cycles and forest structures through time, reflecting different types of human impact, makes it difficult to apply the often suggested natural range of variability approach in restoration and management (Landres et al., 1999). For example, if we take the forest structures and fire regimes that prevailed in southern Finland in the 17th and 18th centuries as a reference for restoration, our goal is a forest state that was strongly culturally modified. However, recreating a historical forest would be difficult as this would require prescribed burn intervals of 30–50 years. Moreover, prescribed burning alone would probably not be enough to restore the culturally modified forests of the 17th and 18th centuries, because widespread forest pasturage also affected the structure and species composition of the forests in the past (Helander, 1949). 94 T.H. Wallenius et al. / Forest Ecology and Management 250 (2007) 89–95 We conclude that for defining restoration goals, knowledge of local forest history is necessary, although setting restoration goals is finally a question of values and policy. However, there is no single true reference point in the past that should be selected as a goal for restoration, but a pragmatic goal could be to rehabilitate important historical and natural structures that sustain biodiversity, including important landscape characteristics such as forest age structure (Pennanen, 2002). Restoration can include rehabilitating both cultural features, familiar to the conservation of habitats related to traditional agriculture, and more natural forest states. Acknowledgements We would like to thank Hanna Karttunen for her assistance in the field. The Emil Aaltonen Foundation, the Maj and Tor Nestling Foundation and the Academy of Finland financed the study. References Ahti, T., Hämet-Ahti, L., Jalas, J., 1968. 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