article id 547, category Commentary
Introduction. Disturbance dynamics in boreal forests: defining the ecological basis of restoration and management of biodiversity. Silva Fennica vol. 36 no. 1 article id 547. https://doi.org/10.14214/sf.547
Category: Research article
article id 568, category Research article
Anthropogenic effects on understorey vegetation in Myrtillus type urban forests in southern Finland. Silva Fennica vol. 36 no. 1 article id 568. https://doi.org/10.14214/sf.568
The growth of urban population in Finland has resulted in increased fragmentation of urban forests and consequently increased recreational pressure on these forests. The effects of fragmentation and trampling on the ground and field layer vegetation were studied in mesic Myrtillus type Norway spruce-dominated urban forest stands of varying size in the greater Helsinki area. The number of residents living in the vicinity of the forest stands was an important factor affecting the understorey vegetation in urban forests. The cover of understorey vegetation in urban forests was remarkably lower than in rural areas, especially the ground layer cover, e.g. cover of Pleurozium schreberi, was significantly lower in urban forests than in the reference areas. Thus, the ground layer proved to be most susceptible to trampling. In the field layer, the cover of dwarf shrubs, especially of Vaccinium myrtillus, was lower in deteriorated than in undeteriorated urban forest stands.
article id 567, category Research article
Influence of forest composition on understory cover in boreal mixedwood forests of western Quebec. Silva Fennica vol. 36 no. 1 article id 567. https://doi.org/10.14214/sf.567
Forest overstory composition influences both light and nutrient availability in the mixed boreal forest. The influence of stand composition on understory cover and biomass was investigated on two soil types (clay and till deposits). Four forest composition types were considered in this study: aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), jack pine (Pinus banksiana Lamb.) and a mixture of balsam-fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss). The cover of all understory species was recorded while the biomass of two important and ubiquitous species was measured: mountain maple (Acer spicatum Lam.) of the shrub layer and large-leaved aster (Aster macrophyllus L.) of the herb layer. Soil analyses were conducted to evaluate the influence of overstory composition on understory biomass through its influences on soil characteristics. Analyses of variance showed a significant effect of forest canopy type on mountain maple biomass, understory cover and shrub cover but not on herb cover and large-leaved aster biomass. Path analysis was performed to explore the relationships between canopy type, nutrient availability and understory biomass. Contrary to what was expected, the variation in plant biomass associated with forest composition was weakly related to soil nutrient availability and more strongly related to stand structural attributes.
article id 566, category Research article
Effects of clearcut edges on trees in the sub-boreal spruce zone of Northwest-Central British Columbia. Silva Fennica vol. 36 no. 1 article id 566. https://doi.org/10.14214/sf.566
Clearcut-forest boundaries were evaluated for their effects on mature and regenerating trees in the northern interior of British Columbia, Canada. Two hundred and eighteen rectangular plots measuring 200 m2 each were arrayed in transects across 12 cutblock edges created 9 to 21 years earlier, with the wall of standing timber facing either north or south. The density of canopy trees on the inner edge was found to be reduced by 19% (on north-facing edges) to 46% (on south-facing edges) from average densities found in forest interiors. This reduction was primarily due to windthrow after logging, which was elevated by 27% (over interior background levels) at north-facing edges, and by 216% at south-facing edges. Of the trees situated within 10 m of south-facing cutblock edges, 11% of the Pinus contorta, 18% of the Abies lasiocarpa, and 42% of the Picea engelmannii x glauca trees have apparently collapsed, primarily those having height-to-dbh ratios greater than 71:1. As a result, irradiance in the forest understory was elevated (over interior levels) at south-facing edges to distances of approximately 65 to 70 m into the forest. Increased irradiance from adjacent cutblocks enhanced the understory growth of Picea for approximately 60 m into the inner edge of forests, 75 m for Abies. Mature Pinus trees on south-facing edges showed an unexplained 48% decrease in radial growth compared to average growth rates in forest interiors, an effect that was detectable up to 45 m into the forest. Elevated densities of conifer seedlings were evident for up to approximately 70 m into clearcuts from north-facing forest edges. Seedling growth in clearcuts was largely unaffected by shade from stand edges. Though the extent of edge effects varies considerably with the statistical techniques used to detect them, it appears that opening effects on trees can extend between 40 and 120 m into this forest type, while canopy effects reach shorter distances into clearcuts.
article id 565, category Research article
Silvicultural disturbance severity and plant communities of the southern Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 565. https://doi.org/10.14214/sf.565
Boreal forest ecosystems are adapted to periodic disturbance, but there is widespread concern that conventional forest practises degrade plant communities. We examined vegetation diversity and composition after clearcut logging, mechanical and chemical site preparation in eight 5- to 12-yr old studies located in southern boreal forests of British Columbia and Quebec, Canada to find useful indicators for monitoring ecosystem integrity and to provide recommendations for the development and testing of new silvicultural approaches. Community-wide and species-specific responses were measured across gradients of disturbance severity and the results were explained in terms of the intermediate disturbance hypothesis and a simple regeneration model based on plant life history strategies. Species richness was 30 to 35% higher 5 to 8 years after clearcut logging than in old forest. Total and vascular species diversity generally peaked on moderately severe site treatments, while non-vascular diversity declined with increasing disturbance severity. On more-or-less mesic sites, there was little evidence of diversity loss within the range of conventional silvicultural disturbances; however, there were important changes in plant community composition. Removing soil organic layers caused a shift from residual and resprouting understory species to ruderal species regenerating from seeds and spores. Severe treatments dramatically increased non-native species invasion. Two important challenges for the proposed natural dynamics-based silviculture will be 1) to find ways of maintaining populations of sensitive non-vascular species and forest mycoheterotrophs, and 2) to create regeneration niches for disturbance-dependent indigenous plants without accelerating non-native species invasion.
article id 564, category Research article
The regeneration niche of white spruce following fire in the mixedwood boreal forest. Silva Fennica vol. 36 no. 1 article id 564. https://doi.org/10.14214/sf.564
Early establishment of white spruce (Picea glauca) in mixedwood boreal forest stands following fire was examined at several times-since-fire (1-, 2-, 4-, 6-, 14-years). Abiotic and biotic conditions in the stands were assessed at two scales, tree plot (5 m x 5 m) and microsite (1 m x 1 m), along with presence, density and height of white spruce seedlings. Germination and survival of seed sown 1- and 4-years post fire were quantified. Survival and growth of nursery-grown seedlings, and mycorrhizal colonization, survival and growth of sterile seedlings, planted 1-year post-fire were assessed. At the tree plot scale, presence of white spruce seedlings 1-year post-fire could be reliably predicted by organic layer depth and distance to and strength of seed source. In contrast, none of the biotic or abiotic factors measured was strongly correlated with occurrence or density of white spruce seedlings 6- and 14- years post-fire. At the microsite scale, seedling recruitment immediately post-fire was limited to a distinct subset of available microsites (greater % cover of downed wood and moss, lower % cover of litter and herbaceous vegetation). Likewise, seedling occurrence in older burns was associated with distinct microsite conditions; although this was more likely an effect of white spruce presence, rather than the cause. Less than 3% of seed sown 1 yr post-fire survived to become 1yr old germinants, survival was 41% over the next three years. Availability of suitable regeneration microsites declines rapidly with time-since-fire; less than 0.3% of seed sown 4 yrs post-fire survived one year. High rates of mycorrhizal colonization were found on white spruce seedlings planted 1-year post-fire, including early and late stage fungal species. Microsite characteristics were only weakly correlated with mycorrhizal fungal communities. We propose that immediate post-fire recruitment of white spruce is a key process in mixedwood boreal succession.
article id 563, category Research article
Spatial ecology of the three-toed woodpecker in managed forest landscapes. Silva Fennica vol. 36 no. 1 article id 563. https://doi.org/10.14214/sf.563
The effects of landscape structure and forestry on the abundance and dynamics of boreal forest bird species have been studied widely, but there are relatively few studies in which the spatial structure and quality of the landscape have been related to the spatial ecology of bird species. In this paper, we present methods to measure territory and landscape quality for the three-toed woodpecker (Picoides tridactylus) and similar territorial forest bird species based on data from the Finnish multi-source national forest inventory and metapopulation theory. The three-toed woodpecker was studied with territory mapping within an area of 340 square km in southern Finland in 1987–2000. Altogether 195 breeding territory sites were observed. The spatial occurrence of the territories was aggregated, and the highest densities were observed in spruce-dominated old-growth forest areas. Both territory and landscape quality had significant consequences for the occurrence of the three-toed woodpecker. The spatial patterning and permanence of breeding and non-breeding territories were influenced by a combination of spatial dynamics of the species and the quality of the landscape, the latter being much influenced by forestry. The landscape-level spatial occurrence of the three-toed woodpecker in the study area may represent source-sink dynamics. The results of this paper suggest the presence of threshold values at different spatial scales, which may determine the occurrence of the three-toed woodpecker and similar species in managed forest landscapes.
article id 562, category Research article
A method for generating stand structures using Gibbs marked point process. Silva Fennica vol. 36 no. 1 article id 562. https://doi.org/10.14214/sf.562
Stand growth modelling based on single tree responses to their surroundings requires a description of the spatial structure of a stand. While such detailed information is rarely available from field measurements, a method to create it from more general stand variables is needed. A marked Gibbs point potential theory combined with Markov chain Monte Carlo (MCMC) random process was used to create a spatial configuration for any given number of trees. The trees are considered as charges rejecting each other and building ‘potential energy’. As an analogue of the potential energy in physical systems, the potential of a stand is defined in terms of size-dependent tree-to-tree interactions that can be thought of as related to resource depletion and competition. The idea that bigger trees induce larger potentials brings 3-dimensional effects into the system. Any feasible spatial structure is a state of the system, and the related potential can be calculated. The probability that a certain state occurs is assumed to be a decreasing function of its potential. Because more regular structures have lower potentials, by adjusting the steepness of the probability distribution the spatial structure can be allowed to have a lot of randomness (naturally regenerated stands) or forced to be very regular (planted stands). The MCMC algorithm is a numerical method of finding stand configurations that correspond to the expected level of the potential, given the size distribution of trees and the shape of the probability density function. The method also allows us to take into account spatial variation in the terrain. Some spots can be defined to have lower basic potential than others (ditch, planting furrow, etc.) in order to create areas of higher than average stocking density. A preliminary test of the method was conducted on two measured stands. The results suggest that the method could provide an efficient and flexible means of mimicking variable stand structures.
article id 561, category Research article
Post-fire development of canopy structure and composition in black spruce forests of Abitibi, Québec: a landscape scale study. Silva Fennica vol. 36 no. 1 article id 561. https://doi.org/10.14214/sf.561
Fire reconstruction and forest inventory maps provided an opportunity to study changes in stand-level characteristics following fire using a data set comprised of all forest stands of fire origin in an area of over 10 000 km2. We assigned the date of the most recent fire occurrence to over 31 000 forest stands in an ecoforestry database. We categorized stands on different substrates into age classes to investigate differences in canopy composition, cover and height, and incidence of secondary disturbance. Stands with over 75% Picea mariana (Mill.) BSP dominated all age classes on organic sites. On other substrates, there was a change in canopy composition from deciduous stands and stands dominated by Pinus banksiana Lamb. to Picea mariana stands after about 100 yr. This transition was later for xeric sites. After a peak in canopy cover and height at about 100 yr, there was a decrease in the area occupied by stands with dense, tall canopies. Structural development was slower on less productive sites. There was little incidence of spruce budworm outbreaks. Partial disturbance by windthrow coincided with canopy break-up at 100 yr, but appeared to have little effect on overall canopy structure in later stages. Structural diversity was independent of compositional diversity; on organic sites, stands with similar composition had different canopy structure. Diversity of stands with different composition and structure was greatest in the first 150 yr following fire. Maintaining stands in different stages of structural development on the landscape would serve to maintain regional biodiversity.
article id 560, category Research article
An approach to predicting the potential forest composition and disturbance regime for a highly modified landscape: a pilot study of Strathdon in the Scottish Highlands. Silva Fennica vol. 36 no. 1 article id 560. https://doi.org/10.14214/sf.560
The existing native forests of Scotland are fragmented and highly modified and none are ‘natural’. There is considerable interest in expanding the area of this oceanic boreal forest and restoring forest habitat networks to benefit biodiversity. However, unlike regions with substantial remaining natural forest, it is difficult to provide reference values for forest composition and structure using methods related to historical variability. An alternative approach is to combine models that predict woodland type from knowledge of site conditions, and disturbance regime from knowledge of the disturbance agents (particularly abiotic agents). The applicability of this approach was examined as part of a public participatory planning exercise in a highly managed landscape in Eastern Scotland. Models of site suitability (Ecological Site Classification) and wind disturbance (ForestGALES) were combined to determine potential woodland composition and structure, and derive options for native woodland expansion. The land use of the upper Strathdon catchment is currently dominated by agriculture and planted forests of non-native species, and only small fragments of semi-natural woodland remain (< 0.5% of the land area). Model results indicated that a very substantial proportion of the land area could support woodland (> 90%) but of a restricted range of native woodland types, with Scots pine communities predominant. Structural types likely to be present included wind-induced krummholz (treeline) forest, forest with frequent stand replacement by wind, and also a large area where gap phase (or some other disturbance) would predominate. The merits of the approach are discussed, together with the difficulties of validation, and the implications for the management of existing forests.
article id 559, category Research article
Forest age distribution under mixed-severity fire regimes – a simulation-based analysis for middle boreal Fennoscandia. Silva Fennica vol. 36 no. 1 article id 559. https://doi.org/10.14214/sf.559
A simulation model was used to study the age structure of unmanaged forest landscapes under different fire regimes. Stand age was defined as the age of the oldest tree cohort in a stand. When most fires are not stand-replacing, the theoretical equilibrium stand age distribution is either bell-shaped or bimodal and dominated by old age-classes. Old-growth forests (oldest cohort > 150 y) dominate the landscape unless fires are both frequent and severe. Simulation results and analytical calculations show that if a regime of frequent fires (about every 50 y) maintains landscapes dominated by old-growth forests, then old-growth dominance persists when the number of fires is decreased, despite the associated increase in fire severity. Simulation results were applied to Pinus sylvestris-dominated landscapes of middle boreal Fennoscandia, which according to empirical results were dominated by old-growth forests when fires were frequent during the 19th century. Since the changes in the fire regime can be plausibly explained by changes in the number of human-caused ignitions, old-growth forests have evidently also dominated the landscapes earlier when fires were less frequent. The simulation model is used to produce plausible age distributions of middle boreal Fennoscandian forest landscapes under different historical fire regimes. In summary, the frequency of large-scale disturbance alone predicts forest landscape dynamics poorly, and the roles played by fire severity and residual stands need to be considered carefully. Maintaining and restoring old-growth structures is essential to regaining the natural variability of Fennoscandian forest landscapes.
article id 558, category Research article
Forest age distribution and traces of past fires in a natural boreal landscape dominated by Picea abies. Silva Fennica vol. 36 no. 1 article id 558. https://doi.org/10.14214/sf.558
Forest age distribution and occurrence of traces of past fires was studied in a natural Picea abies -dominated landscape in the Onega peninsula in north-west Russia. Forest age (maximum tree age) was determined and charcoal and fire scars were searched for in 43 randomly located study plots. In 70% of the study plots (30/43) trees older than 200 years existed. The largest 50-year age class consisted of plots with 251–300 year old forests. Traces of fires were found in all types of study plots, in forests on mineral soil as well as on peatlands. However, fire has been a rare disturbance factor, as traces of fires could not be found in 35% of the study plots (15/43). Estimated from the forest age class distribution, the fire rotation time for the whole area has been at least 300 years, but possibly considerably longer. This fire rotation time is much longer than fire history studies (largely based on examination of fire scars) commonly have reported for the average time between successive fires in Fennoscandia and Northwest Russia. The results suggest that the often stated generalisations about the importance and natural frequency of fire disturbance in boreal forests do not apply in landscapes dominated by Picea abies.
article id 557, category Research article
Spatial tree age structure and fire history in two old-growth forests in eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 557. https://doi.org/10.14214/sf.557
Two near natural old-growth forests, one dominated by Picea abies and the other by Pinus sylvestris, were studied for their fire history, and spatial patterns of trees and tree ages. The spatial tree age structure and the disturbance history of the forests were examined by drawing age class maps based on mapped and aged trees and by dating fires based on fire scars, and by using spatial analyses at tree scale. The tree age structures of the Picea and Pinus dominated forests were different, mainly due to differences in fire history and sensitivity of the dominant tree species to fire. Fire histories and tree age structures of both sites have probably been affected by human in the ancient past. However, in the Picea dominated site, the fires had been severe, killing most of the trees, whereas in the Pinus dominated site the severity of fires had been more variable, leaving some Pinus and even Picea trees alive. In the Pinus dominated site, the tree age distribution was multimodal, consisting of two Pinus cohorts, which were established after fires and a later Picea regeneration. The Picea dominated site was composed of four patches of different disturbance history. In the oldest patch, the tree age distribution was unimodal, with no distinct cohorts, while a single cohort that regenerated after severe fire disturbances dominated the three other patches. In both sites the overall spatial patterns of living and dead trees were random and the proportion of spatially autocorrelated variance of tree age was low. This means that trees of different age grew more or less mixed in the forest without forming spatially distinct regeneration patches, even in the oldest patch of Picea dominated Liimatanvaara, well over 200 years after a fire. The results show that detail knowledge of disturbance history is essential for understanding the development of tree age structures and their spatial patterns.
article id 556, category Research article
Tree age distributions in old-growth forest sites in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 556. https://doi.org/10.14214/sf.556
The age and size of trees was sampled and measured on eight sample plots (0.2 ha each) within a Pinus sylvestris -dominated boreal forest landscape in Vienansalo wilderness, Russian Karelia. The fire history of these plots was obtained from a previous dendrochronological study. All the studied sample plots showed a wide and uneven distribution of tree ages, but the shape of the age distributions of trees as well as tree species composition varied substantially. Trees over 250 years of age occurred in every studied plot, despite its small size. This suggests that old Pinus were common and rather evenly distributed in the landscape matrix. The oldest Pinus tree was 525 years of age. The correlations between tree age and size were often weak or even nil. In Pinus the correlation between age and diameter was stronger than that between age and height. In the dominant tree species Pinus and Picea, the largest trees were not the oldest trees. The tree age distributions together with the fire history data indicated that the past fires have not been stand replacing, as many of the older Pinus had survived even several fires. Tree age classes that had regenerated after the last fire were most abundant and dominated by Picea and/or deciduous trees, while the trees established before the last fire were almost exclusively Pinus. The results suggest that periodic occurrence of fire is important for the maintenance of the Pinus-dominated landscape. This is because fire kills most Picea and deciduous trees and at the same time enhances conditions for Pinus regeneration, facilitated by available seed from the continuous presence of old fire-tolerant Pinus trees.
article id 555, category Research article
Amount and diversity of coarse woody debris within a boreal forest landscape dominated by Pinus sylvestris in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 555. https://doi.org/10.14214/sf.555
The amount, variability, quality and spatial pattern of coarse woody debris (CWD) on mineral soil sites was studied within a natural Pinus sylvestris L. dominated boreal forest landscape in Russian Viena Karelia. Data on the total CWD was collected on 27 sample plots (20 m x 100 m) and data on large CWD was surveyed along four transects (40 m wide and up to 1000 m long). The mean volume of CWD (standing and down combined) was 69.5 m3 ha–1, ranging from 22.2 m3 ha–1 to 158.7 m3 ha–1 from plot to plot. On average, 26.9 m3 ha–1 (39%) of CWD was standing dead wood and 42.7 m3 ha–1 (61%) down dead wood. The CWD displayed a wide range of variation in tree species, tree size, stage of decay, dead tree type and structural characteristics, creating a high diversity of CWD habitats for saproxylic organisms. Large CWD was almost continuously present throughout the landscape and its overall spatial distribution was close to random, although a weak autocorrelation pattern was found at distances less than about 50 m. On small spatial scales total CWD showed wide variation up to a sample area of about 0.1 ha, beyond which the variation stabilized. The fire history variables of the sample plots were not related to the amount of CWD. This and the spatial pattern of CWD suggest that the CWD dynamics in this landscape was not driven by fire, but by more or less random mortality of trees due to autogenic causes of death.
article id 554, category Research article
Tree mortality in a Pinus sylvestris dominated boreal forest landscape in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 554. https://doi.org/10.14214/sf.554
Tree mortality and its causes and spatial pattern were examined along four transects (width 40 m, length 2550–3960 m), with a total length of 12 190 m and area of 48.8 ha, in a Pinus sylvestris L. dominated, boreal forest landscape. Tree mortality was determined within a time window of 3 years by identifying those trees (dbh ≥ 10 cm) along the transects that fitted into one of the three categories: 1) current mortality: trees that had died during the year of survey (1998), 2) recent mortality: trees that had died during the year (1997) before the survey year, and 3) predicted mortality: trees that were expected to die during the year (1999) following the survey year. Long-term tree mortality was studied on 10 plots (20 m x 100 m) by dating 87 dead trees using dendrochronological methods. The mean current mortality was 1.4 m3 ha–1 (3.7 trees ha–1). Both the recent and predicted mortalities were also 1.4 m3 ha–1. Mortality was, on the average, higher on peatlands than on mineral soils. The highest mortality was found within an area recently flooded by beavers. Over half of the examined trees (52%) were judged to die without any visible signs of an external abiotic cause. At the landscape scale, tree mortality was continuous although somewhat aggregated in space. Of the 66 dated standing dead Pinus trees, 23 (35%) had died during the 19th century and two during the 18th century, demonstrating that dead Pinus can remain standing for long periods of time before falling. Our results show that autogenic mortality of individual trees or small groups of trees was the predominant mode of disturbance in this Pinus dominated landscape.
Category: Review article
article id 553, category Review article
Natural fire regime: a guide for sustainable management of the Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 553. https://doi.org/10.14214/sf.553
The combination of certain features of fire disturbance, notably fire frequency, size and severity, may be used to characterize the disturbance regime in any region of the boreal forest. As some consequences of fire resemble the effects of industrial forest harvesting, conventional forest management is often considered as a disturbance that has effects similar to those of natural disturbances. Although the analogy between forest management and fire disturbance in boreal ecosystems has some merit, it is important to recognise that it also has its limitations. Short fire cycles generally described for boreal ecosystems do not appear to be universal; rather, important spatial and temporal variations have been observed in Canada. These variations in the fire cycle have an important influence on forest composition and structure at the landscape and regional levels. Size and severity of fires also show a large range of variability. In regions where the natural matrix of the boreal forest remains relatively intact, maintenance of this natural variability should be targeted by forest managers concerned with biodiversity conservation. Current forest management tends to reduce this variability: for example, fully regulated, even-aged management will tend to truncate the natural forest age distribution and eliminate over-mature and old-growth forests from the landscape. We suggest that the development of strategic-level forest management planning approaches and silvicultural techniques designed to maintain a spectrum of forest compositions and structures at different scales in the landscape is one avenue to maintain this variability. Although we use the boreal forest of Quebec for our examples, it is possible to apply the approach to those portions of the boreal forest where the fire regime favours the development of even-aged stands in burns.
article id 552, category Review article
Natural variability of forests as a reference for restoring and managing biological diversity in boreal Fennoscandia. Silva Fennica vol. 36 no. 1 article id 552. https://doi.org/10.14214/sf.552
In Fennoscandia, use of the natural forest as a reference for restoration and management of forest biodiversity has been widely accepted. However, limited understanding of the structure and dynamics of the natural forest has hampered the applications of the natural variability approach. This is especially the case in areas, where the natural forests have almost totally vanished. This review was motivated by the idea that despite these difficulties the essential features of the natural forest can be reconstructed based on biological archives, historical documents, research done in adjacent natural areas, and modeling. First, a conceptual framework for analyzing the relationship between forest structure, dynamics and biodiversity is presented. Second, the current understanding of the structure and dynamics of natural forests at different spatiotemporal scales in boreal Fennoscandia is reviewed. Third, the implications of this knowledge, and gaps in knowledge, on research and on practical restoration and management methods aimed at forest biodiversity conservation are discussed. In conclusion, naturally dynamic forest landscapes are complex, multiscaled hierarchical systems. Current forest management methods create disturbance and successional dynamics that are strongly scale-limited when compared with the natural forest. To restore some of the essential characteristics of the natural forest’s multiscale heterogeneity, diversification of silvicultural and harvesting treatments, as guided by natural disturbance dynamics, is needed to produce more variation in disturbance severity, quality, extent, and repeatability.
article id 551, category Review article
Effects of fire on ectomycorrhizal fungi in Fennoscandian boreal forests. Silva Fennica vol. 36 no. 1 article id 551. https://doi.org/10.14214/sf.551
Fire, the primary natural disturbance factor in Fennoscandian boreal forests, is considered to have exerted major selection pressure on most boreal forest organisms. However, recent studies show that few ectomycorrhizal (EM) fungi appear to have evolved post-fire adaptations, no succession of EM fungi following fire is apparent after low intensity fires, and only two EM fungal taxa exclusively fruit at post-fire conditions. In this paper I review the present knowledge of effects of forest fire on EM fungal communities in Fennscandian boreal forests, put into perspective by a comparison from other parts of the world. Characteristically, these boreal forests consist of less than a handful of tree species, e.g. Scots pine and Norway spruce, while the below ground communities of EM fungi is impressively species rich with presently more than 700 known taxa. Commonly, forest fires in Fennoscandia have been of low intensity, with a considerable portion of the trees surviving and the organic humus layer partly escaping combustion. Hence, EM fungi appear to largely have evolved under conditions characterised by a more or less continuous presence of their hosts. In fact, the composition of EM fungi within a forest appear be more variable due to spatial variation than due to wildfire. However, in areas with high intensity burns and high tree mortality, most EM fungi may locally be killed. Thus, the legacy of EM fungi following wildfire depends on the survival of trees, which determine the potential for mycorrhizal growth, and the combustion and heating of the organic soil, which directly correlate to mortality of mycorrhizas. The questions if and to what degree fires may be of significance for yet unidentified spatiotemporal dynamics of EM fungal populations and communities are discussed. Recent experiments indicate a few EM fungi are favoured by high intensity burn conditions whereas others disappear. The consequences of wildfires in temperate conifer forests differ considerably from those in boreal forests. Wildfires in temperate conifer forests are typically high intensity stand-replacing fires that cause a total combustion of organic layers. Subsequently, pre-fire EM fungal communities are largely eradicated and a succession of post-fire EM fungi is initiated.
article id 550, category Review article
The role of moose as a disturbance factor in managed boreal forests. Silva Fennica vol. 36 no. 1 article id 550. https://doi.org/10.14214/sf.550
We review the interactions between moose (Alces alces) and native tree species in Fennoscandia. The Fennoscandian boreal forests have been intensively managed for wood production over decades. Moose population density is also relatively high in these northern forests. Forest management affects habitat characteristics and food resources from regeneration to final harvest, with the most significant effects occurring early in the stand development. The plant-animal interactions found in such a situation may be different from what has been observed in natural boreal forests with low densities of moose (e.g. in North America). The strong focus on Scots pine (Pinus sylvestris) in forest regeneration in conjunction with a homogenisation of the landscape structure by clear-cutting has favoured moose. Forest development is controlled by man from regeneration to final harvest, and in relation to human-induced disturbances the disturbance by moose is relatively small, but occurs on different spatial levels. At the landscape level, the most prominent effects of moose seem to be suppression and/or redistribution of preferred browse species. At the forest stand level moose primarily induce spatial heterogeneity by browsing patchily and exploiting existing gaps. At the tree level, moose damage trees and lower timber quality, but also create substrate types (e.g. dead and dying wood) valuable for many organisms. Co-management of moose and forest requires good monitoring programmes for both plants and animals, as well as extensive ecological knowledge on the relations between moose and their food plants on different spatial levels.
article id 549, category Review article
Natural disturbance dynamics in the boreal forests of European Russia: a review. Silva Fennica vol. 36 no. 1 article id 549. https://doi.org/10.14214/sf.549
In the European part of the Russian boreal zone the dynamics of pristine forests (taiga) has been studied by several generations of researchers. Many studies have examined the patterns and role of fire, windthrow, insect outbreaks and other natural disturbances. An attempt is made to provide a brief review of these studies. The reviewed studies show that lightning strikes were the only natural source of fires in taiga. The frequency of fires varied in various types of pristine landscape from 1–2 per century to 1–2 per millennium. Fires maintained a dynamic equilibrium between compositionally different forest communities or their certain ratio and areal occurrence. Fires favored the regeneration and recovery of pine forests and prevented the replacement of shade-intolerant species (e.g. pine) by shade-tolerant ones (e.g. spruce). Taiga forests generally displayed a mosaic pattern that varied from pioneer plant communities, growing in open burns, to climax communities that were extremely seldom affected by fire. The reviewed studies suggest that fires were a powerful ecological factor in pristine taiga, being largely responsible for the structure and spontaneous dynamics of forest communities. Windfalls were also common in pristine taiga landscapes and they regulated spontaneous dynamics in a gap-mosaic regime, which is most characteristic of spruce forests.
article id 548, category Review article
Dynamic interactions between forest structure and fire behavior in boreal ecosystems. Silva Fennica vol. 36 no. 1 article id 548. https://doi.org/10.14214/sf.548
This paper reviews and synthesizes literature on fire as a disturbance factor in boreal forests. Spatial and temporal variation in the biophysical environment, specifically, vegetative structure, terrain, and weather lead to variations in fire behavior. Changes in slope, aspect, elevation, and soil affect site energy and water budgets and the potential plant community. These terrain features also have a major influence on fire-caused disturbance through their role in determining moisture conditions and flammability of fuels on hourly, seasonal, and successional time-scales. On fine time scales (minutes to hours), changes in weather, specifically wind and relative humidity, significantly affect a fire’s intensity and aboveground effects. Normal seasonal changes in dryness and periodic drought influence fire intensity and severity principally by affecting the depth of burn and belowground effects. On decades-long time scales changes in vegetative structure affect the mass of fuel available for burning and therefore the potential energy that can be released during a fire. The severity of fire varies in time and space depending not only on the biophysical environment, but also on the location on the fire’s perimeter (head vs. flank vs. rear). Spatial and temporal variation in severity within a fire can have long-lasting impacts on the structure and species composition of post-fire communities and the potential for future disturbances. Characteristic temperature histories of ground, surface, and crown fires are used to illustrate variations in fire severity. A soil-heating model is used to illustrate the impact of varying depth of burn on the depth at which various fire effects occur in the soil profile. A conceptual model is presented for the effects of fire severity on fire-plant regeneration interactions. The conceptual model can be used by restoration ecologists to evaluate the differential effects of controlled or prescribed fires and wildfires and to plan and implement fire treatments to conserve biodiversity.
Category: Research note
article id 569, category Research note
Occurrence of fires in the eastern Saariselkä area, north-west Russia. Silva Fennica vol. 36 no. 1 article id 569. https://doi.org/10.14214/sf.569
The occurrence of fires was studied in the eastern Saariselkä area, North-West Russia, by using satellite images and topographical maps. In total, more than 330 burned areas were pinpointed in the study area of 4770 km2. Old burns were concentrated in the eastern part of the study area, but young burns were more common in the west. Sites affected by fires in the more recent past were much smaller than those burnt over earlier. The abundance of burns along rivers and the border surveillance road provided evidence of human impact. The most significant changes in the landscape were found in the eastern part of the study area, where spruce forests had been replaced by birch woodlands.
Category: Discussion article
article id 573, category Discussion article
Boreal carabid beetles (Coleoptera, Carabidae) in managed spruce forests – a summary of Finnish case studies. Silva Fennica vol. 36 no. 1 article id 573. https://doi.org/10.14214/sf.573
article id 572, category Discussion article
Principles of ecological restoration of boreal forested ecosystems: Finland as an example. Silva Fennica vol. 36 no. 1 article id 572. https://doi.org/10.14214/sf.572
article id 571, category Discussion article
Using nature’s template to best advantage in the Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 571. https://doi.org/10.14214/sf.571
article id 570, category Discussion article
Scale, the dynamic stability of forest ecosystems, and the persistence of biodiversity. Silva Fennica vol. 36 no. 1 article id 570. https://doi.org/10.14214/sf.570