Stand characteristics and biodiversity indicators along the productivity gradient in boreal forests: Defining a critical set of indicators for the monitoring of habitat nature quality

Abstract

We quantified the effects of anthropogenic disturbances on the structure and biodiversity of boreal forests on acidic soils and created a statistically supported rational set of indicators to monitor the stand “naturalness”. For that, we surveyed various traits of tree layer, understory, herb layer, forest floor and several widely accepted biodiversity epiphytic indicators in 252 old‐aged boreal stands in Estonia, mostly dominated by Scots pine or Norway spruce. Multifactorial general linear model analyses showed that many forest characteristics and potential indicators were confounded by the gradient of soil productivity (reflected by the forest site type), local biogeographic gradients and also by stand age. Considering confounding effects, boreal forests in a near‐natural state have more large‐diameter trees (diameter at breast height >40 cm) and larger variety of diameter classes, higher proportion of spruce or deciduous trees, a larger amount of coarse woody debris in various stages, a more closed tree canopy and denser understory than managed mature forests. By increasing light availability above the field layer, forest management indirectly increases the coverage of herbs and lichens on the forest floor but reduces the alpha‐ and beta‐diversity of herbs and the proportion of graminoids. Human disturbances reduce the relative incidence of many commonly accepted biodiversity indicators such as indicator lichens, woodpeckers, wood‐dwelling insects or fungi on trees. The test for the predictive power of characteristics reacting on disturbance revealed that only a fraction of them appeared to be included in a diagnostic easy‐to‐apply set of indicators to assess the nature quality of boreal forest: the amount of dead wood, the proportion of deciduous trees, the presence of specially shaped trees and woodpeckers and, as an indicator of disturbances, the forest herb Melampyrum pratensis. Many of these indicators have already been implemented in practice.     

Forests regenerating after clear-cutting function as habitat for bryophyte and lichen species of conservation concern

The majority of managed forests in Fennoscandia are younger than 70 years old but yet little is known about their potential to host rare and threatened species. In this study, we examined red-listed bryophytes and lichens in 19 young stands originating from clear-cutting (30-70 years old) in the boreal region, finding 19 red-listed species (six bryophytes and 13 lichens). We used adjoining old stands, which most likely never had been clear-cut, as reference. The old stands contained significantly more species, but when taking the amount of biological legacies (i.e., remaining deciduous trees and dead wood) from the previous forest generation into account, bryophyte species number did not differ between old and young stands, and lichen number was even higher in young stands. No dispersal effect could be detected from the old to the young stands. The amount of wetlands in the surroundings was important for bryophytes, as was the area of old forest for both lichens and bryophytes. A cardinal position of young stands to the north of old stands was beneficial to red-listed bryophytes as well as lichens. We conclude that young forest plantations may function as habitat for red-listed species, but that this depends on presence of structures from the previous forest generation, and also on qualities in the surrounding landscape. Nevertheless, at repeated clear-cuttings, a successive decrease in species populations in young production stands is likely, due to increased fragmentation and reduced substrate amounts. Retention of dead wood and deciduous trees might be efficient conservation measures. Although priority needs to be given to preservation of remnant old-growth forests, we argue that young forests rich in biological legacies and located in landscapes with high amounts of old forests may have a conservation value.     

Macrolichen diversity as an indicator of stand age and ecosystem resilience along a precipitation gradient in humid forests of inland British Columbia,Canada

The distributional ecology of 87 macrolichens is reported from 14 unmanaged mid-seral and old forest stands along a precipitation gradient in south-central British Columbia. We used a combination of univariate and multivariate statistics to investigate the role of forest structure and stand age in the distribution of epiphytic macrolichens in interior cedar-hemlock forests. Old forests support a higher number of species; although mean species richness is not significantly different between the two age classes. Terricolous and epixylic community structure is correlated with stand age and log characteristics, but the epiphtytic community is not. Epiphytic community structure is strongly associated with precipitation in the old stands, but not in the mid-seral stands. Old forests at the wetter end of the precipitation gradient contained several old-growth associated species, all of which are hygrophytic. Most epiphytic macrolichens associated with old forests are not dependent on specific structural attributes. However, western red cedar (Thuja plicata Donn ex D. Don) harbors the greatest number of arboreal macrolichen species by far in these unmanaged stands and should, therefore, be considered a key indicator in managed forests. Our study suggests that most macrolichen species found in old forests can also occur in 70- to 165-year-old forests dating from stand-replacing fires. Old forests, however, clearly provide important habitat for oceanic epiphytes at the edge of their ecological range in the interior of British Columbia. Our findings illustrate that the macrolichen flora in wet toe-slope stands in humid inland British Columbia has a high level of resilience following disturbance under natural succession conditions. It also underlines the point that some species, like Lobaria pulmonaria, are good indicators of old-growth forests in certain regions but not in others, suggesting a careful use of the term old-growth dependence.     

Role of the Siberian flying squirrel as an umbrella species for biodiversity in northern boreal forests

One of the potentially useful indirect shortcut methods in biodiversity conservation is the umbrella species concept. An umbrella species can be seen relatively demanding for the size of the area and probably also for certain habitat types: conservation management for the umbrella species would thus encompass other species preferring similar habitats but with smaller area requirements. As such, it has a comprehensive spatial aspect for landscape planning. We tested the role of the Siberian flying squirrel (Pteromys volans) as an umbrella species for wood dependent species among red-listed and old-growth forest associated polypores, epiphytic lichens and beetles. Flying squirrels inhabit home ranges of several to tens of hectares, and prefer mature spruce-dominated (Picea abies) mixed forests, which often have high amounts of dead wood. We carried out species surveys and trappings during 1 year from 20 mature spruce-dominated forest stands (altogether 162 ha), of which 12 were occupied by the flying squirrel. The amount of dead wood was higher in occupied stands than in unoccupied stands. We also found a tendency for a higher number of species and number of records in occupied stands, a relationship mostly due to the polypore species. The presence of the flying squirrel may reflect the habitat availability for species depending on dead and living wood, and assist in site selection of conservation areas. We suggest that the flying squirrel has potential as an umbrella species to partly enhance maintenance of biodiversity in northern boreal forests in Finland.     

Positive edge effects on forest-interior cryptogams in clear-cuts

Biological edge effects are often assessed in high quality focal habitats that are negatively influenced by human-modified low quality matrix habitats. A deeper understanding of the possibilities for positive edge effects in matrix habitats bordering focal habitats (e.g. spillover effects) is, however, essential for enhancing landscape-level resilience to human alterations. We surveyed epixylic (dead wood inhabiting) forest-interior cryptogams (lichens, bryophytes, and fungi) associated with mature old-growth forests in 30 young managed Swedish boreal forest stands bordering a mature forest of high conservation value. In each young stand we registered species occurrences on coarse dead wood in transects 0-50 m from the border between stand types. We quantified the effect of distance from the mature forest on the occurrence of forest-interior species in the young stands, while accounting for local environment and propagule sources. For comparison we also surveyed epixylic open-habitat (associated with open forests) and generalist cryptogams. Species composition of epixylic cryptogams in young stands differed with distance from the mature forest: the frequency of occurrence of forest-interior species decreased with increasing distance whereas it increased for open-habitat species. Generalists were unaffected by distance. Epixylic, boreal forest-interior cryptogams do occur in matrix habitats such as clear-cuts. In addition, they are associated with the matrix edge because of a favourable microclimate closer to the mature forest on southern matrix edges. Retention and creation of dead wood in clear-cuts along the edges to focal habitats is a feasible way to enhance the long-term persistence of epixylic habitat specialists in fragmented landscapes. The proposed management measures should be performed in the whole stand as it matures, since microclimatic edge effects diminish as the matrix habitat matures. We argue that management that aims to increase habitat quality in matrix habitats bordering focal habitats should increase the probability of long-term persistence of habitat specialists.     

Diversity of wood-decaying fungi under different disturbance regimes—a case study from spruce mountain forests

Rapid destruction of forest habitats has led to the establishment of protected areas in formerly managed forests with the aim of restoring biodiversity. Conservation in spruce-dominated reserves is often contradicted by salvage logging after insect outbreaks. Here we study the community characteristics of wood decaying fungi in a high montane Norway Spruce forest with three different management types: (1) a formerly managed area disturbed by a large-scale bark beetle outbreak, (2) an area with continuous salvage logging, and (3) an old-growth forest. Bark beetle activity in the disturbed area resulted in downed wood amounts comparable to those of the old-growth forest. However, species accumulation curves for the disturbed forest were more similar to those of the logged forest than to those of the old-growth forest. This arose because of differences in the diversity of wood decay classes; wood decay in the disturbed forest was more homogeneous. Logs in the disturbed forest originated almost exclusively from bark-beetle-infested trees, but the causes of tree mortality in the old-growth forest were manifold. Although most red-listed species were clearly confined to old-growth forest, Antrodiella citrinella was most abundant in the disturbed forest. Our analysis furthermore showed that the between stand scale is the most effective unit for diversity wood-decaying fungi. We therefore suggest a conservation strategy for preserving old-growth forests and establishing protected forest stands to enhance structural heterogeneity in spruce-dominated forests. For this, a careful screening of protected areas throughout Europe is necessary to provide managers with guidelines for conservation.     

Spontaneous restoration of epiphytic lichen biota in managed forests planted on habitats typical for temperate deciduous forest

The study examines the changes of epiphytic lichen diversity in differently aged stands developing after clear cutting and pine planting on fertile habitats typical for deciduous forests. The study was conducted within one large complex consisting of pine, mixed pine-hornbeam and typical old oak-linden-hornbeam forests in northern Poland. Epiphytic lichens were recorded in 50 study plots randomly selected within 5 forest stand classes of a different structure and age, ranging from 80 to over 220 years. Altogether 143 lichen species were recorded, of which only 41 were entirely nonspecific, and were occurring in all the studied forest stand classes. Significant differences in lichen species richness between stand classes were found and the number of species increases with the forest age. Lichen species composition also differs and its changes progress towards restoration of lichen biota typical for deciduous forest consistent with the habitat. The age of the forest has the most significant effect on the biodiversity of lichen biota. Microhabitat space provided by oaks is highly desirable since it greatly enriches lichen biota in forests. Phorophyte specificity of particular lichens were assessed. Hornbeam and oak have the greatest number of species mostly confined to them and constitute a main refuge for lichens with a high conservation value. The changes of lichen biota are basically parallel with the changes of the forest stand structure. The selection of some parts within managed pine forests that should not be assigned for cutting in the future can be a simple procedure which helps to restore and preserve forest biodiversity.     

Long‐term colonization ecology of forest‐dwelling species in a fragmented rural landscape – dispersal versus establishment

Species colonization in a new habitat patch is an efficiency indicator of biodiversity conservation. Colonization is a two‐step process of dispersal and establishment, characterized by the compatibility of plant traits with landscape structure and habitat conditions. Therefore, ecological trait profiling of specialist species is initially required to estimate the relative importance of colonization filters. Old planted parks best satisfy the criteria of a newly created and structurally matured habitat for forest‐dwelling plant species. We sampled species in 230 ancient deciduous forests (source habitat), 74 closed‐canopy manor parks (target habitats), 151 linear wooded habitats (landscape corridors), and 97 open habitats (isolating matrix) in Estonia. We defined two species groups of interest: forest (107 species) and corridor specialists (53 species). An extra group of open habitat specialists was extracted for trait scaling. Differing from expectations, forest specialists have high plasticity in reproduction mechanisms: smaller seeds, larger dispersules, complementary selfing ability, and diversity of dispersal vectors. Forest specialists are shorter, less nutrient‐demanding and mycorrhizal‐dependent, stress‐tolerant disturbance‐sensitive competitors, while corridor specialists are large‐seeded disturbance‐tolerant competitors. About 40% of species from local species pools have immigrated into parks. The historic forest area, establishment‐related traits, and stand quality enhance the colonization of forest specialists. The openness of landscape and mowing in the park facilitate corridor specialists. Species traits in parks vary between a forest and corridor specialist, except for earlier flowering and larger propagules. Forest species are not dispersal limited, but they continue to be limited by habitat properties even in the long term. Therefore, the shady parts of historic parks should be appreciated as important forest biodiversity‐enhancing landscape structures. The habitat quality of secondary stands can be improved by nurturing a heterogeneous shrub and tree layer, and modest herb layer management.     

Using forest history and spatial patterns to identify potential high conservation value forests in Romania

Naturally dynamic forests have a high proportion of biotopes with old large trees, diverse vertical and horizontal structure at multiple scales, and much dead wood. As such, they provide habitat to species and ecosystem processes that forests managed for wood production cannot provide to the same degree. Whether termed old-growth, ancient, virgin, intact, primeval or continuity forests, a major challenge and need is to map such potential high conservation value forest for subsequent inclusion in functional habitat networks for biodiversity conservation in forest landscapes. Given that the delivery time of natural forest properties is much longer than of industry wood, we explore the usefulness of using historical maps to identify forests that have been continuously present for 220 years (potential old-growth) versus 140 years (potential aging forest) in a case study in the Romanian Carpathian Mountains (see Online Resource 1). While the total forest cover increased by 35 % over the past two centuries, the area of potential aging and potential old-growth forest declined by 56 and 34 %, respectively. Spatial modelling of edge effects and patch size for virtual species with different requirements indicated an even greater decrease in the area of functional habitat networks of old-growth and ageing forest. Our analyses show that compared to simple mapping of potential high conservation forests, the area of functional habitat patches is severely overestimated, and caution is needed when estimating the area of potential high conservation value forests that form functional habitat networks, i.e. a green infrastructure. In addition, the landscape and regional scale connectivity of patches needs to be considered. We argue that the use of historical maps combined with assessment of spatial patterns is an effective tool for identifying and analyzing potential high conservation value forests in a landscape context.     

In search of the best local habitat drivers for saproxylic beetle diversity in temperate deciduous forests

Deadwood-associated species are increasingly targeted in forest biodiversity conservation. In order to improve structural biodiversity indicators and sustainable management guidelines, we need to elucidate ecological and anthropogenic drivers of saproxylic diversity. Herein we aim to disentangle the effects of local habitat attributes which presumably drive saproxylic beetle communities in temperate lowland deciduous forests. We collected data on saproxylic beetles in 104 oak and 49 beech stands in seven French lowland forests and used deadwood, microhabitat and stand features (large trees, openness) as predictor variables to describe local forest conditions. Deadwood diversity and stand openness were consistent key habitat features for species richness and composition in deciduous forests. Large downed deadwood volume was a significant predictor of beetle species richness in oak forests only. In addition, the density of cavity- and fungus-bearing trees had weak but significant effects. We recommend that forest managers favor the local diversification of deadwood types, especially the number of combinations of deadwood positions and tree species, the retention of large downed deadwood and microhabitat-bearing trees in order to maximize the saproxylic beetle diversity at the stand scale in deciduous forests. To improve our understanding of deadwood-biodiversity relationships, further research should be based on targeted surveys on species-microhabitat relationships and should investigate the role of landscape-scale deadwood resources and of historical gaps in continuity of key features availability at the local scale.     

Non-native plantation forests as alternative habitat for native forest beetles in a heavily modified landscape

The once extensive native forests of New Zealand’s central North Island are heavily fragmented, and the scattered remnants are now surrounded by a matrix of exotic pastoral grasslands and Pinus radiata plantation forests. The importance of these exotic habitats for native biodiversity is poorly understood. This study examines the utilisation of exotic plantation forests by native beetles in a heavily modified landscape. The diversity of selected beetle taxa was compared at multiple distances across edge gradients between each of the six possible combinations of adjacent pastoral, plantation, clearfell and native forest land-use types. Estimated species richness (Michaelis–Menten) was greater in production habitats than native forest; however this was largely due to the absence of exotic species in native forest. Beetle relative abundance was highest in clearfell-harvested areas, mainly due to colonisation by open-habitat, disturbance-adapted species. More importantly, though, of all the non-native habitats sampled, beetle species composition in mature P. radiata was most similar to native forest. Understanding the influence of key environmental factors and stand level management is important for enhancing biodiversity values within the landscape. Native habitat proximity was the most significant environmental correlate of beetle community composition, highlighting the importance of retaining native remnants within plantation landscapes. The proportion of exotic beetles was consistently low in mature plantation stands, however it increased in pasture sites at increasing distances from native forest. These results suggest that exotic plantation forests may provide important alternative habitat for native forest beetles in landscapes with a low proportion of native forest cover.     

Effect of Low Vegetation on the Recruitment of Plants in Successional Habitat Types1

I assessed the role of low vegetation (plants ca 1 yr old and ≤50 cm tall) as a biotic facilitator or barrier in the recruitment of different growth forms and species in primary forests, secondary forests, and old‐fields (abandoned pastures) in southeastern Mexico. I removed by hand all plants (≤100 cm tall, including roots) and litter from 20, 0.25 m² plots in each habitat. For 1 yr, I counted the number of plant species (5–50 cm tall) recruited, grouped them into different growth forms, and compared them to undisturbed control plots. Prior to manipulation, the standing density of trees and lianas was highest in primary and secondary forests. Shrubs were more abundant in secondary forests, whereas herbs, epiphytes, and hemi‐epiphytes were more abundant in old‐fields. Herbaceous plants appeared as important components of the community in all habitats. The removal of low vegetation increased total plant recruitment in all habitats. Considering each growth form, the absence of vegetation increased recruitment in primary forests for herbs, in secondary forests for epiphytes and hemi‐epiphytes, in old‐fields for trees, and for lianas in primary forests and old‐fields. In vegetation removal plots, recruitment of species was greater in pastures, lower in secondary forest, and similar in primary forest with respect to control plots. Depending on habitat type, species, and growth form, the presence of low vegetation may act as a recruitment barrier or facilitator for different species, affecting plant community structure, diversity, and composition in different habitats.     

Effects of Clearfell Harvesting on Lucanid Beetles (Coleoptera: Lucanidae) in Wet and Dry Sclerophyll Forests in Tasmania

The effects of commercial forestry harvest and regeneration practices (clearfelling and slash-burning) on the lucanid fauna of the wet sclerophyll forests of southern Tasmania and the dry sclerophyll forests of eastern Tasmania were examined using pitfall catches. Lucanids are saproxylic beetles, dependent on dead, moribund and decaying wood. Samples taken from old-growth forest and from a chronosequence of sites regenerating after logging, in each forest type, were used to compare the species richness and abundance of the lucanid assemblages. In both forest types, species richness and abundance was highest in the youngest regeneration sites (1–3 year), reflecting the species richness of the original and adjacent unlogged forest, lowest in the older (20–25 year) sites, and variable in the old-growth sites. TWINSPAN cluster analysis showed no clear distinction between regeneration and old-growth forest. The post-harvest slash and stump residue provided an important refugium and initial habitat, but our research indicates that some species may not maintain populations in the long term. Our results suggest that most species of lucanids will find a continuous supply of suitable habitat only in old-growth forests; and such species may become less common as clearfell harvesting leads to a replacement of heterogeneous old-growth forest with single-aged monospecific stands. Continuity of supply of wood in all decay stages, the maintenance of sufficient source areas, and biological connectivity between old-growth stands to enable dispersal, are all likely to be essential to maintain lucanid beetle community integrity. If similar principles apply to other saproxylic species of invertebrate, then clearfelling and slash-burning may cause a gradual extinction of an important element of the forest biota.     

林冠附生植物生态学研究进展

林冠附生植物及其枯死存留物是构成山地湿性森林生态系统中生物区系、结构和功能的重要组分。由于在林冠攀爬技术上的限制,过去对林冠附生植物在生态系统结构和功能过程中的作用未能引起足够的重视。近20年来,随着对林冠生物多样性及其在生态系统功能过程影响的认识和研究技术上的提高,对林冠附生生物的研究已逐步从个体水平转移到系统水平上。有关林冠附生植物多样性、生物量及其生态学效应已成为近年来国际上新兴研究领域——“林冠学”的研究热点之一。许多研究表明,林冠附生植物在生态系统水平上的交互作用比它们的解剖、形态和生理特征更为重要。国外大量的研究结果表明,林冠是一个适合于许多生物种类生存的场所,其数量比想象的更为丰富。在全球范围内估计有29 500余种附生植物,其中维管束附生植物的种类高达24 000种,约占总维管束植物种类的10%。林冠附生物的生物量在世界各地森林中存在较大的差异,其范围在105~44 000 kg·hm^-2之间,其中在一些热带和温带天然老龄林中林冠附生物的生物量超过了宿主林木的叶生物量。林冠附生植物还具有较大的叶面积指数(LAI)。林冠附生物丰富的物种组成、较高的生物量、独特的生理形态特征以及它们分布于森林与大气相互作用的关键界面,使得它们在生态系统物种多样性形成及其维持机制、养分和水分循环、指示环境质量等方面具有重要的作用。林冠附生植物及其枯死残留物具有较强的能力吸收雨水和空气中的营养物质,在林冠层中形成一个潮湿的环境促进氮固定,林冠附生植物群落还能为生存于林冠的其它生物(如鸟类、哺乳动物、两栖动物、爬行动物和昆虫等)提供食物和栖息场所。林冠附生植物的生长发育与分布格局除与宿主有关外,还受到环境因素(气候、地形、微生境条件等)和人为干扰的影响。由于世界各地森林类型多样和环境条件各异,目前国际上有关附生物的研究仍十分活跃,建立了林冠研究网络,研究不同类型森林中附生植物及其枯死残留物的动态及其与群落特征、环境因子的数量关系,探讨、交流和发展有效的标准测量方法和技术是该领域研究的主要内容。国内对林冠附生植物生态学的研究刚刚起步,有待于今后加强该领域的研究。     

Long-Term Impacts of Forest Ditching on Non-Aquatic Biodiversity: Conservation Perspectives for a Novel Ecosystem

Artificial drainage (ditching) is widely used to increase timber yield in northern forests. When the drainage systems are maintained, their environmental impacts are likely to accumulate over time and along accompanying management, notably after logging when new forest develops on decayed peat. Our study provides the first comprehensive documentation of long-term ditching impacts on terrestrial and arboreal biodiversity by comparing natural alder swamps and second-generation drained forests that have evolved from such swamps in Estonia. We explored species composition of four potentially drainage-sensitive taxonomic groups (vascular plants, bryophytes, lichens, and snails), abundance of species of conservation concern, and their relationships with stand structure in two-ha plots representing four management types (ranging from old growth to clearcut). We found that drainage affected plot-scale species richness only weakly but it profoundly changed assemblage composition. Bryophytes and lichens were the taxonomic groups that were most sensitive both to drainage and timber-harvesting; in closed stands they responded to changed microhabitat structure, notably impoverished tree diversity and dead-wood supply. As a result, natural old-growth plots were the most species-rich and hosted several specific species of conservation concern. Because the most influential structural changes are slow, drainage impacts may be long hidden. The results also indicated that even very old drained stands do not provide quality habitats for old-growth species of drier forest types. However, drained forests hosted many threatened species that were less site type specific, including early-successional vascular plants and snails on clearcuts and retention cuts, and bryophytes and lichens of successional and old forests. We conclude that three types of specific science-based management tools are needed to mitigate ditching effects on forest biodiversity: (i) silvicultural techniques to maintain stand structural complexity; (ii) context-dependent spatial analysis and planning of drained landscapes; and (iii) lists of focal species to monitor and guide ditching practices.     

Contrasting effects of habitat quantity and quality on moth communities in fragmented landscapes

Habitat loss is commonly identified as a major threat to the loss of global biodiversity. In this study, we expand on our previous work by addressing the question of how lepidopteran species richness and composition vary among remnants of North American eastern deciduous forest located within agricultural or pastoral landscapes. Specifically, we tested the relative roles of habitat quantity (measured as stand area and percent forest in the greater landscape) and habitat quality (measured as tree species diversity) as determinants of moth species richness. We sampled >19 000 individuals comprising 493 moth species from 21 forest sites in two forested ecoregions. In the unglaciated Western Allegheny Plateau, the species richness of moths with woody host plants diminished as forest stand size and percent forest in the landscape decreased, but the total species richness and abundance of moths were unaffected by stand size, percent forest in the landscape, or tree species diversity. In contrast, the overall species richness and abundance of moths in the glaciated North Central Tillplain were affected primarily by tree species diversity and secondarily by forest size. Higher tree species diversity may reduce species loss from smaller forest stands, suggesting that small, diverse forests can support comparable numbers of species to those in less diverse, large stands. Smaller forests, however, contained a disproportionate number of moth species that possess larvae known to feed on herbaceous vegetation. Thus, although woody plant feeding moths are lost from forests with changes in stand area, new species appear capable of recolonizing smaller fragments from the surrounding habitat matrix. Our study further suggests that when species replacement occurs, local patch size and habitat quality may be more important than landscape context in determining the community structure of forest Lepidoptera.     

The effects of forestry on carabid beetles (Coleoptera: Carabidae) in boreal forests

As compared to natural forests, managed boreal forests are younger, more homogeneous in terms of tree age and species composition, and consist of smaller fragments. Here we examine the effects of such characteristics caused by forestry on carabid beetles (Coleoptera, Carabidae) in the boreal region. The main results are the following. (1) Fragmentation of forests and the size of a fragment appear not to be crucial for the survival of the majority of forest carabids, as they tend to be distributed over various successional stages, but species requiring old-growth habitats suffer. (2) For carabids there appear to be no or very few edge specialist species, and forest-open land edges appear to be effective barriers for species associated with forest or open habitat. However, generalist species easily cross the edge, and edges of forest fragments may be invaded by species from the surrounding open habitat. (3) Habitat change following clear-cutting dramatically changes the composition of carabid assemblages: species restricted to mature forests disappear and open-habitat species invade, while habitat generalists survive at least in the short term. Carabid diversity can probably best be maintained if forest management mimics natural processes, maintains natural structures and includes the natural composition of vegetation and other structural elements (such as dead wood) within the stands, provided that these forest features can be maintained and recreated through forest management practices. At a larger scale, the whole spectrum of forest types and ages (especially old-growth forests), and different successional processes (especially fire) should be maintained. These require the development and use of innovative logging methods, and the planning, implementation, and assessment of landscape-scale ecological management strategies.     

Biodiversity conservation in old-growth boreal forest: black spruce and balsam fir snags harbour distinct assemblages of saproxylic beetles

Biodiversity conservation of forest ecosystems strongly relies on effective dead wood management. However, the responses of saproxylic communities to variations in dead wood characteristics remains poorly documented, a lack of knowledge that may impede the development of efficient management strategies. We established the relationship between saproxylic beetles—at the species and community levels—and attributes of black spruce and balsam fir in old-growth boreal forests. The relationship was first evaluated for individual snag bole segments, and then for forest stands. A total of 168 bole sections were collected in summer 2006 along a compositional gradient ranging from black spruce-dominated stands to balsam fir-dominated ones, in a boreal forest dominated by >90-year-old stands. A total of 16,804 beetles belonging to 47 species emerged from bole segments, with 21% of the species being found exclusively in black spruce snags and 36% exclusively in balsam fir snags. Black spruce and balsam fir snags thus contributed differently to forest biodiversity by being inhabited by different saproxylic communities. Wood density was an important attribute in the host-use patterns for several species of saproxylic beetles, but no relationship was found between snag availability within stands and abundance of beetles strongly linked to either black spruce or balsam fir. Our study outlines the relative contribution of tree compositional diversity to saproxylic species, while highlighting the contribution of black spruce and balsam fir to animal diversity in old-growth boreal forests.     

Separating forest continuity from tree age effects on plant diversity in the ground and epiphyte vegetation of a Central European mountain spruce forest

Forest continuity has been identified as an important factor influencing the structure and diversity of forest vegetation. Primary forests with centuries of continuity are usually more diverse than young secondary forests as forest are colonized only slowly and because the former are richer in old tree individuals. In the present study, performed in unmanaged high-elevation spruce forests of the Harz Mountains, Germany, we had the unique opportunity to separate the effects of forest continuity and tree age on plant diversity. We compared an old-growth spruce forest with century-long habitat continuity with an adjacent secondary spruce forest, which had naturally established on a former bog after 1796 when peat exploitation halted. Comparative analysis of the ground and epiphyte vegetation showed that the plant diversity of the old-growth forest was not higher than that of the secondary forest with a similar tree age of >200 years. Our results suggest that a period of >200 years was sufficient for the secondary forest to be colonized by the whole regional species pool of herbaceous and cryptogam forest plants and epiphytes. Therefore, it is likely that habitat structure, including the presence of old and decaying trees, was more important for determining plant diversity than the independent effect of forest continuity. Our results are probably not transferrable to spruce forests younger than 200 years and highly fragmented woodlands with long distances between new stands and old-growth forests that serve as diaspore sources. In addition, our results might be not transferable to remote areas without notable air pollution, as the epiphyte vegetation of the study area was influenced by SO₂ pollution in the second half of the 20th century.