Component Of Forest Biodiversity Research Articles

Influence of individual tree characteristics, spatial structure and logging history on tree-related microhabitat occurrence in North American hardwood forests

BackgroundTree-related microhabitats (hereafter, “TreMs”) are key components of forest biodiversity but they are still poorly known in North American hardwood forests. The spatial patterns of living trees bearing TreMs (hereafter, “TreM-trees”) also remain to be determined. As logging practices can lead to a loss of TreM-trees and of their associated biodiversity, it is essential to identify the factors explaining TreM occurrence to better integrate them into forest management. We therefore inventoried TreMs in 4 0.5-ha survey strips in northern hardwood forests in Quebec, Canada, while recording the spatial location of each tree. Two strips were located in unmanaged old-growth forests, and 2 were in forests managed under selection cutting. All 4 stands were dominated by sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrn.). Beech bark disease, an exotic pathology, was observed in all the strips.ResultsLarge diameter at breast height and low tree vigor were the main characteristics explaining the presence of TreMs at the tree scale. TreM-trees presented slight spatial aggregation patterns. These aggregates, however, were not well-defined and were generally constituted by a large number of trees bearing few different types of TreMs. Two TreM classes (broken branch or top and woodpecker lodge) also presented a spatial aggregation. Logging practices had no significant effect on TreM occurrence. Beech bark disease increased the frequency of senescent beeches. The impact of this pathology on TreMs was however mitigated by the small size of infected trees and probably by the short time elapsed since its appearance.ConclusionThe factors explaining the presence and abundance of TreMs on trees has so far been little studied in North American hardwood forests. Our results highlight that TreM-tree characteristics in the surveyed forests are consistent with those of previous studies conducted in other forest types and regions (e.g., Europe or Northwestern America). To our knowledge, this study is also the first to identify a spatial aggregation of TreM-trees and of specific TreM classes. It will be nevertheless necessary to determine whether the small impact of logging activities we observed results from current or past management practices.

Biodiversity response to forest management intensity, carbon stocks and net primary production in temperate montane forests

Managed forests are a key component of strategies aimed at tackling the climate and biodiversity crises. Tapping this potential requires a better understanding of the complex, simultaneous effects of forest management on biodiversity, carbon stocks and productivity. Here, we used data of 135 one-hectare plots from southwestern Germany to disentangle the relative influence of gradients of management intensity, carbon stocks and forest productivity on different components of forest biodiversity (birds, bats, insects, plants) and tree-related microhabitats. We tested whether the composition of taxonomic groups varies gradually or abruptly along these gradients. The richness of taxonomic groups was rather insensitive to management intensity, carbon stocks and forest productivity. Despite the low explanatory power of the main predictor variables, forest management had the greatest relative influence on richness of insects and tree-related microhabitats, while carbon stocks influenced richness of bats, birds, vascular plants and pooled taxa. Species composition changed relatively abruptly along the management intensity gradient, while changes along carbon and productivity gradients were more gradual. We conclude that moderate increases in forest management intensity and carbon stocks, within the range of variation observed in our study system, might be compatible with biodiversity and climate mitigation objectives in managed forests.

Salvage logging reduces wild bee diversity, but not abundance, in severely burned mixed-conifer forest

Natural disturbances are critical for supporting biodiversity in many ecosystems, but subsequent management actions can influence the quality of habitat that follow these events. Post-disturbance salvage logging has negative consequences on certain components of forest biodiversity, but populations of some early seral-adapted organisms may be maintained in salvage-logged areas. We investigated the influence of an essential group of pollinators – wild bees – to recent post-wildfire salvage logging within managed mixed-conifer forest in the Pacific Northwest. We compared bee diversity (i.e., bee abundance, species richness, alpha diversity, and beta diversity) and habitat features (i.e., floral resources and available nesting substrates) in salvage-logged areas to unlogged sites, both of which experienced high-severity wildfire. Although we found no evidence for differences in bee abundance between salvage-logged and unlogged sites, interpolated estimates of species richness and both interpolated and extrapolated estimates of alpha diversity were greater in unlogged sites. Additionally, beta diversity was greater in unlogged sites when equal weight was given to rare species. Salvage logging did not select for specific functional groups of bees, as both logged and unlogged sites were dominated by generalist, social species that nest in the ground. However, habitat conditions for bees were influenced by salvage logging: flowering plant density was greater in salvage-logged sites during the latter half of the season, with fewer conifer snags and more woody debris than were available in unlogged sites. Our study indicates that salvage logging can support wild bee abundance, but that unlogged patches of severely burned forest supports slightly greater bee diversity within fire-prone mixed-conifer landscapes.

A simple multivariate analysis to assess diversity in a complex long-term managed forest area in central Italy

Today wood and nonwood forest resources management meets and often clashes with environment and biological diversity protection. A main problem is to understand relationships between the different roles of forest biodiversity, site, and management parameters. A multivariate statistical analysis has been carried out in order to interpret relationships between some forest biodiversity components and forest inventory data. Several indices of floristic diversity, species abundance, and structural heterogeneity at stand level have been calculated. The different components of forest biodiversity were separated by principal components analysis. Relations between forest biodiversity indices and site and management attributes have been investigated by two multivariate statistical techniques: bivariate correlation analysis and multiple linear regression. Results showed a high correlation between all the investigated components of forest biodiversity and some topographic and/or forest management attributes. Results also gave ancillary information to define sustainable forest management criteria.

Importance for forest plant communities of refuges protecting from deer browsing

There is growing evidence that the increase of wild ungulates worldwide is responsible of strong deleterious impacts on various component of forest biodiversity (tree and shrub regeneration, insects, songbirds). Plant communities are particularly affected by overbrowsing, and overabundant deer are increasingly recognized as a major factor of decline in understory plant diversity in temperate and boreal forest ecosystems.In grassland ecosystems, refuges from herbivores have been shown to provide suitable habitat for plants sensitive to browsing and grazing, and to allow the conservation of rare plant species. In the present study we analyze if such refuges can maintain representative samples of forest plant communities exposed to strong browsing pressure by deer. For this we used the unique situation offered by the presence, side by side, on the Haida Gwaii archipelago of forested islands colonized or not by introduced deer.We compared plant assemblages on rocky outcrop to assemblages found in the adjacent field-layer in order (1) to assess, on islands without deer, the potential of refuges to be representative of the local field-layer communities and (2), on islands colonized by deer for over 60years, to analyze how far plant assemblages on rocky outcrops are representative of un-browsed field-layer communities and can serve as bioassays for field-layer plant communities in the absence of unbrowsed reference sites. We did this for forest-interior field-layer plant communities as well as for the forest edge plant communities found along the shorelines. We used refuges on treefall mounds to assess the role refuges can play as sources of propagules in two understory shrubs and ferns.Our results indicate that, in presence of deer, plant species density and plant cover are dramatically higher in refuges than in the adjacent field-layer plots. The comparison of these refuge communities to the reference state provided by the field-layer on islands without deer indicated that refuges maintain a representative part of the unbrowsed plant community, although with differences in the cover percentage in some plants. Some typical plants are more abundant in the refuges and, more sobering, six field-layer species are only poorly present in the rocky habitat. Despite these differences and their small size, refuges shelter a representative part of the understory and forest edge vegetation of the studied sites and could serve as a bioassay of deer overbrowsing in situations lacking a reference state.

Intensification des prélèvements de biomasse et préservation de la biodiversité forestière

After describing peculiarities and stakes in forest biodiversity, we discuss the response of biodiversity to potential habitat changes induced by increasing forest biomass harvesting: decrease in old trees and stands, and in forest areas unmanaged for decades, increase in overall felled areas, in forest road density and in habitat fragmentation, deleterious changes in soil conditions and forest ambiance, development of short and very short rotation coppices. Positive or negative effects on several components of forest biodiversity (mainly soil fauna and flora, and dead wood associated species) are explored. Needs are highlighted: biodiversity monitoring, adaptive management and context-based recommendations.