Tree-related microhabitats on live Populus tremula and Picea abies in relation to tree age,diameter, and stand factors in Estonia     

Kõrkjas  Maarja  Remm  Liina  Lõhmus  Asko 《European Journal of Forest Research》2021,140(5):1227-1241

Production forestry is known to reduce the naturally variable microhabitat pools in live trees and their biodiversity by tree removal and broad indirect effects of silviculture. However, the tree-scale processes are not known well enough for microhabitat management for the future. This study investigates how tree age affects the microhabitat occurrence in live trees, its effect modifiers, and explanatory value compared with tree diameter. We inventoried tree-related microhabitats on 879 live aspens (Populus tremula) and Norway spruces (Picea abies) of known age in 141 forests representing contrasting productive site conditions in Estonia. We analysed microhabitat incidence using logistic mixed models for significant tree-scale and stand-scale factors. Most microhabitat types appeared rare even in old trees, and the age effects had various patterns. Only 2% of trees bore five or more microhabitat types. Aspens and spruces had a similar microhabitat diversity before 80 years of age. Stand-level effects varied among microhabitat types but were less significant than tree-level effects; interactions were even rarer. Most effects found could be interpreted through known ecological processes; for example, humidity-dependent epiphytic growth; bark stripping by herbivores; pathogen effects in forests with distinct histories. In contrast, a reliable tree-scale prediction of microhabitat occurrence appears rarely possible; and depending on microhabitat type, either tree age or diameter can be a better predictor. We suggest that managing for tree-related microhabitats in production forests should combine facilitating ecological conditions for microhabitat formation, and early detection and retention of the trees with high microhabitat potential.

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Bird communities in hemiboreal old-growth forests: The roles of food supply, stand structure, and site type     

Raul Rosenvald  Asko LõhmusAnn Kraut  Liina Remm 《Forest Ecology and Management》2011,262(8):1541-1550

Key factors causing the difference of wildlife populations in natural and managed forests are an important field of ecosystem and biodiversity research. To explore the factors contributing to bird-community features in the poorly studied European natural hemiboreal forests, we carried out a comparative study in old-growth and mature stands of five site types in Estonia. The mature stands were of clear-cut origin and managed for timber production. Old-growth hosted both more diverse and more abundant bird communities than mature stands, which does not support the putative ‘old-growth syndrome’ (high diversity at a low density) described previously in temperate Europe. Site-type specificity of bird communities was also more pronounced in old-growth, indicating a timber-harvesting induced process of biotic homogenization. In particular, natural swamp forests had characteristic bird species and those communities may be additionally sensitive to artificial drainage. In terms of invertebrate food supply, the availability of snails, rather than of insects, was related to bird-community characteristics; however, the influence of snails was due to one snail-poor forest type (Vaccinium type pine stands), not management. The abundance of coarse woody debris was the main structural feature affecting bird communities; tree-size variation was additionally important for species richness. A significant unexplained ‘old-growth’ effect remained even after the variables describing food supply and stand structure were taken into account. Our results imply the distinct importance of old-growth of different site types for hemiboreal bird communities. However, we did not obtain any evidence of different key factors structuring the bird communities in old-growth and mature stands.  相似文献