| Yhteenveto: | Forest management practices have remarkably intensified over the past century in Finland. The predominant management practice is clearcutting followed by tree planting, which results in homogeneous and younger forest habitats. These local modifications affect biodiversity negatively as crucial resources are being removed. However, the landscape-level and long-term impacts of clearcutting are still unclear because large-scale time series data are scarce. This thesis investigated how the accumulation of clearcutting over time and space, and their average size affects different bird communities, whether open-habitat species benefit from clearcutting and for how long, and if there is a threshold defining a maximum viable clearcut area in a landscape. Using data from the Finnish bird monitoring transects and the European disturbance map describing clearcuts, the effects of clearcut accumulation were inferred over different spatial and temporal scales on species richness and abundance of different bird functional groups within forested landscapes of Southern Finland. The impacts were estimated using generalized linear mixed models (GLMM) and regression trees. Habitat heterogeneity positively affects overall bird species richness, especially through smaller clearcuts (edge habitats). Clearcuts affect forest birds negatively and especially old-growth forest species experience negative effects from the 20-year accumulation of clearcuts, with threshold level at 20% area of a landscape for them. Open habitat birds respond positively to clearcuts at 20-year time scales, therefore still benefitting from clearcut at longer time period. Additionally, species group responses vary in different spatial and temporal scales. Some birds benefit from short-term and localized effects, but large and long-term effects and excessive forest cover can negatively impact others. Observed threshold level and the average proportion of clearcuts imply unsustainability of current forest management practices in Finland.
|
|---|