Long-term decline of southern boreal forest birds: consequence of habitat alteration or climate change?

Climate change and habitat degradation due to land use are the key factors threatening biodiversity. It is important to study both the separate and joined effects of climate warming and land use on biodiversity. In this work long-term population changes of southern boreal forest birds were studied in relation to climate change and direct habitat alteration due to forestry. The study was based on annually repeated bird censuses in 23 consecutive years (1993-2015) in a managed forest landscape. Results were compared with population changes in protected areas where logging is not allowed. During the study period, total bird density declined by 18 % with a change in the bird community composition. Out of the 12 most abundant species seven showed a significant negative trend and only one species a positive trend. Population declines could be connected with the direct alteration of habitat as a consequence of forestry or with the effect of climate change in the case of those species which declined also in protected areas. The increased species are abundant across Europe in human-modified habitats. Due to habitat alteration and climate warming, specific characteristics of southern boreal forest bird communities are changing with communities representing a pattern towards global homogenization. Thus, habitat alteration strengthens the negative effects of climate change.