Population trends of common breeding forest birds in southern Finland are consistent with trends in forest management and climate change

Abstract

In Finland, modern forestry has caused the gross modification of native forest habitats and a loss of biological diversity due to intensive management regimes. Although less than 1% of the old-growth forest area remains in southern Finland, the effects of forestry on bird population long-term trends have not been comprehensively studied in this area. To fill this knowledge gap, we analysed 30 years of monitoring data of 32 common forest breeders in southern Finland. For each species, we fitted piecewise log-linear trends in two segments: 1984–1998 (period 1) and 1999–2013 (period 2). The estimated trends were analysed in relation to the species-specific habitat preferences, average tree height preference, migratory strategy, and latitudinal distribution. The trends turned on average more negative in period 2 compared to period 1, but the between-species variation in this change was not explained by any of the predictors. For the whole study period, species with a preference for late successional and nutrient-poor habitats (mostly found in northern latitudes) showed more negative population trends. In addition, trends changed on average –3%/ 500 km latitude.We further developed three summarizing multi-species indices, most of which should be useful for monitoring the general state of breeding forest bird communities in southern Finland. Our results suggest that bird communities are shaped by both a loss of mature forests and by climate warming. The decline of birds preferring native forests, reflected by the mature forest index, could undoubtedly change with an improvement of the conservation effectiveness in southern Finland.