Consequences for bird diversity from a decrease in a foundation species—replacing Scots pine stands with Norway spruce in southern Sweden

Abstract

Forest ecosystems are often defined by their dominant foundation tree species, which dictate forest structure and ecosystem processes. In southern Sweden, concerns are being raised because production stands of a foundation tree species, Scots pine (Pinus sylvestris), are being converted to Norway spruce (Picea abies) stands. Such conversions may lead to biodiversity loss, though the specific nature and extent of such losses remain unknown. Here, we assess the potential biodiversity impacts by contrasting the bird communities of 55- and 80-year-old Scots pine and Norway spruce production stands. We also determine the extent to which these production stands capture the available species pool by surveying conifer-dominated reserves. Our results indicate that Scots pine and Norway spruce production forests support overlapping but nevertheless distinct bird communities, though only few recordings were made of the species unique to either stand type. Among the production stands, the 80-year spruce stands had the highest average bird species richness, and largest total number of species recorded. We suggest that the higher diversity can be explained by a higher proportion of broadleaves and higher volumes of dead wood. Although the bird diversity found in the reserves was lower than expected, they benefit gamma diversity at landscape scales as they collectively supported a higher diversity of bird species than the production forests. In summary, the conversion of Scots pine to Norway spruce is likely to increase the homogeneity of the bird communities in this region.