Epsilon Archive for Student Projects

Abstract

Due to climate change mitigation, the need for wood for energy production is increasing. In response, fast-growing broadleaves, among them silver birch (Betula pendula), hybrid aspen (Populus tremula × P. tremuloides) and poplar (e.g. Populus trichocarpa × P. maximowiczii (OP42)) are being planted mainly on former agricultural land as short-rotation plantations. Since these plantations are sometimes treated as agricultural land, the silvicultural measures are different compared to normal production forest systems. Furthermore, of these tree species, only birch is considered native to Sweden. Differences in the homogeneity of stand structure, and variation in the use of native, hybrid and non-native tree species, could cause differences in bird community composition and abundance. These differences could be of relevance to forest biodiversity outcomes.
This study analysed the difference in bird diversity, considering species richness and abundance, between the three aforementioned tree species. Furthermore, the study investigated the extent of influence on bird diversity from stand characteristics: stand size, basal area, quadratic mean diameter, understory vegetation, and dead wood volume. I surveyed 18 fast-growing broadleaf stands located in Skåne; first the vegetation was measured, and second, bird data was collected in the early spring. For the bird data I conducted point count surveys in all three stand types, with results restricted to individuals showing territorial behaviour (singing, nesting behaviour).
A total of 29 bird species and 333 individual birds were detected, four of which are listed as near-threatened, and one as endangered according to the Swedish Red List. Most species encountered were habitat generalists and residents. The highest bird species richness and bird abundance were counted in birch stands, followed by hybrid aspen, and then poplar stands, within which I counted the lowest bird species richness and abundance. The highest species richness among broadleaf-associated species and migrants was found within hybrid aspen stands. My results indicate that tree species and basal area had an impact on bird diversity. For the other vegetation measures, no significant effect on the bird composition was found. Nevertheless, these measures gave insights into stand structure, which showed a greater heterogeneity in the exotic tree species than expected and therefore, can explain the relatively high bird diversity in hybrid aspen plantations. This result also suggests that further research is needed to test the influence of vegetation measures on bird diversity in fast-growing plantations. Additionally, a potential effect of the surrounding landscape was found, indicating that further research is needed to understand how surrounding environmental conditions may influence bird composition in the surveyed stands.
All of these findings have implications for our understanding of how tree species choice and the management of short-rotation plantations of fast-growing broadleaves can alter bird diversity and abundance.