Habitat composition and bird diversity in managed boreal forests

This study investigated the occurrence of 25 forest bird species in relation to stand and landscape habitat composition in managed boreal forests in central Sweden. The number of species in 10 km transects was positively correlated to the proportions of forest > 40 yrs and Mixed forest > 40 yrs, as well as the number of fragments of the latter, while negatively correlated to the proportions of clear-cuts and young forest. Transects with > 60% older forest including > 6% mixed habitats showed the highest number of bird species and individuals. The positive effect on species numbers of mixed forest was stronger in the study area where deciduous rich habitats were generally less abundant. Bird species richness in points of similar habitat was negatively correlated to the degree of fragmentation of the surrounding older forest. However, in a species-by-species analysis at the transect level no effects of fragmentation were found. The number of bird species at points was positively influenced by the increase from 0 to 5% deciduous trees, while no effect of higher deciduous site proportions showed. The hazel grouse (Bonasa bonasia) appeared as a significant indicator of high bird diversity at the transect ( landscape) level, by all methods used. However, the conclusion was reached that forests where the hazel grouse, blue tit (Parus caeruleus), treecreeper (Certia familiaris), jay (Garrulus glandarius) and capercaillie (Tetrao urogallus) are present are most likely to hold the potential for high bird species richness.