Effects of habitat heterogeneity on bird communities in forests of northeastern Germany

Habitat heterogeneity is a key factor for regulating biodiversity in temperate lowland forests. Specifically, stands associated with late forest development phases provide important habitat structures for many rare and threatened forest bird species. However, how forest stands that differ in their structural complexity, canopy conditions and tree species composition affect forest bird assemblages both at the local and landscape scale remains largely unclear. In a young moraine lake landscape of northeastern Germany, we assessed correlations of bird diversity and bird composition with stand properties. We used data from 48 transects (400 m) established in (1) unmanaged, closed-canopy, mature stands that were dominated by Fagus sylvatica (UDS), and (2) diverse managed, mixed coniferous stands with a mosaic of open and closed canopy patches (MCS). We found that bird communities of the UDS strongly differed from those in the MCS, with open habitat species being more frequent in the MCS. By contrast, differences in diversity measures were less distinct. Moreover, we identified nine indicator species for the UDS (Columba oenas, Cyanistes caeruleus, Muscicapa striata, Leiopicus medius, Certhia brachydactyla, Ficedula parva, Dryobates minor, Sturnus vulgaris, Ficedula hypoleuca) and seven indicator species for the MCS (Periparus ater, Pyrrhula pyrrhula, Regulus regulus, Prunella modularis, Lophophanus cristatus, Emberiza citronella, Anthus trivialis). Several famous ancient beech forest patches in Muritz National Park and the UNESCO Biosphere Reserve "Schorfheide-Chorin" were found to harbour the set of our UDS indicator species. UDS support bird coenosis typical for old mature broadleaved forests and can be considered as an effective tool for bird conservation. Our results further indicate that the combination of unmanaged and managed stands associated with different habitat complexities would benefit forest bird assemblages at the landscape scale.