Characterising the richness and diversity of forest bird species using National Forest Inventory data in Germany

Abstract

Data collected by forest inventories like the third National Forest Inventory (NFI-3, 2011–2012) in Germany was proposed to monitor forest biodiversity and evaluate existing forest management practices on a national scale. A data set was created from the NFI-3 data for analysis purposes which contained variables relevant to the habitat requirements of native forest bird species. Information on the distribution and abundance of 20 native forest bird species was taken from the Atlas of German Breeding Birds (2005–2009, 3003 grid cells). They form two important ecological groups: cavity-nesting and deciduous forest birds. For the first time, this data was combined with NFI-3 data and analysed using Random Forest models and partial dependence plots to determine which forest variables recorded by the NFI-3 were most closely related to forest bird species richness and diversity in temperate forests.It was shown that changes in forest bird species diversity and richness correlate with the NFI data but the different sampling methods of the NFI and bird species data also created methodological challenges which are discussed. The most important drivers of the richness and diversity of deciduous forest and cavity-nesting bird species are forest stand age and forest ownership. Deciduous forest and cavity-nesting birds show a preference for the way state, federal and municipal forests are managed over private forests. Private forests have significantly lower deadwood volumes and high proportions of coniferous trees, both of which are forest characteristics that lower the richness and diversity of bird species. Our findings show that efforts to protect forest birds should target managed forests older than 100 and 200 years and forests with total deadwood volumes >46.3 m3/ha. Protected areas also exhibited higher diversity and richness of forest birds which highlight their importance as suitable target areas for the protection of forest birds.