Effects of surrounding landscape composition on the conservation value of native and exotic habitats for native forest birds

The contribution of different production land uses to the conservation of native forest birds in modified, fragmented landscapes is a question of increasing relevance worldwide. Here, we tested the hypothesis that the abundance of native forest birds increases with increasing area of exotic plantation forests surrounding native forest remnants due to a reduction of negative effects of forest fragmentation and the provision of additional habitat. Conversely, farmland was not expected to provide such benefits to the same extent. Nine species of native birds were sampled in 238 plots in native forests, exotic plantation forests and mixed farmland on Banks Peninsula, South Island, New Zealand, where these land cover types are highly interspersed in a variety of spatial configurations. Around each sampling plot we determined the cover of native forest, plantation forest and mixed farmland within seven buffer zones ranging in radius from 200 m to 3000 m, using the New Zealand Land Cover Database 2. In native forests, the abundance of all but one species was negatively correlated with the amount of farmland surrounding points whereas the opposite applied when points were surrounded by native forest. There was a variable effect for native forest surrounded by plantation forest. In exotic plantation forests and farmland, the abundance of most species was positively correlated with the amount of native forest surrounding points. By contrast, for most species there was a small or moderate negative correlation with surrounding plantation forest. In farmland plots, bird abundance was positively correlated with native forest cover whereas plantation forest and farmland cover negatively affected most species. These results suggest that exotic plantation forests may mitigate effects of forest fragmentation for some native forest birds but not for others, and this appeared to depend on the landscape context. The maintenance of native forest remnants and forest restoration across the landscape, including within production land areas are important for the long-term conservation of the New Zealand's forest avifauna.