Edge effects at an induced forest-grassland boundary: Forest birds in the Ongoye Forest Reserve, KwaZulu-Natal

Abstract

Bird species diversity and guild composition between the edge (5-10 m from the margin) of primary forest abutting grassland and the deep interior (> 500 m from the margin) in the Ongoye Forest Reserve were compared. Edge and interior sites were chosen that were homogeneous with respect to habitat physiognomy i.e. influences of habitat structure and complexity were insignificant. There were no statistical differences in bird species diversity between the forest edge and interior. However, there was significantly greater species turnover at the edge. The difference in bird species composition between the forest edge and interior was due to various edge-effects: removal of dead wood for firewood, soil compaction by cattle, and generally greater levels of disturbance. We question the wisdom of the generally applied edge-effect principle in the conservation of forest biodiversity. We suggest that the principle be applied only once there has been critical appraisal of the extent, nature, and effect of an edge and a clear conservation objective with regard to forest birds.