Do ecological networks in South African commercial forests benefit grassland birds? A case study of a pine plantation in KwaZulu-Natal

Abstract

Grasslands in South Africa have been extensively transformed and fragmented, but are poorly protected. Commercial afforestation poses a particular threat to grassland biodiversity because areas suitable for forestry coincide with those supporting the greatest richness of endemic and threatened biota. To comply with international forestry standards, commercial timber growers leave “ecological networks” of interconnected open corridors within plantations: however, the value of these networks for conservation is unclear. This study investigated how bird community composition, richness and density were influenced by habitat extent, connectivity and quality in a grassland ecological network in a forestry plantation in KwaZulu-Natal, South Africa. We surveyed birds and measured local vegetation characteristics throughout the network. There were at least five open habitat types within the network and bird communities responded clearly to differences between these habitats: all network communities showed a distinct shift away from those typical of control grasslands. There were three distinct groups of species in the network: (1) grassland specialists, (2) habitat generalists and (3) non-grassland species. Grassland specialists were restricted to areas that are burned regularly and to large, contiguous open areas or wide grassland corridors. We found no evidence for the importance of physical connectivity among open habitats for birds in the study area. Instead, it appears that the establishment of so-called ecological networks at this scale has created much unsuitable habitat for grassland specialist species. We suggest consolidation of open areas and a rotational, biennial burning regime as a more appropriate management strategy for commercial plantations in these Critically Endangered montane grasslands.