Ecological networks act as extensions of protected areas for arthropod biodiversity conservation.
Abstract
Landscape-scale ecological networks (ENs) are composed of linear corridors and are widely used to mitigate the adverse effects of intensive land use. One drawback with ENs used for conservation is that being small or linear they result in more edge relative to interior than would be the case naturally. Furthermore, there is little evidence to date that ENs do conserve indigenous biodiversity. Here, we use five arthropod taxa at many sites over two geographical areas within South Africa with different elevations and grassland types to test the conservation value of remnant grassland ENs in a plantation forestry context. In particular, the relative value of arthropod biodiversity in exotic plantation blocks, their edges and the interiors of ENs among the plantations were compared with those in neighbouring protected areas (PAs). We use the effects that the plantation blocks have on the adjacent PAs as a reference for comparing the ENs among the plantations. Arthropods were selected to represent biodiversity, as they are small, diverse, habitat sensitive, resource dependent, ecologically important and can be sampled in large numbers. In total, 10 422 individuals from 244 species were sampled. Importantly, there were no significant differences in species richness, abundance or assemblage composition between EN interior zones and PA interior zones in both geographical areas. Using earlier established edge zones of 32 m, we found that plantation blocks had the lowest species richness and abundance compared with either grassland edge zones (<32 m from the edge) or grassland interior zones (≥32 m from the edge). Synthesis and applications. Ecological networks are established to conserve biodiversity in areas of intensive land use. Provided that ecological networks are wide enough (i.e. >64 m) to overcome edge effects, they can support similar levels and quality of arthropod biodiversity as protected areas. Remnant grassland ecological networks in agroforestry can provide natural finger-like extensions from neighbouring protected areas and therefore have conservation value.