The diversity and distribution of topsoil and leaf litter arthropods in timber plantation landscape mosaics

[摘要] ENGLISH ABSTRACT: Landscape planning for conservation is of great importance in high-impact production systems, such as commercial timber plantations. Ecological networks (ENs) have been applied on a large scale in exotic timber plantations in South Africa to mitigate the impacts of forestry by connecting remnant natural areas of high conservation value across the landscape. Natural remnants, such as Afromontane forests and grasslands have received much conservation attention within these ENs, yet the value of conserving grassland on hydromorphic soils remains poorly understood. We also still have limited information on arthropods occurring in the topsoil and leaf litter layer, despite their great functional importance, especially in hydromorphic grasslands. The removal of pine trees from these hydromorphic grasslands is a conservation measure to restore hydrological function within plantation landscapes. However, the effectiveness of restoration for biodiversity has not yet been determined.The study was conducted in the KwaZulu-Natal Midlands. The diversity and distribution of topsoil and leaf litter arthropods within four dominant biotopes (Afromontane forests, pine plantations, dry grasslands and hydromorphic grasslands) was determined. The biodiversity of hydromorphic grasslands was compared to the other biotopes occurring within an EN-plantation landscape mosaic. In addition, to determining whether restoration leads to successful recovery of the arthropod fauna after the removal of pine trees from hydromorphic grasslands, I compared the diversity of topsoil and leaf litter arthropods between natural untransformed hydromorphic grasslands, restored hydromorphic grasslands and pine plantations.All the natural untransformed biotopes (i.e. natural forest, dry and hydromorphic grassland) had higher arthropod species diversity compared to the transformed biotope (i.e. pine plantation). Hydromorphic grasslands differed significantly from the other dominant biotopes regarding arthropod assemblage structure, but not in terms of species richness. Thus, hydromorphic grasslands are unique landscape elements that complement the other untransformed biotopes, and contribute to landscape heterogeneity and overall biodiversity within the production landscape. Although hydromorphic and dry grasslands are classified as one vegetation type, I found that here, they were two distinct biotopes, both of which should be conserved separately owing to their unique arthropod assemblages.After the removal of pine trees from hydromorphic grasslands, the diversity and assemblages of topsoil and leaf litter arthropods have the capacity to recover to levels similar to that of natural hydromorphic grassland. However, contrary to what was expected, the assemblage similarity between the restored and natural hydromorphic grasslands was significantly negatively correlated to time since pine removal. American bramble (Rubus cuneifolius), which was more prevalent in older post-restoration sites, had the most significant negative effect on the assemblage similarity between the restored and natural hydromorphic grasslands, causing some restored sites to deviate from the restoration trajectory. Therefore, successful restoration of these hydromorphic grasslands to near natural conditions requires supplementary management inputs through removal and management of R. cuneifolius as a key management priority.

[发布机构] Stellenbosch University