Response of arthropod biodiversity to native vegetation and monoculture plantations: implications for conservation and management.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.

Timber plantations are valuable to the global economy. They are inevitably forming part of future landscapes as they have become one of the main land use occupying the global land area. There is a growing interest and debate on their effect on biodiversity since they are non-native habitats with conservation potential. However, biodiversity response to timber plantations remains ambiguous, as previous studies have reported mixed findings. In addition, the factors that drive species’ taxonomic responses to disturbance are not well-studied. Given that invertebrates, particularly arthropods, are the most abundant, the current study will investigate their response to timber plantations (at a global scale) and their diversity and drivers at a local scale (in the Midlands of KwaZulu-Natal). Particularly, the current study aimed to 1) systematically review published literature on arthropod diversity patterns in Pinus and Eucalyptus timber plantations versus natural vegetation globally, 2) compare the diversity and assemblage composition of different arthropod taxa in these plantations and a native forest in South Africa, 3) determine the environmental factors that drive such patterns, and 4) Assess the functional composition of arthropods in these habitats. To determine the response of arthropods to timber plantations globally, PRISMA guidelines were followed to systematically review the literature. One hundred and eleven studies from 30 countries were selected from the Web of Science, Google Scholar, and Scopus. The review highlighted that arthropod diversity declines with increased habitat simplicity, an attribute of most commercialised timber plantations of tree species outside their native ranges. To assess arthropod diversity at a local scale, ground-dwelling arthropods were collected using pitfall traps from Pinus and Eucalyptus plantations and a native forest in the Natal Midlands. Environmental data were recorded to test whether arthropods were driven by forest type, season, or microhabitat variables within those habitats. A total of 4 284 arthropod individuals were collected. Although different arthropod taxa had unique responses, the overall arthropod diversity was fairly similar across the three habitats. Habitat heterogeneity was higher in the native forest and correlated with the species richness of beetles and myriapods (centipedes and millipedes). Spider species richness was mainly driven by season, with most spider species collected during the dry-hot season. Ants were best predicted by habitat type as more species were collected in the native forest, although this was not statistically significant. The assemblage composition of beetle and spider communities significantly differed across the habitats, while ants and myriapods had similar communities. Functional redundancy was evident across the site, implying that declines in species richness in the plantations did not lead to a loss of ecosystem functions. This study shows that the generalisation of biodiversity response to timber plantations may be misleading. Rather, future studies should focus on the habitat-specific elements that drive species distribution in these disturbed ecosystems. In addition, it highlights the need to use complementary facets for biodiversity assessment, as taxonomic diversity may provide limited information on ecosystem functions if not combined with functional diversity.