Herbaceous species diversity, redundancy and resilience of Mopaneveld across different land-uses

Abstract

Savanna ecosystems are under increasing arthropogenic pressure. In semi-arid Mopaneveld, few studies have aimed to quantify and evaluate the extent to which anthropogenic disturbances affect plant diversity and function of the herbaceous layer. This study aimed to quantify the effect of various land-use practices on herbaceous plant community structure, which included productivity (biomass) as well as richness, evenness and diversity at species- and functional level. The objectives of this study were to i) determine to what extent land-uses affect species composition of herbaceous plant communities, ii) assess and compare land-use effects on species richness, evenness and diversity, iii) determine if land-uses adversely affects native species diversity, iv) quantify and compare response diversity of transformed and protected Mopaneveld, v) identify and describe plant functional groups of the herbaceous layer in Mopaneveld, vi) compare functional richness, evenness and diversity of traits and groups of each land-use and vii) relate observed species diversity and functional diversity patterns to habitat changes to facilitate comments regarding the level of resilience of anthropogenically disturbed Mopaneveld. The herbaceous layer of five land-uses was sampled using the fixed quadrat method. Eight plant traits were selected. PRIMER 6 software, Paleontological Statistics (PAST), STATISTICA version 11 and Canoco for Windows version 4.5 were used for data analyses, which included Non-metric Multidimensional Scaling (NMDS) ordinations, One-way Analysis of Similarities (ANOSIM), Similarity Percentage Analysis (SIMPER), non-parametric Analysis of Variance (Kruskal-Wallis ANOVA), One-way Analysis of Variance (ANOVA), Tukey’s post-hoc HSD (honestly significant difference) for unequal N, hierarchical cluster analyses, Principal Co-ordinate Analysis (PCoA) and several multivariate analyses. This study revealed that communal lands, strip mines and mine dumps have a filtering effect on species- and functional assemblages. Six unique plant functional groups, associated with life form, life history and weediness, were identified for anthropogenically disturbed Mopaneveld. Each land-use were characterised by distinctive trait sets and functional groups. Certain species with unique traits in a certain functional group fulfil important ecological roles in land-use plant communities. Species evenness was found to be sensitive to marginal disturbances and total transformation. Trait evenness was found to be sensitive to marginal disturbances. Low levels of species diversity were displayed by strip mined and mine dump plant communities. Dominant plant traits were considered to provide high trait-based redundancy and hence contributed to resilience of land-use plant communities. Response patterns of species diversity corresponds to response patterns of functional diversity for Mopaneveld, communal lands, strip mines as well as for Simpson diversity (on species-, trait- and group level) of koppies and mine dumps. Different response patterns were observed for Shannon-Wiener diversity on species-, trait- and group level of koppies and mine dumps. It is expecited that resilience can be considered high in Mopaneveld if species– and functional diversity is high. This study can be used as a framework for conservation actions and rehabilitation programmes in anthropogenically disturbed Mopaneveld. Inclusion of species and functional diversity provided valuable baseline information regarding redundancy and resilience. More studies are required to unravel long-term land-use effects in Mopaneveld to ensure the safeguarding of ecosystem resilience.