Tree biomass carbon stocks and biodiversity, and their determinants in a traditional agroforestry landscape in the Vhembe Biosphere Reserve, South Africa

Abstract

Traditional agroforestry systems have been recognized worldwide for their positive contribution to biodiversity conservation, climate change mitigation, and improving socio-economic livelihood. Little has been reported regarding the effects of ecological determinants (tree density, species richness and diversity) on the biomass carbon accumulation potential of traditional agroforestry in South Africa, especially in the Vhembe Biosphere Reserve (VBR). The main objective of this study was to quantify tree biomass carbon stock and biodiversity in the VBR traditional agroforestry landscape along three distance levels (immediate, intermediate, and far distance) from villages to the forest. Vegetation data was collected using forestry inventory tools. In each distance, nine (9) linear transects (250 m long) were established with five rectangular plots (20 × 10m2) in 10 m apart. The sampling intensity was 10% and the sampling effort achieved was > 80%. Tree diversity metrics and above-and below ground carbon estimates were calculated from the data and then analyzed using PERMANOVA, ANOVA, Spearman’s correlation, and linear regression models. Tree species richness and diversity had no significant effect on carbon stocks, while an effect was found on tree density and elevation. The results showed no statistically significant differences in above-and below ground carbon stocks (F = 0.888, p = 0.413) among distance levels from villages while tree density (F = 19.353, p < 0.05) was found to be increasing with increasing distance from the village to the forest. The results suggest that biomass carbon stocks in traditional agroforestry landscape are independent of species richness and diversity, dependent on tree density. The lower tree density, species richness and diversity at immediate distance implies the effect of proximity disturbance. The immediate distance has a greater potential for high biomass carbon accumulation if the disturbance can be minimized and tree density augmented through planting indigenous tree species and conservation.