Effect of encroaching woody plant species on soil nutrients and selected soil chemical properties in communally managed semiarid savanna grazing lands in the North West province, South Africa

Woody plant encroachment is recognised as one of the major threats to biodiversity in ecosystems. In many arid and semiarid areas of South Africa, indigenous encroacher species are proliferating, but the factors that favor their abundance are poorly understood. This study investigated the effect of encroaching woody species on soil properties. The effects of two encroaching species, Senegalia mellifera and Dichrostachys cinerea, on soil nutrients and chemical properties were investigated in 8 communally managed grazing sites and compared to the effects of the non-encroacher, Vachellia karroo, in two non-encroached benchmark sites. Three belt transects were laid out to determine woody plant density. Three soil samples (0-20 cm deep) per belt were sampled to determine soil properties. Senegalia mellifera was the most abundant with a mean density of 5907 TE ha−1. Soil properties in the benchmark sites had no significant differences (p > 0.05) than soil under encroaching D. cinerea regarding organic C, total N, C:N, exchangeable Na, CEC, EC, ESP, SAR and soil texture. Plant influence on soil differed among encroaching species and between encroaching and non-encroaching species. Plant diversity explain the variation of soil properties and prove the important specific role of each species in the ecosystem.