Influence of leguminous and non‐leguminous woody plants on the herbaceous layer and soil under varying competition regimes in mixed Bushveld1

Abstract

Five plots on sandy soil were thinned to differing tree densities. Three subhabitats were distinguished, viz. under leguminous trees, under non‐leguminous trees, and between tree canopies. Soil under both leguminous and non‐leguminous trees was richer in nutrients (% total N, % organic C, Ca, K, Mg) than between tree canopies. Certain nutrients (K, Mg) also differed between the two canopied subhabitats. The leguminous tree subhabitat had a marginally higher grass biomass than the non‐leguminous tree and the uncanopied subhabitats at high tree densities. This increase was associated with the occurrence of Panicwn maximum. Digitaria eriantha showed no subhabitat preference, whilst Eragrostis lehmanniana and Schmidtia pappophoroides were mostly confined to the subhabitat between tree canopies. Increased tree competition negatively influenced the yield of grasses between tree canopies, but grass yields associated with the canopied subhabitats were only affected at the highest tree densities. Potential tree competitiveness was the most important determinant of grass yield. The importance of N as the main determinant of the Panicum‐tree association was not confirmed by this study.