Grass species composition, yield and quality under and outside tree crowns in a semi-arid rangeland in south-western Zimbabwe

Abstract

A two-year study was conducted in lightly grazed areas of Matopos Research Station, Zimbabwe, to evaluate the impact of widely spaced trees on understorey grass composition, yield and quality. The study trees were Terminalia sericea and Acacia karroo. Ordination techniques using grass density and biomass as indices separated quadrats according to soil type but not grass species according to understorey or open areas or according to tree species. Grass yield under tree crowns was similar to open areas, in contrast with most reports where understorey areas had higher yields. The high understorey grass quality that has been reported from savanna areas exhibiting grass composition differences was not expressed. Selective grazing of palatable perennial grasses growing in association with tree crowns and their eventual replacement by low-yielding and less-palatable grasses that normally grow in open areas is proposed as an explanation of the unique tree-grass interaction scenario of this study. In areas where this replacement has occurred, recovery may require management interventions.

Keywords: annual grasses; botany; crude protein; grasses; Matopos Research Station; quality; semi-arid; soil fertility; species composition; tree-grass interaction; trees; understorey grasses; yield; Zimbabwe; acacia karroo; associations; biomass; composition; grass; grass density; grass quality; grazing; interaction; management; ordination; palatable; perennial grass; rangeland; recovery; savanna; selective grazing; technique; terminalia sericea; tree species; understorey

African Journal of Range & Forage Science, Vol. 15(1 & 2), pp. 23–34