Modification of soil nutrients and micro-climate by tree crowns in a semi-arid rangeland of south-western Zimbabwe

Abstract

Tree crowns in semi-arid areas have often been found to create micro-habitants of improved soil physical and nutrient status and reduced evapotranspiration. These encourage the growth of mesic, palatable and high yielding perennial grasses in otherwise arid environments. A two-year study, in areas with a long history of light grazing, at Matopos Research Station sought to establish whether the soil nutrient status and micro-climate under tree crowns are different from those in open areas, and whether the differences are affected by soil type and tree species. The study trees were Terminalia sericea and Acacia karroo. There were consistent patterns in soil nutrient status between understorey and open areas, although these patterns were largely not significant. There was also a consistent pattern in soil volumetric water content of open areas > T. sericea L > A. karroo understorey areas. Tree crowns reduced solar radiation reaching understorey areas by an average of 88% and rainfall by an average of 15%. The findings on soil nutrient status are consistent with results from disturbed systems, and challenge the dogma, at least for soil nutrient status, that conservative stocking rates are beneficial.

Keywords: botany; crown interception; Matopos Research Station; micro-climate; nutrients; semi-arid; shade-adapted; shading; soil nutrient enrichment; soil nutrients; solar radiation; trees; understorey; Zimbabwe; acacia karroo; evapotranspiration; grass; grazing; perennial grass; rainfall; rangeland; soil nutrient status; stocking rate; terminalia sericea; tree species

African Journal of Range & Forage Science, Vol. 15(1 & 2), pp. 16–22