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-habitats 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 > 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.

Frequent fires intensify soil crusting: physicochemical feedback in the pedoderm of long-term burn experiments in South Africa

“…First and foremost, inputs of organic matter to the soil are reduced by burning because of the combustion of aboveground biomass and leaf litter. Secondly, the removal of vegetation tends to increase the number of wetting and drying cycles in the soil surface, due to greater soil temperature (Savage and Vermeulen, 1983) and less interception of rainfall in the exposed post-fire environment (Moyo et al, 1998). This in turn increases the rate of mineralisation of organic matter, a process known as the Birch (1958) effect.…”

Declining soil quality in South Africa: effects of land use on soil organic matter and surface crusting

“…The direct effect is a reduction in inputs of litter and root biomass. Indirectly, however, the effect of temperature (Du Preez & Snyman, 1993), wetting and drying cycles (Birch, 1958;Savage & Vermeulen, 1983;Du Preez & Snyman, 1993;Jordaan & Rautenbach, 1996;Moyo, Frost & Campbell, 1998), possible inhibitory effects of plant roots on microbial activity and the sometimes excessive removal of N relative to C (Theron, 1951) may all contribute to a decline in SOM when vegetation is removed. Theron (1951) showed that grass leys had a reduced rate of mineralisation relative to fallow soils, which he ascribed to the release of antibacterial exudates from grass roots.…”

Impacts of Agroforestry on Soil Chemical Properties in Dinajpur Forest Division of Bangladesh

“…Subsequent nutrient release from leaves, twigs and roots may have an important influence on the organic matter and nutrient budget of the soil (Szott et al, 1991;Young, 1989). Tree crowns in semi arid areas have often been found to create microhabitats of improved soil physical and nutrient status and reduced evapo-transpiration (Moyo et al, 1998). The presence of tree canopies increases soil organic carbon content, moisture availability and nutrient status (Anil et al, 1998).…”