Rangeland degradation in semi-arid Swaziland: effects of dip-tanks on herbaceous vegetation and soil properties

Abstract

This study investigated dip-tank use effects on herbaceous vegetation and soil, and relationships between environmental and species variables. Eight dip-tanks, three each in sandy (DPBS) and loamy (DYRL) soils, and two in stony (ROSG) soils were used. Data were collected at 50, 100, 150, 300, 500, 700 and 900 m from each dip-tank. In DPBS, phosphorus and potassium contents were highest (P < 0.05) on approaching dip-tanks. In all soils, forb and perennial grass abundances showed significant differences but there were no significant trends with distance. These variables are not sufficiently sensitive to form gradients or the gradient is diminished with heavy grazing. In DPBS, the canonical correspondence analysis showed negative correlation of distance with bareness, the abundance of Aristida rhiniochloa and Cynodon dactylon, which may suggest these variables may respond to grazing gradients around dip-tanks, but this pattern was not established on the other soil types. Therefore, caution is required in drawing conclusions of the piosphere effect around focal points. The abundance of highly palatable species was low except for Panicum maximum in DPBS. It is concluded that vegetation and soil changes are driven by abiotic (site and soil) and biotic (livestock) factors that have different influences at different scales. Therefore, any rangeland utilisation and management program should consider these drivers.

Keywords: bare patch, forbs, grass, highly palatable, Lowveld

African Journal of Range & Forage Science 2013, 30(3): 127–140