The effects of abiotic factors in South African semi-arid grassland communities on Seriphium plumosum L density and canopy size

Abstract

Most studies suggest that multiple factors are responsible for woody plant encroachment, but are inconclusive on its causes. Woody plant encroachment is modified by local patterns of disturbance, topography, soil texture and fertility, and their relative importance and interaction strength varies among locations. We used grassland communities, Carletonville Dolomite Grassland (CDG), Rand Highveld Grassland (RHG) and abiotic factors (Soil Organic Carbon (SOC), Total nitrogen (TN), Phosphorus (P), Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg) and pH) to investigate habitat preferences of Seriphium plumosum L. in South African semi-arid grassland. Grassland community had a significant effect on S. plumosum density, canopy size, and on components of soil fertility (P< 0.05). Slope position had a significant effect on S. plumosum density and canopy size (P< 0.05). Seriphium plumosum density was significantly lower (23 plants/50 m2±2.39 (SE)) in CDG than in RHG (40 plants/50 m2±4.19). By contrast, S. plumosum canopy size was significantly higher (1.39 m2±0.11) at CDG than at the RHG (1.06 m2±0.08). The interaction of grassland community and slope position had a significant effect on S. plumosum density and soil sodium content (P< 0.05). Bottom slope regions in RHG (59.00 plants/50 m2±8.62) had higher S. plumosum density than bottom slope regions (19.75 plants/50 m2±3.01) in CDG. Soil sodium content was similar in CDG slopes and higher than in RHG slopes. Seriphium plumosum density was positively related to components of soil fertility; P (r2 = 0.1270; P 0.0036), K (r2 = 0.0786; P 0.0237), Na (r2 = 0.0686; P 0.0350), Ca (r2 = 0.0681; P 0.0358), and SOC content (r2 = 0.0669; P 0.0374). However, Seriphium plumosum canopy size did not show any relationship with components of soil fertility. This study revealed that S. plumosum density in grassland communities increased with increasing soil texture and fertility.