Seriphium plumosum modeling data_HT Pule
Description
Seriphium plumosum L. is an indigenous encroaching shrub that threatens the productivity and ecological functioning of South African grasslands. However, the environmental factors governing its occurrence and encroachment intensity remain poorly understood. This study identified the environmental drivers of S. plumosum occurrence and density in the semi-arid grasslands of Gauteng Province, South Africa. Paired encroached and un-encroached sites were established on 34 randomly selected farms (68 sampling sites). Topographic, soil, vegetation and rangeland condition variables were measured at each site. Conditional logistic regression was used to identify predictors of S. plumosum occurrence, while ordinary least squares regression explained variation in shrub density within encroached sites. Encroached sites had significantly lower herbaceous basal cover (60.2 %± 5.52 (SE)) and soil calcium concentration (183. 3 mg kg⁻¹ ± 7.53) than un-encroached sites (73. 3 % ± 4.74 and 355.4 mg kg⁻¹ ± 54.49, respectively). The probability of shrub occurrence declined with increasing basal cover and soil calcium concentration, with soil calcium emerging as the strongest predictor (β = −0.86 ± 0.40, P = 0.03). Within encroached sites, shrub density declined with increasing veld condition score (β = −0.0178 ± 0.0085, P = 0.044; adjusted R² = 0.093). These findings indicate that the environmental factors influencing shrub establishment differ from those regulating encroachment intensity. Soil calcium is the principal predictor of S. plumosum occurrence, whereas veld condition score best explains variation in shrub density after establishment. These predictors provide a robust basis for developing spatially explicit encroachment-risk models and decision-support tools for sustainable rangeland management.
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Seriphium plumosum L. is an indigenous encroaching shrub that threatens the productivity and ecological functioning of South African grasslands. However, the environmental factors governing its occurrence and encroachment intensity remain poorly understood. This study identified the environmental drivers of S. plumosum occurrence and density in the semi-arid grasslands of Gauteng Province, South Africa. Paired encroached and un-encroached sites were established on 34 randomly selected farms (68 sampling sites). Topographic, soil, vegetation and rangeland condition variables were measured at each site. Conditional logistic regression was used to identify predictors of S. plumosum occurrence, while ordinary least squares regression explained variation in shrub density within encroached sites. Encroached sites had significantly lower herbaceous basal cover (60.2 %± 5.52 (SE)) and soil calcium concentration (183. 3 mg kg⁻¹ ± 7.53) than un-encroached sites (73. 3 % ± 4.74 and 355.4 mg kg⁻¹ ± 54.49, respectively). The probability of shrub occurrence declined with increasing basal cover and soil calcium concentration, with soil calcium emerging as the strongest predictor (β = −0.86 ± 0.40, P = 0.03). Within encroached sites, shrub density declined with increasing veld condition score (β = −0.0178 ± 0.0085, P = 0.044; adjusted R² = 0.093). These findings indicate that the environmental factors influencing shrub establishment differ from those regulating encroachment intensity. Soil calcium is the principal predictor of S. plumosum occurrence, whereas veld condition score best explains variation in shrub density after establishment. These predictors provide a robust basis for developing spatially explicit encroachment-risk models and decision-support tools for sustainable rangeland management.
Institutions
- Agricultural Research Council of South AfricaGauteng, Pretoria