Invasion of Neltuma juliflora (mesquite) and its effects on soil physicochemical properties in a semi-arid rangeland of South Africa

Abstract

Invasive species threaten ecosystem functions in African rangelands by altering soil properties, and affecting overall health and productivity. This study compared soil physicochemical characteristics under invasive Neltuma juliflora and native Vachellia karroo across two zones (beneath tree canopy versus open grassland) to assess their impact on soil health (based on selected physicochemical indicators). Data were collected on surface penetration resistance, soil texture, total carbon, total nitrogen, C/N ratio, pH, available phosphorus, exchangeable cations, and cation exchange capacity. Results showed significantly lower total nitrogen beneath N. juliflora, while total carbon remained unchanged across species and sampling zones. Soil pH was lower beneath tree canopies than in open grasslands, irrespective of species. The C/N ratio and penetration resistance showed no significant differences. V. karroo had higher exchangeable K⁺, and available phosphorus was more abundant under native vegetation, with lower concentrations beneath tree canopies. Soil texture varied, with N. juliflora preferring soils having higher sand content, and N. juliflora-tree canopy interactions increasing cationic sand content. These findings suggest that invasive N. juliflora alters soil properties, particularly nutrient availability and texture, potentially impacting native plant growth and ecosystem stability. Understanding these changes is essential for managing invasive species and restoring native ecosystems in African rangelands.