Impacts of Invading N₂-Fixing Acacia Species on Patterns of Nutrient Cycling in Two Cape Ecosystems: Evidence from Soil Incubation Studies and15N Natural Abundance Values

This study examines the impacts of woody, N₂-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the δ15N natural abundance technique. The results confirm earlier reports that invasion by woody shrubs results in organic matter and nutrient enrichment of surface soils of both ecosystems. However, patterns of nutrient availability (phosphorus and nitrogen) were not necessarily enhanced. In the more fertile standveld both phosphorus and nitrogen (significant at P