Effects of alien plant invaders on native ecosystems are widely acknowledged, although the evidence is sometimes speculative, especially in riparian zones. We examined the changes in floristic diversity, stand structure and composition of resident species associated with invasions of Eucalyptus camaldulensis in riparian zones of the Western Cape, South Africa. Using a gradient comparative approach, we compared the richness, diversity (H 0 ) and evenness (J) of resident vegetation in a riparian forest under varying levels of E. camaldulensis percentage canopy cover. We found that species richness, diversity and structural attributes (e.g. height, relative cover and mean basal area) of native species decreased consistently along the invasion gradient. However, evenness did not change significantly with increasing Eucalyptus invasion. Invasion by E. camaldulensis was associated with changes in native plant species composition; although some native species occurred in alien invaded sites, they were more abundant in uninvaded sites. This research offers a baseline from which further experimental work can be conducted to determine the mechanisms responsible for changes attributed to Eucalyptus invasion.

Many invasive alien plants alter soil‐nutrient regimes of invaded ecosystems, affecting management outcomes. We assessed the effects of Eucalyptus camaldulensis invasions on physical and chemical properties of riparian soils in the Western Cape Province, South Africa. Samples were collected from topsoil beneath the canopy of uninvaded and a gradient of invaded sites, namely, light, moderate and heavy over four seasons. We quantified soil moisture, temperature, litter depth and thickness, primary textural components, concentrations of soil macro (C, N, P and K) and micro (Mn, Zn, Cu and Fe) nutrients, and pH. Available N (NO3−‐N and NH4+‐N) and P, as well as exchangeable Ca and Mg were also assessed. Soil pH levels were significantly lower in invaded than in uninvaded sites in all seasons. Soil moisture decreased consistently with invasion intensity. Concentrations of macro, micro and available nutrients did not vary significantly along the invasion gradient (p > 0.05), but exchangeable cation content was significantly higher in uninvaded than in invaded sites, especially in winter and spring. Sites invaded by E. camaldulensis had higher litter build‐up than non‐invaded sites, but this appears to have little effect on soil‐nutrient regimes. It appears that restoration following removal of invasive stands of E. camaldulensis will not require major interventions to return soil to pre‐invasion conditions. Copyright © 2014 John Wiley & Sons, Ltd.

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