Secondary invasion and weedy native species dominance after clearing invasive alien plants in South Africa: status quo and prognosis

Abstract

Clearing invasive alien plants often facilitates secondary invasion and/or weedy native species dominance instead of native biodiversity recovery. Secondary invasion and/or weedy native species dominance in turn can present significant barriers to restoration by hindering the recovery of key native species. The problem of secondary invasion and weedy native species dominance is ubiquitous and well appreciated globally, but poorly understood in the context of restoration ecology in South Africa. This study uses a two-pronged approach – a literature review plus an expert workshop – to evaluate the knowledge on secondary invasion and/or weedy native species dominance after clearing invasive alien plants in South Africa. Focus is placed on the definition, habits, biomes, target invaders, factors leading to, effects and management of secondary invasion and/or weedy native species dominance. Results suggest that secondary invasion and/or weedy native species dominance are often observed after clearing target invaders but is seldom reported, focused on, identified by name and/or correctly defined. The occurrence of secondary invasion and/or weedy native species dominance is not biome specific and is mediated by factors such as soil physico-chemical legacies of target invaders, availability of propagules in the soil seed bank and surrounding areas, and side effects of the technique used to clear target invaders. Ferns, grasses, herbs, sedges, shrubs, and trees can be secondary invaders and/or weedy native species. Few or no management interventions currently target secondary invasion and/or weedy native species dominance in South Africa. Given the paucity of knowledge on secondary invasion and/or weedy native species dominance in South Africa, there is clearly a need for more research. Practitioners should integrate the management of secondary invasion and/or weedy native species dominance with their overall invasive alien plant clearing efforts. Relevant steps should be taken to include mechanisms and incentives of dealing with secondary invasion and/or weedy native species dominance in the policy on invasive alien plants in South Africa.