Distribution of alien plants, their effects on ecosystem structure, and allelopathic effects on Vigna unguiculata Walp: A case of the selected area of the Makhado Municipality, Limpopo Province, South Africa

Abstract

Alien plants are typically species that have been introduced either intentionally or unintentionally to an ecosystem through anthropogenic intervention. Once in an area, they displace native plant species. The main aim of this study was to evaluate the ecology and distribution of alien plants, their effects on ecosystem structure and function, and their potential for ecosystem restoration in Makhado Municipality. Three specific objectives are developed: (a) To evaluate the distribution range of alien plants in Makhado Municipality; (b) Investigation of the interactions of alien plants with some native plants in Makhado area; (c) The assessment of alien plants on Cowpea (Vigna unguiculata (L.) Walp.). An area of 6 hectares of abandoned land previously used for agriculture in Vleifontein within Makhado Municipality was surveyed simultaneously, to determine the distribution of alien plants and their interactions with native plants using nearest neighbour method and quadrants sampling methods. The distribution patterns of the alien plants (Lantana camara L., and Solanum mauritianum Scop) were determined to be both clumpish in the distribution patterns characterized with dense thickets. Aliens were more prevalent than natives in cases where quadrats were laid out. They formed a dense mat promoting bush encroachment and altered the structure of the ecosystem. Allelopathic effects of alien plants assessed by employing seed germination experiment and growth experiment in a greenhouse were carried out as follows: germination of V. unguiculata seeds in petri dishes for two days to test their viability; those that germinated were taken to the greenhouse or field trial facility, where they were grown in plastic bags containing soils from under L. camara and S. mauritianum, and a distance away. The leaf extracts of the two species were used to spray the seeds of Cowpea that were germinated in the laminar chamber, and the seedlings that were grown in plastic bags in a greenhouse. The leaf leachates of the two species suppressed seed germination and seedling growth of V. unguiculata. The impact of the two aliens on native plants in the field was suppressive by affecting the natives negatively in terms of their numbers and sizes. Allelopathic effects from the two aliens were responsible for poor germination and development of natives, and they were also seen to co-exist with each other in the study area.