The rate of recolonization by native plant species after the eradication of invasive alien plant species in Limpopo Province, South Africa

Abstract

Invasive alien plant species found in riparian zones are known to compete with native plant species for water, space, sunlight, and other natural resources by lowering the structural diversity of native vegetation, thereby altering the functioning of plant communities. This may impact on the number and variety of organisms that a certain vegetation type may support. The aim of the study was to investigate the rate of recolonization by native plant species after the eradication of the in situ alien invasive plant species. This was done by measuring the rate of recolonization by native species after the removal of alien invasive species (Chapters 3 and 4), and by identifying factors to consider for recolonization to occur (Chapter 5). By measuring and identifying the above, it was possible to develop an adaptive management plan (Chapter 6) for the study area, which would assist local and provincial conservation agencies in conserving native species that should improve ecosystem dinamics. The study was carried out in the Waterberg and Makhado district municipalities, Limpopo Province, on farms that are highly infested with alien invasive plant species. Seventy-two permanent plots of 10 m2 each were constructed along three transects. The alien tree species in the plots were eradicated during March 2016 via mechanical clearing, and the area periodically monitored over a period of 34 months. The choice for the dimensions of quadrats depended on the size and distribution of the alien invasive trees, which grow in an aggregated form (such as Acacia decurrens and Populus alba) and have small canopies, except for Lantana camara in some cases. The species present (native and invasive alien plant in the quadrats were identified and recorded during March 2016 before removal of the invasive alien plant species. This was done to establish the rate at which the species (native or alien) were germinating. Results from this study indicate that in the case of Acacia decurrens and Lantana camara, recolonization of native species would be possible in the near future with continued monitoring and management, as some native grass and herb species were emerging on the study site. Populus alba proved troublesome due to its ability to reproduce vegetatively through root suckering, which enabled it to subsequently re-occupy the study area in larger numbers than before due less competition from other native and alien species. Therefore, it would require more time to eradicate this species than the other two. It is conclyuded that, the recolonization by native plants is possible, though it needs more monitoring. It is recommended that there needs to be an adaptive management plan that would assist in providing more affective results in ecosystem recovery and conserve the native plant species.