Abstract:
Human activities such as the use of powerline servitude corridors for the secure transmission and distribution of electricity alter natural landscapes and change vegetation patterns, and may also encourage the spread of alien plants. The spread of alien plants from one area to another through intentional and unintentional human activities is a serious threat to the world’s biodiversity, including that of South Africa. Vegetation management in powerline corridors in South Africa may be encouraging the spread of invasive alien species. The study therefore aimed to examine whether powerline corridors are encouraging the spread of alien plant invaders. The vegetation communities within and adjacent to powerlines were sampled on the Khakhu line 22KV and Fundudzi 132KV powerlines in Limpopo province, South Africa. The study observed that servitudes or corridors favoured by invasive alien species cross areas close to the urban fabric on productive soils with abundant light. Nine invasive alien species were identified in Fundudzi dominated by common guava Psidium guajava (mean relative abundance 48.7 %), black–jack Bidens pilosa (mean relative abundance 23.4 %), and common lantana Lantana camara (mean relative abundance 15.4 %).
Khakhu only had 6 species of invasive alien species that were dominated by fierce thorn apple Datura ferox (mean relative abundance 17.7 %) and Khaki bush Tagetes minuta (mean relative abundance 67.3 %). Sites closest to human settlements showed higher species richness of invasive species, whilst sites located further away were dominated by L. camara, with much less species richness. The invasive alien species observed along the powerline servitudes generally decreased as one moved away from areas with human activities. Principal Coordinates Analysis (PCoA) first two axis of the selected exploratory variables accounted for 68.0 % of the total invasive alien species abundance variance, with PCO1 and PCO2 accounting for 43.2 % and 24.8 %, respectively. Weak overlaps in the polygons for the two powerline servitudes suggest that alien invasive populations are not similar and were different among sites with five groups being identifiable. The study findings corroborated that mature forestscapes present only low levels of alien invasion. The research findings may, however, be related to the partial redundancy of present day land cover data, and should be investigated further with a more robust data set taking into account the soil types, controls and several environmental variables that might affect the community structuring.
