Ecology, Environment and Conservation Paper

Vol 27, Issue 4, 2021; Page No.(1551-1562)

HUMAN SETTLEMENT, ROAD AND RIVERS RATHER THAN CLIMATE DETERMINE THE DISTRIBUTION OF GIANT MILKWEED, CALOTROPIS PROCERA (APOCYNACEAE) IN THE VHEMBE BIOSPHERE RESERVE, LIMPOPO PROVINCE, SOUTH AFRICA

Sipho Glen Mbambala, Milingoni Peter Tshisikhawe, Peter John Taylor and Sebataolo Rahlao

Abstract

Alien plant invasion is one of the increasing threats to plant biodiversity and ecosystem services globally. Anthropogenic activities disturb ecosystems and cause a shift in community assemblages. In recent decades climate change has become the driving force in the disruption of ecosystems and the loss of species diversity, and in promoting species extinction and the spread of alien invasive plant species. In South Africa, 161 out of 8750 plant species are problematic and causing threats to biodiversity and 117 out of 161 alien invasive species are well-established and are widespread. Population counts of Calotropis procera were conducted for each kilometer consecutively for 20 km and 10 km on paved and unpaved road, respectively in the former Mutale Municipality of Vhembe District, Limpopo Province, South Africa. The existing GBIF (Global Biodiversity Information Facility) dataset of Calotropis precera historical collections from around the world was used to model the species distribution globally and in Southern Africa. Maxent 3.3.3k was used to model habitat suitability and the predicted current distribution of Calotropis procera using their distribution records after preparing and projecting to Albers equal area projection for the world. Four Bioclim climatic variables, Bio 1 (Annual Mean Temperature), Bio 4 (Temperature Seasonality), Bio 5 (Max Temperature of Warmest Month), and Bio 12 (Annual Precipitation) obtained from Worldclim database were used. QGIS 2.18.20, was used to create distribution maps of South Africa and Vhembe Biosphere Reserve (VBR) in relation to the position of roads, rivers and settlements. The total transformed areas (settlements), as well as roads and rivers, show new records of Calotropis procera fall in areas predicted to have low suitability. This study concludes that human settlements, urbanization, rivers and road construction influences the current distribution of Calotropis procera in the VBR.