The assessment of invasive alien plant species removal programs using remote sensing and GIS in two selected reserves in the eThekwini Municipality, KwaZulu-Natal

Abstract

The occupation of natural environments by invasive alien plant species (IAPs) are a growing threat to ecosystems. This has resulted in the creation of government-based initiatives to mitigate invasion, however, there has been little progress towards assessing these initiatives. Remote sensing is a commonly used tool in the detection of IAPs; even so, there has also been little research towards its use as a tool to assess mitigation efforts. This study aims to assess the clearing initiatives of three IAPs which are Acacia podalyriifolia, Chromolaena odorata and Litsea glutinosa in two nature reserves (Paradise Valley and Roosfontein) within the eThekwini Municipality, KwaZulu-Natal, (South Africa) using remote sensing. To achieve this aim, image classification using the Maximum Likelihood classifier was performed on both sites before and after clearing to compare density, distribution and area cover. All species were successfully detected in both reserves in both the 2010 and 2015 imagery except L. glutinosa in the Paradise Valley Nature Reserve in 2010. User’s and producer’s accuracy for A. podalyriifolia and C. odorata (Paradise Valley) and C. odorata L. glutinosa (Roosfontein) were more than 70% in both 2010 and 2015, which is above agreed standards. The occurrence and area cover of all species in both reserves decreased substantially except L. glutinosa in Paradise Valley Nature Reserve, which experienced only a slight decrease in area cover. The results indicate that remote sensing is a suitable tool for the assessment of IAP removal strategies. Further research should consider early detection of IAPs to prevent spread.

Keywords: Invasive alien plant species, remote sensing, species detection, removal assessment