Mapping the occurrence of Chromolaena odorata (L.) in subtropical forest gaps using environmental and remote sensing data

Abstract

Globally, subtropical forests are rich in biodiversity. However, the native biodiversity in these forests is threatened by the presence of invasive species such as Chromolaena odorata (L.) King and Robinson, which thrives in forest canopy gaps. Our study explored the utility of WorldView-2 data, an 8-band high resolution (2 m) imagery for mapping the probability of C. odorata occurrence (presence/absence) in canopy gaps of a subtropical forest patch, the Dukuduku forest, South Africa. An integrated modelling approach involving the WorldView-2 vegetation indices and ancillary environmental data was also assessed. The results showed a higher performance of the environmental data only model (deviance or D 2 = 0.52, p \ 0.05, n = 77) when compared to modelling with WorldView-2 vegetation indices such as the enhanced vegetation index, simple ratio indices and red edge normalized difference vegetation index (D 2 = 0.30, p \ 0.05, n = 77). The integrated model explained the highest presence/absence variance of C. odorata (D 2 = 0.71, i.e. 71 %). This model was used to derive a probability map indicating the occurrence of invasive species in forest gaps. A 2 9 2 error matrix table and the receiver operating characteristic curve derived from an independent validation dataset (n = 38) were used to assess the model accuracy. Approximately 87 % of canopy gaps containing C. odorata were correctly predicted at probability threshold of 0.3. The derived probability map of C. odorata occurrence could assist management in prioritizing target areas for eradication of the species.

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

“…This surface texture affects the reflection of radiation resulting in a unique spectral signature compared to other vegetation present (Kumar, Schmidt, Dury, & Skidmore, 2002). Chromolaena odorata has been successfully detected in other studies using WorldView-2 imagery (Malahlela et al, 2015). Litsea glutinosa is noted to occur in heterogeneous stands when compared to the other two selected species (A. podalyriifolia, and C. odorata) which form dense monotypic stands and is therefore more difficult to detect (Bradley, 2014).…”

“…The shrub species C. odorata a category 1b invader (NEMBA, 2016) is indigenous to Central and North America, it has an allelopathic effect which inhibits seedling recruitment of indigenous species (Malahlela et al, 2015). Further research should consider early detection of IAPs as prevention of spread is more cost effective than combating invasion, therefore remote sensing can be applied as an early detection tool to effectively combat invasion (D'Antonio et al, 2004).…”

“…Therefore regular monitoring of IAPs is required to manage invasion effectively and efficiently, which in turn requires methods that can detect IAPs rapidly and precisely (Müllerová, Pergl, & Pyšek, 2013). Field surveys can be used to map IAPs, however, these are inefficient over larger areas (Malahlela, Cho, & Mutanga, 2015). Aerial photographs have been successful to an extent as they are able to detect IAPs which are unique to other surrounding vegetation (Lass et al, 2005).…”

Antioxidant evaluation and inhibitory activity of Chromolaena odorata leaf extract on hydrogen peroxide-induced erythrocyte hemolysis

“…Due to its high climatic tolerance, the plant is globally distributed [2]. It is spread from Southeast Asia, through the South Pacific into Central and Eastern Africa [2,3].…”

“…Due to its high climatic tolerance, the plant is globally distributed [2]. It is spread from Southeast Asia, through the South Pacific into Central and Eastern Africa [2,3]. The plant is an invasive weed of agriculture and also an aggressive competitor that occupies different types of land where it suppresses young plantations and smothers vegetation [4,5].…”