Spatio-temporal distribution of Vachellia stuhlmannii (Taub.) in Venetia-Limpopo nature reserve – SPOT-imagery

Abstract

The impact of African elephant (Loxodonta africana) on selected woody plants varies from local extirpation to persistence amid continuous utilisation. Species generally selected by elephants and the way they are foraged makes them vulnerable to high utilisation levels. This paper studied the spatial and temporal distribution of Vachellia stuhlmannii in Venetia-Limpopo Nature Reserve using SPOT (Sytéme Pour l’Observation de la Terre) imagery. The spatial pattern distribution of the species was computed using the Spatial Point Pattern Analysis (SPPA) and the Complete Spatial Randomness (CSR) of the species was tested using the Nearest Neighbour Ripley’s K(r) function. Results indicate a significant decrease in the area covered by V. stuhlmannii between 2013 and 2017, with a subsequent decrease in the density of the species. This result was positively correlated (Pearson correlation r₃ = 0.796, P = 0.634) to a decrease in annual rainfall. V. stuhlmannii follows an aggregated spatial pattern, which led to the rejection of the null hypothesis (H_o) test of complete spatial randomness. Limitation of this study is that the results are based on five-year data between 2013 and 2017. This was influenced by the SPOT data used that is made available commercially. It is recommended that further studies evaluate the species distribution and density prior to 2013 to determine whether the decrease is because of other browsers, diseases, elephant impact, decreasing annual rainfall or combination of factors.

Keywords:

• Vlei thorn
• spatial point pattern analysis
• random forest
• nearest-neighbour distances
• Ripley’s K-function

Disclosure statement

No potential conflict of interest was reported by the authors.