Trends in NDVI across protected areas in South Africa

Abstract

Vegetation plays a significant role in the environment as it provides provisioning, supporting, and regulating ecosystem goods and services. Vegetation in protected areas in South Africa is experiencing significant changes in structure and composition as a result of human activities and climate changes. It is imperative that vegetation cover is managed and continuously monitored for it to continue to play its role in ecosystems.

This study aimed at investigating the rate and direction of change in NDVI over a 20-year period (2001-2020) inside, and outside, protected areas in South Africa using remote sensing. NDVI is used as a proxy for vegetation cover, and Google Earth Engine was used to assess the NDVI values for each protected area and its buffers. Grouping the protected areas according to biomes, all the biomes of South Africa except the Forest biome were assessed. No protected area was grouped under the Forest biome because the protected areas studied were grouped under the biome which constituted the largest area. Five protected areas were each studied from Grassland, Savanna, Albany Thicket, Nama-Karoo, Succulent Karoo, and Indian Coast biomes. Three and two protected areas from the Fynbos and Desert biomes, respectively, were studied. Linear regression analysis was done to find the trends in NDVI, and correlation analysis was also done to find the relationship of vegetation change between the protected areas and their buffers. The result of the analysis shows that protected areas in all the biomes except the Grassland and Indian Coast experienced negative trends in NDVI values. This translates to 26 out of the 35 protected areas having negative trends in NDVI. Only 10 of the protected areas have more vegetation cover than their buffers (5 km and 20 km). The protected areas with positive trends in vegetation cover change are gaining vegetation faster or losing vegetation slower than their surroundings. Except for the Oviston Nature Reserve and Orange River Mount Nature Reserve, all the protected areas have strong correlation values with their respective buffers ranging from 0.600 to 1.000. More efforts should be focused on protected areas that have negative trends in NDVI as well as those with negative trends in vegetation cover change.