Using piospheres to identify, assess and monitor gradients of elephant impact on thicket

Abstract

AbstractOverpopulation in conservation areas with large populations of elephants reduces the diversity of the thicket vegetation of the Eastern Cape Province of South Africa. Monitoring species' specific impacts is a difficult task for reserves. This study investigates whether the Normalised Difference Vegetation Index (NDVI) can be used to evaluate the health of thicket in the Addo Elephant National Park successfully. To achieve this, different browsing intensities of elephants were used to establish a gradient of the full range of utilisation levels on thicket. These were obtained at different distances from the nearest available water sources for Mesic and Valley Thicket types. NDVI values were correlated to an elephant utilisation gradient, which was, in turn, directly related to distance from a water source. The lowest NDVI values (<0.2) were observed adjacent to watering holes where vegetation was completely degraded due to trampling by the daily congregation of animals. The highest NDVI values (>0.5 representing the densest stands of thicket vegetation) were obtained at distances exceeding 7 km from a water source where elephant densities were the lowest within the park. NDVI values could, therefore, be used to identify and monitor gradients of elephant impact on the integrity of thicket.