Threshold changes in the production potential of bush clumps along piosphere gradients in arid thicket mosaics

Abstract

Various studies have noted threshold changes in vegetation composition and structure and soil physical and chemical properties in the Albany Thicket biome of South Africa. The aim of this study is to assess if these changes to the environment have transformed the ecosystem’s forage production potential. To estimate forage production potential we compare three models that make use of the mean and variance of the Normalized Difference Vegetation Index (NDVI) obtained from two WorldView-2 satellite images. For the models, NDVI values were sampled along four independent piosphere gradients that vary in their intensity of use and rest from herbivory. Our results indicate that the model that makes use of NDVI variance after a good rainfall year is able to discern changes in the forage production potential that corroborate threshold changes in the vegetation and soil environment. Our results support the growing body of evidence that increases in the variance of ecosystem processes and services are important indicators of impending threshold changes in social-ecological systems.