Resilience modes of an ancient mountain valley grassland in South Africa indicated by palaeoenvironmental methods

Abstract

Grassland ecosystems supporting wildlife and livestock populations have undergone significant transformation in the last millennium. Climate, herbivory, fire, and people are identified as important drivers of ecosystems dynamics; however, grassland resilience has been rarely explored in landscapes with mixed grazing histories. Here we analyse ecosystems states from a South African mountain valley grassland in the last 1250 years using palaeoenvironmental proxies. Our results suggest that a tallgrass phase maintained by climate, people and fire replaced a shortgrass phase driven by indigenous herbivores after ca. 690 cal BP. Furthermore, the tallgrass phase had unpalatable grasses and disturbed soil. We suggest these ecological changes were linked to climate change and arrival of pastoralists in the region. Therefore, our results indicate that human activities may undermine resilience of grasslands and that reversing some changes may be difficult.

Keywords

• alternate stable states
• degradation
• grassland
• fire
• herbivory
• resilience