Climate and vegetation in a semi-arid savanna: Development of a climate–vegetation response model linking plant metabolic performance to climate and the effects on forage availability for large herbivores

Abstract

A framework to establish the expected effects of climate on forage quantity and quality in a local savanna system was developed to interpret large herbivore population performance patterns in the Kruger National Park. We developed a climate–vegetation response model based on interpretation and synthesis of existing knowledge (literature review) and supported by investigation and analyses of local patterns of climate effects on forage plant performance and chemical composition.

Developing the climate–vegetation response model involved three main components, namely (1) defining indicators of forage availability to herbivores (nitrogen productivity, nitrogen quality, carbon-nutrient quality), (2) identifying herbivore species guilds of similar nutritional requirements with respect to these indicators [bulk feeders with tolerance to fibrous herbage (buffalo, waterbuck), bulk feeders with preference for high nitrogen quality forage (short grass preference grazers: blue wildebeest and zebra) and selective feeders where dietary items of relatively high carbon-nutrient quality represented key forage resources (selective grazers: sable antelope, roan antelope, tsessebe, eland)] and (3) developing a process model where the expected effects of plant metabolic responses to climate on key forage resources were made explicit.

According to the climate–vegetation response model both shorter-term transient temperature acclimation pulses and longer-term shifts in plant metabolic functionality settings were predicted to have occurred in response to temperature trends over the past century. These temperature acclimation responses were expected to have resulted in transient pulses of increased forage availability (increased nitrogen- and carbon-nutrient quality), as well as the progressive long-term decline of the carbon-nutrient quality of forage.

Conservation implications: The climate–vegetation response model represents a research framework for further studies contributing towards the enhanced understanding of landscape-scale functioning of savanna systems with reference to the interplay between climate, vegetation and herbivore population dynamics. Gains in such understanding can support sound conservation management.