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.
Highlights
Herbivore population trends in the Kruger National Park (KNP) over the past century were traditionally explained with reference to decimation by hunting and epizootics (Joubert 2007a; Pienaar 1963), effects of rainfall (Dunham, Robertson & Grant 2004; Owen-Smith & Ogutu 2003; Whyte & Joubert 1988) and predation (Harrington et al 1999; Joubert 2007a, 2007b; Owen-Smith, Mason & Ogutu 2005; Owen-Smith & Mills 2006; Owen-Smith & Mills 2008)
Some results of local research contributed towards the definition of key forage resource indices
Indicators of forage availability Nitrogen productivity: Nitrogen productivity is defined as the quantitative availability of forage items for herbivores of a given nitrogen quality as a result of biomass production
Summary
Herbivore population trends in the Kruger National Park (KNP) over the past century were traditionally explained with reference to decimation by hunting and epizootics (Joubert 2007a; Pienaar 1963), effects of rainfall (Dunham, Robertson & Grant 2004; Owen-Smith & Ogutu 2003; Whyte & Joubert 1988) and predation (Harrington et al 1999; Joubert 2007a, 2007b; Owen-Smith, Mason & Ogutu 2005; Owen-Smith & Mills 2006; Owen-Smith & Mills 2008). The long-term and spatially widespread nature of population trends suggested that over-arching landscape-scale influences may be involved to an as yet unknown extent. Towards this purpose we developed a climate–vegetation response model. This model was developed through interpretation and synthesis of existing knowledge (literature review) and supported by analyses of local patterns of climate effects on forage plant performance and chemical composition. To the extent that different herbivore species have divergent nutritional requirements in respect of these key forage resources, we expected that their population performances would be affected differentially by conditions of the edaphoclimatic environment (spatial scale) and climate (temporal scale)
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