Long-term stability of grazing lawns in a small protected area, the Mountain Zebra National Park

Angela Gaylard,Peter Novellie

doi:10.4102/koedoe.v55i1.1108

Abstract

We examined a heavily grazed plant community dominated by creeping grass species with the aim of, (1) determining its response to the exclusion of grazing and (2) its long-term persistence. This plant community was particularly favoured by wild ungulate species that prefer short grasses – blesbok (Damaliscus dorcas phillipsi), springbok (Antidorcas marsupialis) and black wildebeest (Connochaetes gnou). Exclusion of grazing by large herbivores by means of fencing resulted in the virtual disappearance of the creeping grasses and their replacement by tall tufted species. On plots that remained unfenced, the plant species composition was found to be little changed after an interval of more than 20 years. The number large stock unit equivalents (LSU) per ha carried by the plant community was used as a proxy for grazing intensity. Monitored for approximately 2 years at the start of the study, LSU per ha was found to greatly exceed levels recommended for commercial livestock production. This plant community conforms to a recently published definition of a grazing lawn, in that intense grazing promotes palatable, grazing-tolerant grass species.Conservation implications: The positive association between grazers and grazing-tolerant grass species evidently persisted for more than 20 years and there was no evidence of an increase in abundance of unpalatable plant species. Despite the small size of the park, which limited the extent of large herbivore movements, localised heavy grazing did not lead to range degradation.

Highlights

The term ‘grazing lawn’ has been widely used to describe patches that, as a result of frequent, intense grazing, become dominated by short, grazing-tolerant grass species (Archibald 2008; Archibald et al 2005; Cromsigt & Olff 2008; McNaughton 1984; Stock, Bond & Van de Vijver 2009; Waldram, Bond & Stock 2007)
Grazing lawns are characterised by a positive association between grazers and grazingtolerant grasses; intensive grazing has the effect of increasing the productivity and quality of the food resource (Cromsigt & Kuijper 2011)
The results described above are in accordance with evidence in the literature (Archibald 2008; Cromsigt & Olff 2008; Stock et al 2009; Waldram et al 2007) that grazing lawns are animal driven; if grazing is removed the creeping grasses give way to taller bunch grasses

Summary

Introduction

The term ‘grazing lawn’ has been widely used to describe patches that, as a result of frequent, intense grazing, become dominated by short, grazing-tolerant grass species (Archibald 2008; Archibald et al 2005; Cromsigt & Olff 2008; McNaughton 1984; Stock, Bond & Van de Vijver 2009; Waldram, Bond & Stock 2007). Grazing lawns are characterised by a positive association between grazers and grazingtolerant grasses; intensive grazing has the effect of increasing the productivity and quality of the food resource (Cromsigt & Kuijper 2011) It has been demonstrated (Archibald 2008; Cromsigt & Olff 2008; Stock et al 2009; Waldram et al 2007) that grazing lawns do not derive solely from existing matrices of abiotic factors, such as soil heterogeneity ( their distribution may be influenced by such factors), but are animal driven. Patch-selective grazing and grazing lawn formation should be regarded as a desirable phenomenon in grassland systems that are managed with the objective of maintaining biodiversity and natural ecological processes

Methods

Results

Discussion

Conclusion