An investigation of the limited distribution of the grazing lawns in Hluhluwe-Umfolozi Park, South Africa
The grasslands and savannas of the Hluhluwe-Umfolozi Park (HUP), South Africa contain unusual 'grazing lawn' communities dominated by short, grazing tolerant grasses. These grazing lawns appear to be highly productive, and support high densities of grazers during the late summer and early winter, but have a very limited distribution within HUP. A review of the grazing literature indicates a similar pattern at the global scale, with grazing lawns absent or rare in almost every grass-grazer system described. Resource limitations responsible for the limited distribution of grazing lawns were investigated. A conceptual model of key processes considered necessary for the formation and persistence of lawns in HUP was developed. Key processes include both frequent and non-selective grazing during the growing season Based on observations that the distribution of grazing lawns within HUP is strongly related to rainfall, it was hypothesized that further key processes control are involved. In areas of lowest rainfall grazing lawns are replaced by a sparse cover of forbs and unpalatable grass species. It was hypothesized that a shortage of mineral nitrogen (N) and / or water are key processes excluding grazing lawn grasses in these environments. In areas of highest rainfall grazing lawns do not form, even where grass communities have been heavily grazed for a year or more. It was hypothesized that below-ground competition for N by the dominant grasses (bunch grasses) prevent the establishment of grazing lawn grasses in these environments.
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