Calculating stocking rates for game ranches: Substitution ratios for use in the Mopani Veld

Abstract

Determination of carrying capacity for mixed‐ or multi‐species grazing systems is complex. Commonly, each species is compared to the standard large stock unit (LSU) used in conventional agriculture. However, this approach does not allow for ecological separation, and thus overlooks the potential for using the specialised and complementary resource‐use habits of wild ungulates to maximise veld utilisation. The aim of this study was to quantify the overlap in ungulate resource‐use on a game ranch, and to demonstrate how these indices of overlap can be incorporated into substitution ratios for calculating stocking rates. Habitat utilisation patterns of Burchell's zebra (Equus burchelli,), blue wildebeest (Connochaetes taurinus), eland (Taurotragus oryx), gemsbok (Oryx gazella), giraffe (Giraffa camelopardalis), impala (Aepyceros melampus), kudu (Tragelaphus strepsiceros), and warthog (Phacochoerus aethiopicus), were studied on the Messina Experimental Farm. Indices of overlap were determined for spatial distribution, habitat selection, diet composition, and browsing height, and were calculated as the sum of the percentage points from each resource dimension that was common to both species. Grazer and browser animal unit substitution ratios are presented for each of the ungulates using the index of combined overlap, metabolic mass and a reference norm of a blue wildebeest (grazer) and a kudu (browser) respectively. It is proposed that these substitution ratios can be used to calculate stocking rates for game ranches in the Mopani Veld.

Additional index words:

• Animal units
• carrying capacity
• ecological separation
• indices of overlap
• large herbivores
• multi‐species grazing