Small-scale feeding and habitat preferences of herbivore game species in the grassland of the central Free State

English: The fencing of small areas and stocking them with game species is becoming a common tendency in South Africa. The main objective of this study, conducted during the 2003/04 and 2004/05 seasons in a small fenced in game enclosure (78 ha) in the Bloemfontein district, Free State Province, was to determine the small-scale habitat and feeding preferences of springbok (Antidorcas marsupialis), blesbok (Damaliscus pygargus phillipsi) and black wildebeest (Connochaetes gnou) within the same vegetation type. The associations between soil, vegetation and grazing time by these herbivore game species were also determined, as well as whether the simulated influence of Type I herbivores on the sward structure will affect the small-scale habitat preferences of these herbivore species, which are all regarded as Type III species. A relatively homogeneous area of 250 x 200 m (5 ha) in the middle of an open grassland area was selected for intensive study. The selected area was subdivided into twenty experimental plots of 50 x 50 m (0.25 ha), which were permanently marked and allocated an identification code. Analysis of the soil was done to assess the physical properties, ionic content and electrical resistance of the soil in each experimental plot. Plots varied considerably in terms of the chemical content of the soil, which was largely influenced by soil texture. This may account for the heterogeneity of the vegetation of the demarcated area. Prior land use and small-scale variation could also have influenced the soil quality and vegetation. The botanical composition of the herbaceous layer was determined using a wheel point apparatus according to the nearest plant method, based on occurrence. Surveys were done at the end of each growing season (2003/04 & 2004/05). Above-ground dry matter production was determined by harvesting all plants in 20 randomly-selected 0.25 m² quadrates within each experimental plot, and weighing them. Plots on the northern side had a lower number of grass species with a lower grazing value (predominantly Increaser species), while plots on the southern side had a higher number of grass species with a higher grazing value (predominantly Decreaser species). Changes in the botanical composition between the two seasons (an increase in Increaser species) and the decrease in veld condition scores suggest that the veld is over-utilised and in a poor condition, and that stocking rates are currently too high. However, veld in this condition is the preferred habitat of short grass grazers. Therefore, a compromise between short grazing (habitat suitability) and veld in a good ecological condition seems to be the proper approach. The small-scale spatial preferences of the three herbivore game species were studied by making observations, using binoculars, from a parked vehicle during the morning and afternoon. Both springbok and blesbok preferred habitat patches with a high abundance of Increaser species, relatively high species diversity and moderate to low veld condition score. Black wildebeest tended to favour patches with a higher occurrence of Decreaser species, although Increaser species were also relatively abundant in these plots. The preferred experimental plots generally had a low above-ground DM production. The number of habitat patches utilised was highest during the dry season. A modification of the grazed-class method was used to determine the favoured grass species and percentage utilisation during the different seasons. Marked plants were inspected weekly from June 2004 to May 2005, and subjective estimates were given for utilisation using a developed field reference guide. Themeda triandra, Eragrostis obtusa, Panicum stapfianum, E. plana and Digitaria eriantha were the favoured grass species of springbok, blesbok and black wildebeest. Less-favoured species included Brachiaria eruciformis, Cynodon dactylon, E. chloromelas and Setaria incrassata, while non-favoured species included Tragus berteronianus, Aristida bipartita and Cymbopogon pospischilii. Seasonal variation in utilisation was demonstrated, with a larger number of species that were utilised during the rainy season. Associations between soils, the herbaceous layer and time spent grazing indicated that soil texture, and degradation due to over utilisation, were the most important factors that caused spatial variation in the botanical composition of the grassland area. Less-favoured and nonfavoured grass species mainly occurred on heavy clay soil and were closely associated with soil Na, Ca, Mg and K. In contrast, favoured grass species mostly occurred on soil with higher sand and silt content and were closely associated with soil N, C and Zn. Time spent grazing by springbok, blesbok and black wildebeest were closely associated with the favoured grass species (as listed above). To determine the influence of the simulated effect of Type I species on the small-scale habitat preferences, the grass was mown in two plots with a lawnmower at a height of 5 cm, and in another two plots at a height of 15 cm. Each cutting treatment consisted of a plot containing palatable and unpalatable grass species. Observations were conducted as described previously. The simulated influence of Type I species on the sward structure (grass mown at 5cm) of underutilised grassland may facilitate the occupation of such grassland by short grass grazers, particularly blesbok, which previously avoided these areas. Generally, no distinctive changes in the activity of springbok and black wildebeest could be found. It is recommended that stocking rates in the game enclosure be reduced and maintained at sustainable levels to allow the vegetation to recover and reduce further degradation. Continual assessment of the vegetation is essential to monitor further changes in the herbaceous layer and evaluate long-term sustainability of the game enclosure. Similar monitoring is recommended for all small fenced game ranches.