C. Van der Waal

Agri-Ecological Services

Species with highly restricted ranges are disproportionately at risk of extinction, particularly where habitat loss occurs as a result of mining. Post‐mining restoration of rare species populations is considered as an appropriate response to counter such threats, but requires a careful, evidence‐based and information‐driven approach. The economical...

Estimating soil texture is a fundamental practice universally applied by soil scientists to classify and understand the behavior, health, and management of soil systems. While the accuracy of both the soil texture class and the estimates of the percentage of sand and clay is generally accepted when completed by trained soil scientists, similar esti...

The scale of resource heterogeneity may influence how resources are locally partitioned between co-existing large and small organisms such as trees and grasses in savannas. Scale-related plant responses may, in turn, influence herbivore use of the vegetation. To examine these scale-dependent bi-trophic interactions, we varied fertilizer [(nitrogen...

Background/Question/Methods The rate, extent and persistence of woody plant encroachment vary at hectare to global scales. Our ability to manage encroachment is constrained by limited knowledge of spatially- and temporally-specific factors. Experimental approaches are insufficient because they capture neither the range of variability in site condi...

Intraspecies dietary flexibility, such as variable consumption of graze vs. browse in herbivores, has received scant attention on a spatial scale despite growing evidence of substantial variability within and among populations, especially in bovids. Here, we report on extraordinary differences in cattle diet among two communal pasture areas across...

Changing land use patterns in southern Africa have potential to dramatically alter the prospects for carnivore conservation. Understanding these influences is essential for conservation planning. We interviewed 250 ranchers in Namibia to assess human tolerance towards and the distribution of large carnivores. Cheetahs (Acinonyx jubatus), leopards (...

Legislative changes during the 1960s–1970s granted user rights over wildlife to landowners in southern Africa, resulting in a shift from livestock farming to wildlife-based land uses. Few comprehensive assessments of such land uses on private land in southern Africa have been conducted and the associated benefits are not always acknowledged by poli...

Forage quality in grassland-savanna ecosystems support high biomass of both wild ungulates and domestic livestock. Forage quality is however variable in both space and time. In this study findings from ecological and laboratory studies, focused on assessing forage quality, are combined to evaluate the feasibility of a remote sensing approach for pr...

Multiple factors determine diet selection of herbivores. However, in many diet studies selection of single nutrients is studied or optimization models are developed using only one currency. In this paper, we use linear programming to explain diet selection by African elephant based on plant availability and nutrient and deterrent content over time....

There is a growing concern that the feeding habits of the African elephant, which include pushing over, uprooting and snapping trees, may have a negative impact on other herbivores. Browsed trees are known to respond by either increasing production (shoots and leaves) or defence (secondary compounds). It is not clear, however, what proportion of th...

1. Scaling theory predicts that organisms respond to different scales of resource patchiness in relation to their own size. We tested the hypothesis that the scale of nutrient patchiness mediates resource partitioning between large trees and small grasses in a semi-arid savanna. 2. In a factorial field experiment, Colophospermum mopane trees and as...

In savannas, the tree-grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and grasses. Nine abandoned livestock holding-pen areas...

1. Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk,...

Elephant and impala as intermediate feeders, having a mixed diet of grass and browse, respond to seasonal fluctuations of forage quality by changing their diet composition. We tested the hypotheses that (1) the decrease in forage quality is accompanied by a change in diet from more monocots in the wet season to more dicots in the dry season and tha...

There is a growing concern that the feeding habits of the African elephant, which include pushing over, uprooting and snapping trees, may have a negative impact on other herbivores. Browsed trees are known to respond by either increasing production (shoots and leaves) or defence (secondary compounds). It is not clear, however, what proportion of th...

Issues of residual spatial autocorrelation (RSA) and spatial scale are critical to the study of species-environment relationships, because RSA invalidates many statistical procedures, while the scale of analysis affects the quantification of these relationships. Although these issues independently are widely covered in the literature, only sparse a...

Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J.Kirk ex Benth.) J.Léonard, in a greenhou...

We analysed stability and predictive capabilities of known nitrogen absorption features between plant material prepared for NIRS (dried) and RS (fresh) studies. Grass spectra were taken of the plant canopy, and again after the grass sample was dried and ground. Models were derived using stepwise multiple linear regression (sMLR). Regression values...

Summary • Globally, both climatic patterns and nitrogen deposition rates show directional changes over time. It is uncertain how woody seedlings, which coexist with herbaceous plants in savannas, respond to concurrent changes in water and nutrient availability. • We investigated competition effects between herbaceous vegetation and tree seedlings (...

A field experiment was conducted in which Mopane (Colophospermum mopane) trees were subjected to three different canopy treatments:felling of trees at a mean height of 0.7m above ground level, felling at a height of 2m, or pruning of selected branches. These treatments were intended to simulate wood harvesting by local communities, pollarding by el...

The origin of differences in growth parameters between impala from the Mara Research Station (Mara) and the Messina Experimental Farm (Messina) was investigated. Impala from both localities were harvested, and body weights (BW) and cold carcass weights (CCW) were measured. The impala were classified into three age classes, young, sub-adult and adul...

The composition of the plant species eaten by kudu (Tragelaphus strepsiceros) determines the diet quality, which impacts on kudu condition and mortality levels. The yearround diet composition of kudus in the Limpopo Province, a mopane (Colophospermum mopane) dominated area, was determined by faecal analysis. The most important dietary plant species...

In deciduous savanna a marked decline in browse availability characterises the late dry season and apparently regulates populations of large browser species such as kudu. The dry season utilisation patterns of two woody species, Acacia tortilis and Boscia albitrunca, in two comparable sites but subjected to different kudu densities, were studied to...

A direct observation technique was used to establish the foraging behaviour of Boer goats, Nguni goats, Pedi sheep and Dorper sheep. According to the Chi-square dissimilarity measure, plant-form (grass, forb, woody) differences between the diets of goats and sheep were greater than differences between the goat breeds and sheep breeds. The results f...

Faecal samples from eight confined kudu populations were collected from May 1999 to December 1999. Samples were analysed for nitrogen concentration. Faecal nitrogen concentration (N1) reached a low during the dry-hot season (August to the end of October) and peaked in November. N1 was negatively correlated with kudu density for samples collected du...

A survey of the extent and impact of game ranching on the natural resources of the Northern Province was conducted during 1998. Approximations of the annual turnover, game numbers and socio-economic impact of game ranching were obtained. Questionnaires were distributed to game ranch owners and managers and exemption permits issued by the Provincial...

A survey of the extent and impact of game ranching on the natural resources of the Northern Province was conducted during 1998. Approximations of the annual turnover, game numbers and socio-economic impact of game ranching were obtained. Questionnaires were distributed to game ranch owners and managers and exemption permits issued by the Provincial...

Agricultural activities are depicted as highly dependent on weather conditions. The need to employ risk management strategies is emphasized leading to the aim of the paper stating that a basic qualitative decision making model should be adopted to ensure timely adjustments to weather conditions. Factors affecting production are discussed. Two model...