Showing papers by "Barend F.N. Erasmus published in 2012"

Human-modified landscapes: patterns of fine-scale woody vegetation structure in communal savannah rangelands.

Abstract: Despite electrification, over 90% of rural households in certain areas of South Africa continue to depend on fuelwood, and this affects woody vegetation structure, with associated cascading effects on biodiversity within adjacent lands. To promote sustainable use, the interactions between anthropogenic and environmental factors affecting vegetation structure in savannahs need to be understood. Airborne light detection and ranging (LiDAR) data collected over 4758 ha were used to examine woody vegetation structure in five communal rangelands around 12 settlements in Bushbuckridge, a municipality in the Kruger to Canyons Biosphere Reserve (South Africa). The importance of underlying abiotic factors was evaluated by measuring size class distributions across catenas and using canonical correspondence analysis. Landscape position was significant in determining structure, indicating the importance of underlying biophysical factors. Differences in structure were settlement-specific, related to mean annual precipitation at one site, and human population density and intensity of use at the other four sites. Size class distributions of woody vegetation revealed human disturbance gradients around settlements. Intensity of use affected the amplitude, not the shape, of the size class distribution, suggesting the same height classes were being harvested across settlements, but amount harvested varied between settlements. Highly used rangelands result in a disappearance of disturbance gradients, leading to homogeneous patches of low woody cover around settlements with limited rehabilitation options. Reductions in disturbance gradients can serve as early warning indicators of woodland degradation, a useful tool in planning for conservation and sustainable development.

Changing distributions of larger ungulates in the Kruger National Park from ecological aerial survey data

Abstract: Documenting current species distribution patterns and their association with habitat types is important as a basis for assessing future range shifts in response to climate change or other influences. We used the adaptive local convex hull ( a -LoCoH) method to map distribution ranges of 12 ungulate species within the Kruger National Park (KNP) based on locations recorded during aerial surveys (1980–1993). We used log-linear models to identify changes in regional distribution patterns and chi-square tests to determine shifts in habitat occupation over this period. We compared observed patterns with earlier, more subjectively derived distribution maps for these species. Zebra, wildebeest and giraffe distributions shifted towards the far northern section of the KNP, whilst buffalo and kudu showed proportional declines in the north. Sable antelope distribution contracted most in the north, whilst tsessebe, eland and roan antelope distributions showed no shifts. Warthog and waterbuck contracted in the central and northern regions, respectively. The distribution of impala did not change. Compared with earlier distributions, impala, zebra, buffalo, warthog and waterbuck had become less strongly concentrated along rivers. Wildebeest, zebra, sable antelope and tsessebe had become less prevalent in localities west of the central region. Concerning habitat occupation, the majority of grazers showed a concentration on basaltic substrates, whilst sable antelope favoured mopane-dominated woodland and sour bushveld on granite. Buffalo showed no strong preference for any habitats and waterbuck were concentrated along rivers. Although widespread, impala were absent from sections of mopane shrubveld and sandveld. Kudu and giraffe were widespread through most habitats, but with a lesser prevalence in northern mopane-dominated habitats. Documented distribution shifts appeared to be related to the completion of the western boundary fence and widened provision of surface water within the park. Conservation implications: The objectively recorded distribution patterns provide a foundation for assessing future changes in distribution that may take place in response to climatic shifts or other influences.

Dry season browsing by sable antelope in northern Botswana

Abstract: The late dry season is a crucial period for grazing ungulates because the nutritional value of the remaining brown grass is lowest then and levels of crude protein and digestible organic matter may fall below the maintenance requirements of herbivores (Owen-Smith, 1982). During this adverse period, mixed feeders like impala (Aepyceros melampus) increase the proportion of browse in the form of the leaves of the woody plants they consume (Owen-Smith & Cooper, 1985). Crude protein levels are generally higher and seasonally more constant in foliage of woody plants than in grasses (Owen-Smith, 1982), but the foliage is commonly defended by tannins or spines that restrict consumption by grazers not adapted to cope with them (Cooper & Owen-Smith, 1985, 1986; Cooper, Owen-Smith & Bryant, 1988). Sable antelope (Hippotragus niger) are predominantly grazers and are distributed throughout southern African savannahs (Estes, 1991; Skinner & Chimimba, 2005) where the dry season is prolonged and ambient temperatures are high before the rains begin. Grass quality is especially poor on infertile, sandy soils (Bell, 1984). Sable typically depend on green grass persisting in drainage sump grasslands or in recently burned areas during the dry season (Estes & Estes, 1974; Parrini & Owen-Smith, 2009). However, contrary to previous reports, we observed a substantial amount of browsing by sable in our study area during the dry season. Here, we quantify the contribution made by browse to the diet of sable in our study area. Methods

Impacts of communal fuelwood extraction on LiDAR-estimated biomass patterns of savanna woodlands

Abstract: This study investigated the biomass patterns and sustainability of fuelwood extraction in the Lowveld of South Africa, where rural households are highly dependent on fuelwood from savannas. The objectives of this study were (i) to compare LiDAR-derived biomass between communal areas and references sites in conservation areas, and (ii) to investigate the sustainability of various future scenarios of fuelwood consumption, using a village-specific, supply-and-demand model based on biomass maps and socio-economic data. On granitic substrates the communal rangelands had an average of 12 ton/ha, which is less than half the biomass of the conservation sites. Under the current rate fuelwood consumption, i.e. 67% of households using fuelwood exclusively at an average of 3.5 ton per household per year, all biomass in the investigated site would be depleted within twelve years. Therefore, policies and interventions that promote the diversification of affordable energy alternatives and rural economic development are desperately needed.