Parallel A: Rangeland Ecology and Management

The Karoo is often regarded as South Africa’s best-kept secret, an arid remote Outback to be left untouched by new developments lest it loses its special character. Covering a good third of South Africa, the Succulent- and Nama-Karoo, however, now face many changes from internal and external factors. It is time to take stock of current knowledge and challenges concerning the Karoo’s ecological and social dimensions. Accordingly, the GSSA has planned to publish a Karoo Special Issue in the African Journal of Range and Forage Science. This Issue boasts an impressive array of information. An overarching lead article is followed by six sections, each with several articles, concerning the following themes: Climate in the Anthropocene, Gharo across History, Long-term Trends and Processes, Dynamics of Current Developments, Farming Impacts, Ecosystem Processes and Rehabilitation, and ends with a Synthesis. Ironically, Karoo ecology has received more scientific attention than its people, and the Karoo Special Issue therefore sets out to merge different disciplines, if not in individual papers bar the transdisciplinary Lead Article, then at least by the arrangement of different articles. The Karoo Special Issue will be published by the end of 2018.

In general Karoo vegetation is known for its resilience. This so-called resilience was up to date not yet quantified. During the past decade, annual rainfall in South Africa varied a lot with a downward trend in certain areas. The question was therefore asked, how are individual Karoo shrub species reacting to variable water availability while also exposed to different frequencies and intensities of defoliation? A greenhouse trial was conducted where Nenax microphylla, a widely distributed Karoo shrub, was exposed to 36 water and defoliation treatment combinations over a period of 12 months. These treatments included a water deficit gradient of four water treatments, three defoliation intensities and three defoliation frequencies. Amongst other measurements, above- and belowground phytomass production, as well as water-use efficiency (WUE) were measured. A lot of data were obtained, which are summarized in this presentation to highlight the most valuable research findings. Water availability proved to be the single most important factor influencing both above- and belowground productivity and accounted for most of the variation in phytomass production data, much more than the defoliation treatments. Increased water availability resulted in exponentially higher productivity which could be ascribed to the expression of a compensatory growth ability by N. microphylla. Increased water deficit resulted in increased root:shoot ratios. This is one of the few studies known where root:shoot ratios for specific shrubs was calculated. Although water deficit decreased root growth, that decrease was less than that observed for the aboveground phytomass production. Defoliation intensity had the lowest impact on productivity, while the impact of defoliation frequency was markedly higher on both above- and belowground phytomass production. Although defoliation intensity accounted for the least variation in data, it might, however, still impact on the physiological functioning of the plant. Infrequent defoliation resulted in shrubs being less sensitive to defoliation intensity. Water use tended to be uneconomical when water is abundantly available resulting in a low WUE. As soil water becomes limited, the plants were expressing awareness to the water deficit by increasing their WUE for improved survival rather than improved phytomass production. Inclusion of belowground phytomass production in WUE calculations increased the WUE by 30%.  Nenax microphylla showed increased WUE under increased defoliation stress, regardless of the watering treatment. This indicates how the plant defends itself, by increased WUE, against the factor that is causing the most harm to its survival at a given time. It was clear that water had the greatest impact on phytomass production of N. microphylla. Unfortunately, land users do not have control over the rainfall, and therefore the water available to Karoo shrubs. On the contrary, two of the most manageable variables that influence plant response to grazing are frequency and intensity of grazing, which the land manager has fully control over. Rainfall interacts strongly with impact of defoliation and it is therefore more detrimental to graze Karoo shrubs when soil-water conditions are unfavourable.

Rainfall and grazing are primary drivers of vegetation composition in the Nama-Karoo.Increased rainfall is directly related to the abundance of perennial grasses, to where Nama-Karoo transitions to grassland. Severe grazing treatments, (e.g. continuous or summer-only), generally result in an increase in grazing-tolerant dwarf shrubs and annual grasses, and a decrease in perennial grasses.Grootfontein lies in the ecotone between the Nama-Karoo and the grassland biomes, and is home to grazing trials that were stocked from 1934 to 2009, and from 1941 to 1985.The area has experienced higher than average rainfall in recent decades.Plant basal cover data collected in the 1960s and 2010s on the two trials allow several hypotheses to be tested: 1) Historical severe grazing (until 1985) limits subsequent grassiness (Grazing Legacy Effect); 2) Severe grazing precludes increases in grassiness, independent of rainfall (Herbivore Trap Effect; and 3) Historically leniently-grazed sites will transition to grassland with increased rainfall (Biome shift effect). Results show that rainfall was lower in the ten years before surveys in the 1960s (350 mm) than before the 2010s (490 mm).The Grazing Legacy hypothesis was supported in that historically severely-grazed sites differed compositionally from historically leniently-grazed sites, despite all sites becoming much grassier. The Grazing Trap hypothesis was not supported, because previously and currently severely-grazed treatments shifted similarly to a grass-dominated stage.The Biome Shift hypothesis was partly supported in that a shift to grassland did occur, but not always, and severity of grazing appeared to have no influence.Results suggest that increasing rainfall has prompted a shift to much increased grassiness and decreased abundance of dwarf shrubs, and that grazing had a smaller secondary effect.This implies that established veld management principles may not apply to the same degree, and that the effects of rainfall, and drought in particular, will be different from what they were in the past.

Habitat heterogeneity is a key driver of herbivore spatial distribution in natural ecosystems. In managed environments the occurrence of herbivore species may be affected by vegetation cover, availability of surface water, as well as human disturbance factors. Understanding the way that animals use available habitat is essential in understanding the ecology of the landscape, therefore essential for sustainable wildlife conservation planning and management. Large areas of the vegetation on Khamab Kalahari Reserve are heavily impacted by human actions before the establishment of the reserve. Broad-scale applications of arboricides (Molopo) transformed large areas of the vegetation layer from closed woodland to open woodland. This study is the first part of a broader study which aims to determine the impact of bush encroachment on the ecosystem and focusses on the way that large herbivores utilise the different habitat types of the reserve. This will provide insight into future impacts of bush encroachment on herbivore populations, and whether management actions like bush clearing can provide suitable habitat to the herbivore populations. Between the years 2014 to 2017, 25 monthly road strip counts were conducted on a predetermined route to establish the distribution of herbivores. Their distribution was plotted on a habitat type map of the reserve. To determine habitat type selection, it was necessary to determine a habitat visibility factor (fh) for each herbivore species. This gave an estimation of the visibility of each herbivores species in the various habitat types. A species visibility area (sv) was also calculated for each herbivores species, which is effectively the surface area of each habitat type along the survey route in which each herbivore species was still visible. The results were analysed using chi-square analysis which calculated the habitat type selection of the selected herbivore species. The results of the analysis indicated distinct differences in the way that different species utilised the different habitat types. Old cattle posts and open woodland on depressions were the most favoured habitat type on the reserve, while dense and closed woodlands on sandy soils were the most disfavoured habitat types. The results also indicated that blue wildebeest, springbok and zebra were the most selective species, while warthog, giraffe and white rhino were least selective about which habitat types they preferred. The avoidance of closed and dense woodland habitat types by most species suggests that expected increases of woody vegetation in the future will have a negative impact on the populations of species like blue wildebeest and springbok. The general avoidance of habitat types on sandy soils further suggests that nutrients likely also play a role, which warrants further investigation. We can conclude that management actions on the reserve should focus on maintaining suitable open habitat if the long-term perseverance of herbivore species is important. Management actions that focus on preventing bush encroachment will be critical for the productivity of the herbivore populations on the reserve.