The Influence Of The Resting Of Veld Combined With Game On Previously Overgrazed Vegetation Of The Nama-Karoo

Land managers in the Nama-karoo are constantly faced with the daunting task of managing their land in an economically and ecologically sustainable way. Historically, the land was characterized by seasonal migration of large herds of springbok to the area in search of grazing and water. As such, the system would have received a large concentration of grazers for a specific period that would have moved off to other fertile lands after some time. This “rest period” where no or fewer grazers were present provided the ecosystem the chance to recover to such an extent that it would be able to offer grazing to animals in the next season.

With the settlement of humans in the area, most wildlife species have been replaced by domestic animals, while fences have been erected around farms cutting off any remaining migration routes (Kingdon, 1997). Although some areas are still managed as private game farms, the largest part of the region is farmed with angora goats and sheep.

Incorrect land management practices such as overgrazing and overstocking, together with the variable rainfall, has led to severe degradation of the natural ecosystem in some areas. Linked to this, the invasion of alien plants onto degraded areas causes further degradation of the environment. The result of land degradation is not only loss in natural vegetation and diversity, but also a loss in economic value (Figure 1).

Figure 1. Degraded (overgrazed) land (left) as opposed to natural veld (right). Figure courtesy Leslie Brown.

The Mountain Zebra National Park (MZNP), which was established to protect the then-threatened (currently vulnerable) Cape Mountain Zebra, is located within the Nama-karoo. The Park has been enlarged various times since its establishment and is currently approximately 21,000 ha in size (Brown & Bezuidenhout, 2005). One of the sections incorporated into the Park since 2000, the Jurisdam-Seekoegat section (Figure 2), was previously used for sheep and angora goat farming. After being incorporated into the park, the veld was rested for four years after which the fences were lowered and wildlife introduced into the area during 2005. To determine the effect of grazing by domestic animals versus that of rest together with wildlife on the different ecosystems, we conducted a vegetation classification as well as veld condition survey in 2002 and reassessed the veld condition in 2017. This study, aimed at describing the different plant ecosystems (plant communities) present, their diversity, and the changes in veld condition over this period, was published in the South African Journal of Botany.

Figure 2. View over the Jurisdam-Seekoegat section of the Mountain Zebra National Park. Figure courtesy Leslie Brown.

The study resulted in the description of six major plant communities that are strongly associated with topography and previous land use. Three plant communities are associated with higher-lying areas, one with the drainage lines and valley bottom sections, while two are associated with mid-plateau parts. Almost all the different plant communities have been affected by domestic grazing, with the ones that were more accessible being more frequently utilized than those occurring on steep slopes and higher-lying plateaus.

In terms of diversity, the plant communities located on the higher-lying mountain areas (steep slopes and upper-plateaus) have recorded a higher diversity than the lower-lying areas. Thus, the higher-lying areas have a larger amount of viable plant species populations. The high diversity of the higher-lying areas can be ascribed to various factors. Firstly, because the domestic animals could not reach all these areas that frequently and therefore had a much lower impact on the vegetation. Secondly, the steep rocky areas (Figure 3) found in these communities provide different microhabitats suitable for a variety of woody species, grasses, and herbs to grow.

Figure 3. Typical steep rocky areas within the study area and the rest of the Park. Image courtesy Leslie Brown.

Whereas both the lower-lying and drainage areas have on average similar species richness to that of the higher lying areas, they differ in terms of the ecological classes. The lower-lying areas consist mostly of pioneer and secondary successional species which have become established due to the past heavy overgrazing that took place in these areas. In contrast, the higher-lying areas comprise mostly climax and late secondary successional species, indicating these areas to be near pristine and in an ecologically stable condition. Figure 4 indicates the different development stages of plant communities in a natural condition when exposed to various degrees of grazing.

Figure 4. The different stages of vegetation degradation as a result of various grazing intensities. Figure courtesy Leslie Brown.

In terms of veld condition, the higher-lying area and in particular the higher-lying plateau areas, achieved the highest veld condition scores, while the lower-lying areas and in particular the drainage channels and valley-bottom areas, had the lowest scores. The low scores of these areas can be attributed to the previous overgrazing by domestic animals while the drainage channels and valley-bottom areas are frequented by all animals for water drinking purposes which explains its low veld condition scores.

When the veld condition scores of 2002 for the different areas are compared with the veld condition scores of 2017, they all showed an increase (Figure 5). The veld condition scores of the lower-lying areas and drainage lines & valley bottom areas were all below 40% in 2002, indicating poor veld conditions while that of the higher-lying areas were 50% indicating moderate conditions. With the rest and game utilization, the veld conditions for all areas improved with the lower-lying areas and drainage lines & valley bottom areas increasing to 51% and 47% respectively indicating moderate conditions. The higher-lying areas achieved a veld condition score of 64% indicating veld in a good condition.

Figure 6. Veld condition scores (%) for the different areas of Mountain Zebra National Park between 2002 and 2017. Figure courtesy Leslie Brown.

The results of this study show that higher-lying mountainous areas provide various micro-habitats for plant species and also act as refuge areas for a variety of plant species. This is reflected in the high species diversity and mostly climax species present in these areas. It also. The increase in veld condition in all ecosystems of the study area emphasizes the importance of resting overgrazed veld and then stocking such areas according to the ecological carrying capacity. The above average rainfall experienced during the resting period also assisted the recovery of the veld. An overall increase in veld condition has also resulted in an increase in carrying capacity of the area which from a farmer’s perspective also increase the economical value of the land. The lower-lying areas although increasing in veld condition still comprise pioneer and secondary successional species.

Although not tested in this study, the soil nutrient status of these areas might be low due to the previous overgrazing, which could prevent further succession to an improved ecological and economical condition. The authors are also in the process of determining the cost effectiveness and success of applying rehabilitation techniques on these lower-lying areas in an attempt to improve its natural ecological state.

References:

1. Brown, L.R., Bezuidenhout, H., 2005. A vegetation description and classification of the farms Ingleside and Welgedacht on the Mountain Zebra National Park, Eastern Cape. Koedoe 48, 23-42.
2. Kingdon, J., 1997. The Kingdon field guide to African mammals. Academic Press Ltd, London.
3. Brown, L.R., & Bezuidenhout, H. 2018. Ecosystem description and diversity of the Jurisdam-Seekoegat sections of the Mountain Zebra National Park, South Africa. South African Journal of Botany 118: 166-178 https://linkinghub.elsevier.com/retrieve/pii/S0254629918310135