People, environment and biodiversity

We begin this essay with reflections on major research themes highlighted by the Karoo Special Issue (KSI). These include concerns over land-use change, long-term monitoring, climate change, governance and the need for more interdisciplinary research. We also identify some of the novel contributions of the KSI around these themes and highlight research issues that require further attention. These include greater focus on the social-ecological impact of large-scale infrastructural developments and wildlife ranching, as well as the need for more longitudinal studies related to contemporary social issues. We conclude by outlining a simple framework for thinking about interdisciplinarity in future research efforts in the Karoo. The first axis relates to the natural science/social science continuum, while the second is concerned with the continuum between basic and applied science. Greater awareness of these two dimensions could not only encourage researchers to reflect more carefully on where their research fits in relation to the broader research needs of this region but could also promote interdisciplinarity within the research community. It could also bring researchers closer to the realities and needs of the people who live in and derive their livelihoods from Karoo environments.

Strip mining in arid ecosystems causes extreme ecological destruction that may take decades to recover. The present study examined the effect of different plant-community rehabilitation treatments on arthropods after strip mining in the arid Namaqualand region of South Africa. Vegetation cover and plant species richness were significantly lower at all rehabilitated sites compared with those at a reference site. Arthropod species richness did not differ amongst the different treatments and the reference site. Except for the most recently rehabilitated site, arthropod abundance in all guilds was higher at all treatments compared with that of the reference site. Overall arthropod abundance was positively correlated to plant cover and negatively correlated to plant species richness, but these vegetation characteristics had no effect on arthropod species richness. This may be explained by a high cover of pioneer plants at the rehabilitated sites, which offer ample food for generalist arthropod taxa. Arthropod community composition differed significantly between treatments. We demonstrate that rehabilitation of ecosystem function after mining in arid systems is a lengthy process, even after implementation of intensive rehabilitation protocols. We also show that arthropod communities provide additional insights into the level of ecosystem recovery otherwise obscured when only considering plant community data.

The success of different rehabilitation treatments following surface mining on the arid west coast of South Africa was assessed. Treatments consisting of one or a combination of topsoil addition, plant translocation and seeding were applied to experimental rehabilitation sites in 2001, while the treatment of another site in 2008 combined all three techniques. Vegetation and species cover, species richness, diversity and evenness, and grazing capacity of rehabilitation sites were sampled during winter 2009 and summer 2010, and compared with a reference site. All rehabilitated sites achieved the objective to attain a minimum grazing capacity of 20 ha per small stock unit. Rehabilitation trials were successful in establishing a vegetation cover, but were unable to return species richness and diversity to reference levels and did not resemble the reference site in species composition. Common species in reference sites were absent or only occurred in low numbers. No treatment outperformed the others and further experimentation is needed to determine the most suitable combination. It is recommended that rehabilitation should be done in multiple stages in future to improve seedling survival and to return species that are unable to establish in the adverse conditions present at the onset of rehabilitation.

Very few soil seedbank studies have been conducted in South Africa, especially in arid rangelands. Insight into the soil seedbank could therefore improve assessment of rangeland dynamics and enhance rehabilitation efforts. This study aimed to characterise the soil seedbanks in various vegetation types of the Tankwa Karoo National Park, an arid environment in South Africa. At 43 sites soil was sampled twice at the end of spring and the end of autumn, and the composition and structure of aboveground vegetation were described at the peak growth period in spring. Seeds were isolated from the soil samples by means of flotation in a salt solution, seedbank species composition was obtained by seedling germination, and the vegetation was investigated using a line-point survey method. Overall seed density was 8 034 seeds m−2 of which 55% was viable, and the common life-forms were therophytes and chamaephytes. Species richness and diversity were lower in the seedbank compared with those of the vegetation, and the two vegetation spheres were 25% similar. While seedbank composition suggested poor veld condition, there was enough seed density and viability for future regeneration and rehabilitation initiatives. However, this may be impeded by the absence of many perennial species in the soil seedbank.

The Succulent Karoo is characterised by a dense coverage of biological soil crusts (biocrusts) belonging to different types and successional stages. Whereas the Soebatsfontein region hosts cyanobacteria-dominated and minor amounts of lichen- and bryophyte-dominated biocrusts, the Knersvlakte comprises a rich cover of hypolithic crusts growing on the sides and undersides of quartz pebbles. Apart from dominating photosynthesizers used to classify biocrusts, each crust type hosts a rich and specific fungal and bacterial community and also diverse protists. In a remote-sensing mapping approach, soil-inhabiting biocrusts of the Soebatsfontein region covered ∼27% of the surface area, whereas in the Knersvlakte soil-inhabiting biocrusts covered ∼16% and hypolithic biocrusts ∼42% of the region. Combining these data with biomass contents, results suggested that the Knersvlakte, despite somewhat harsher environmental conditions, harboured about 65% more biocrust biomass per surface area. In physiological measurements we observed that biocrusts emit the reactive nitrogen compounds nitric oxide and nitrous acid, showing water pulse-dependent emission patterns. In addition, CO2 gas fixation showed characteristic type-specific patterns depending on climatic conditions. Long-term microclimate measurements along a gradient revealed that forecasted climate and land-use change may be detrimental for biocrusts with potentially adverse effects on soil stability and overall fertility of the Succulent Karoo.

Understanding how climate change and land transformation may impact the distribution and diversity of wildlife species requires landscape-level foundational biodiversity surveys. The Karoo BioGaps Project aims to provide such data and to support the scientific assessment for shale gas development projects in the Karoo basin. In this paper we present the findings of the BioGaps mammal survey, which recorded medium and large mammals across twenty-five 1 km × 1 km sampling sites within the proposed fracking footprint using camera trapping techniques. We use sample rarefaction curves, non-parametric species richness estimators and non-metric multidimensional scaling plots to explore both species richness and community structure. We also used a generalised linear model to investigate how species diversity varies with both site-specific and landscape-level predictors. A total of 38 species were recorded at the majority of sites. Longitude (z = 4.018, p = 0.0005) emerged as the best predictor of species diversity across the study area, which we suggest is linked to the clear east–west aridity gradient. Together these results reveal the cosmopolitan distribution of the mammal taxa in the Karoo and could be used to inform decision-making linked to mining activities in the area.

Impacts of livestock farming include effects on arthropods and a range of related ecological processes. Grazing by sheep may indirectly affect web spider populations by changing vegetation structures available for web construction, or directly by trampling the spiders or their webs. We tested these two potential impacts by surveying spiders along transects and found that web spider abundance was 52% lower in a sheep grazing area compared with inside the adjacent Tierberg-LTER (Long Term Ecological Research) sheep exclosure. This reduction in web-spider abundance could be due to the 10% lower shrub cover in the sheep pasture than in the exclosure. Further support for the hypothesis that web spider abundance is affected by shrub cover came from spider abundance being higher on densely vegetated mounds, termed heuweltjies, than in the surrounding shrub matrix in both the exclosure and the sheep pasture, with heuweltjies showing cross-fence differences, consistent with grazing impacts. In addition, there may be a direct effect of trampling, as suggested by experimental removal of webs. By depressing spider populations, sheep grazing may affect a number of ecological factors, such as trophic relationships or nutrient cycling.

Plant growth forms likely respond differently to disturbances such as trampling. We investigated the trampling effect of 1 600 sheep encamped at night in temporary enclosures (kraals, corrals or pens), which were relocated weekly. To examine trampling effects and regeneration rates of the various growth forms we compared vegeta- tion composition, canopy cover and foliar nitrogen inside and outside kraals, between one and 12 months after the trampling event. We predicted that inside kraals (1) succulent and non-succulent shrubs would be affected more severely than grasses, (2) perennial plant cover would decrease compared with annual plant cover, (3) foliar nitrogen concentrations would increase, and (4) vegetation recovery would be affected by time and rainfall since last use of the kraal. Grasses and shrubs (succulent and non-succulent) responded differently to kraaling. Density and diversity of succulent and non-succulent shrubs decreased, while annual and perennial grass cover inside and outside kraaling areas did not differ. Foliar nitrogen was greater inside kraals. Both succulent and non-succulent shrub cover increased over time after kraaling irrespective of the rainfall. Our study demonstrates that short-term intensive trampling and dunging creates nutrient-rich, heterogeneous patches that may enhance restoration of degraded production landscapes.

The Succulent Karoo biome is a renowned centre of biodiversity and endemism in the arid winter rainfall region of South Africa that is threatened by climate change. On 20 permanently marked plots within a biodiversity observatory, species richness and cover were assessed annually from 2002 to 2017 during the growing season. We were interested, firstly, in whether the vegetation showed any trends in response to the strong decrease in grazing pressure, which occurred at the beginning of the monitoring period, and secondly, in the effect of seasonal climate on the vegetation. We analysed the responses of species richness and cover in four life forms to seasonal rainfall and the standardised precipitation–evapotranspiration index (SPEI) using linear mixed-effect models. Time had a positive effect on richness of annual species and a negative effect on cover of shrubs and annuals, which increased in response to SPEI and less strongly to rainfall during autumn and winter. Habitat did not have any effect and geophytes and perennial herbs did not show any significant response. The importance of SPEI during autumn and winter is discussed in relation to potential germination cues and the projected decrease in rainfall and increase in temperature during these seasons.

Because vegetation change in arid ecosystems is slow, long-term data are essential to gain an understanding of how the vegetation responds to short-term, inter-annual variation in rainfall; long-term cyclic rainfall patterns; and grazing pressure. The point intercept method was conducted annually over a period of more than 20 years at five transects in the plains habitat on the Goegap Nature Reserve in the Northern Cape, South Africa. Vegetation change was assessed in terms of vegetation cover, species composition, species abundance, growth form composition, range condition and plant diversity. Non-metric multidimensional scaling was used to illustrate the trajectories in floristic data and to determine the strength of the correlations with rainfall and grazing variables. The effects of the high grazing pressure on the plains were apparent in the overall decrease in total plant cover and reductions in the cover of grazing-sensitive species over the monitored period. Diversity parameters, of especially the annual component, were strongly related to rainfall. A directional change, which supports the equilibrium concept, was evident in changes in perennial species composition over time. The annual component, however, showed no directional change, but displayed eventdriven, non-equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall.