Twenty years of rest returns grazing potential, but not palatable plant diversity, to Karoo rangeland, South Africa

Seymour, C. L., et al., 2010. Journal of Applied Ecology

Original research (primary data)
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P>1. Up to 73% of the world’s rangelands are degraded, and increasing demand for meat in developing countries and a growing human population are likely to exert even greater pressures on rangelands in the next 20-50 years. Restoration of rangeland grazing potential and resilience is therefore important, particularly in the face of climate change. 2. We investigated the influence of past stocking rates (from 1910 to 1987), rainfall, and current grazing regimes (from 1988 to 2008) on plant assemblages, grazing potential, and diversity of palatable species in southern Karoo rangelands, South Africa. 3. We used herbivore exclusion experiments to test whether resting rangeland for 20 years enables recovery of plant assemblages (where seed sources are present within 50 m), regardless of previous grazing history. Mean annual rainfall over this period was 15% higher than the mean annual rainfall for the preceding 80 years and included two exceptionally wet years. 4. While rainfall was a primary driver of total vegetation cover, grazing history explained differences in plant species composition: plots with shared historical grazing intensity were more similar than plots with the same grazing regimes between 1988 and 2008. 5. In historically heavily-grazed exclusion plots, cover of the palatable species Tripteris sinuata (formerly Osteospermum sinuatum) returned to levels comparable to that in both exclusion and lightly-grazed plots with a moderate grazing history. Five palatable species (Pteronia empetrifolia, Tetragonia spicata, Berkheya spinosa, Hereroa latipetala and Ruschia spinosa) failed to re-establish, however, despite the presence of seed-producing plants nearby. Furthermore, only cover of P. empetrifolia increased significantly in historically moderately-grazed plots. Cover of unpalatable plants (e.g. Pteronia pallens) increased in all plots over time. 6.Synthesis and applications. These findings suggest that present species composition of arid shrublands reflects historical management at time scales greater than 20 years. Despite high rainfall enabling the return of grazing potential through recovery of a single forage species, rest alone did not ensure the return of all palatable species, with implications for rangeland resilience. Restoring the full suite of palatable species over management timeframes will require more complex interventions such as reseeding or selective clearing.

Case studies

Basic information

  • Case ID: INT-136-1
  • Intervention type: Combination
  • Intervention description:

    grazing exclosures

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Loss of food production  Positive rate of increase in % vegetation cover of palatable species; final % cover
  • Approach implemented in the field: Yes
  • Specific location:

    the Sandrivier valley (33°10¢S, 22°17¢E, 800 m altitude) of the southern Great Karoo on the adjacent sheep ranches of ‘Argentina’ and ‘Tierberg’

  • Country: South Africa
  • Habitat/Biome type: Tropical and subtropical grasslands |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: Effectiveness determined by comparing to control plots where grazing had been allowed to continue throughout the study period. The intervention either had a positive effect or no effect therefore coded as positive For the palatable species Tripteris sinuata: "Model selection using AIC selected our hypothesis (‘hypothesized model’) that moderately-grazed treatments would have a slower rate of increase than historically heavily-grazed exclusion plots, but that cover in historically heavily-grazed plots that continued to be grazed by sheep had increased slower than all other treatments, as the best model" ... "percentage cover of Tripteris sinu- ata in 2008 showed that only the historically heavily-grazed site that had continued to be grazed by sheep between 1988 and 2008 had a significantly lower percentage cover (Kruskal– Wallis One-way anova Chi-square = 9Æ67, P = 0Æ046, n = 5; Multiple comparisons with t-distributions), whilst the exclu- sion treatment plot on the historically heavily-grazed site was not significantly different to the historically moderately-grazed sites for all current grazing treatments." For other palatable species: "A comparison of average percentage cover in exclusion plots between 1988 and 2008 of four other palatable species (Tetra- gonia spicata, Berkheya spinosa, Hereroa latipetala, Ruschia spinosa) on the farm with a history of heavy grazing showed that 20 years of rest did not result in any significant change in percentage cover, which remained close to zero for all four spe- cies. " "Despite the contribution of T. sinuata in restoring the grazing potential of the rangeland to previous levels, certain palatable species (Pteronia empetrifolia, Tetragonia spicata, Berkheya spinosa, Hereroa latipetala and Ruschia spinosa) did not increase or establish at all in historically heavily-grazed plots, and showed no appreciable increase in cover in moderately- grazed rangelands, despite rainfall over the two decades of the experiment exceeding the long-term mean by 15%." --> therefore also no effect on diversity of palatable species
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic: