Disturbance, dominance & disaster: Heavyweights in structuring herbaceous savanna communities.

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Dave Thompson

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Alterations of historic disturbances are pervasive in their impacts on vegetation. This is especially relevant in managed grasslands sensu lato, where often only depauperate herbivore suites persist. Annual (from 2006) monitoring of herbaceous vegetation in the savannas of the Kruger National Park (KNP), South Africa, revealed that ten years of herbivore exclusion had no effect on plant richness, and little effect on dominance. To examine more widely the thesis that grazing impacts richness via its effects on plant dominance, we conducted a meta-level analysis comparing results from 252 grazing exclosure experiments globally. Contrary to prevailing theory, we found that the effect of grazing on richness is negatively correlated to the effect of grazing on dominance, and not to MAP. In 2015/16 KNP experienced one of its worst droughts on record. For the decade prior to this, sampling plots were dominated by a single herbivory-resistant, unpalatable grass species. We built on this finding to explore the impact of extreme disturbance on these herbaceous plant communities. In the first two years post-drought (2017/18), the community dominance shifted to palatable grasses and forbs, with a simultaneous increase in plant diversity. This was seen in both grazed and ungrazed plots. The drought, with severe negative short-term impacts, transformed the savanna, potentially increasing available herbivore forage and biodiversity in the long-term. The positive, unexpected impact of drought supports the notion that large disturbances can enhance habitats, and that restoration efforts need not focus only on replicating pre-disturbance ecosystems.

Resource Type:
Audio/Video, Conference Presentation, SER2019

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Society for Ecological Restoration