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PeerJ. 2019 Aug 13;7:e7296. doi: 10.7717/peerj.7296. eCollection 2019.

Grazing effects on woody and herbaceous plant biodiversity on a limestone mountain in northern Tunisia.

Author information

1
Department of Geography, University College London, University of London, London, United Kingdom.
2
Current affiliation:  Aquila Conservation & Environment Consulting, Ottawa, Ontario, Canada.
3
Département de biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
4
Department of Biology, University College London, University of London, London, United Kingdom.

Abstract

Mediterranean maquis vegetation is highly biodiverse, but widespread grazing poses a challenge for management and conservation. We sampled woody and herbaceous plants separately on a limestone mountain with strong mesic-xeric gradients in Tunisia's Parc National de L'Ichkeul, assessed grazing pressure (on a scale of 1-3), and asked whether grazing had a significant effect on plant compositional abundance before and after controlling for environmental covariates. Sites on the more mesic lakeside face of the mountain were most compositionally unique, and forbs contributed most to the herbaceous beta-diversity on the mountain. We used variance partitioning to separate the collective and individual effects of the abiotic environment, grazing, human activity, and space on herbaceous and woody beta-diversity. However, the individual effect of grazing on overall plant community composition was confounded with space, due to the spatially autocorrelated grazing pressure on the mountain. Importantly, we found that herbaceous and woody communities responded differently to increasing levels of grazing intensity: herbaceous beta-diversity was highest between sites with no grazing pressure, while woody beta-diversity peaked under light grazing. Herbaceous community composition was sensitive to any intensity of grazing pressure, and biotic homogenization occured under moderate-to-high grazing pressure. On the other hand, woody community composition remained relatively similar under no to light grazing pressure, but differed under moderate-to-heavy grazing. Using a one-way permutational analysis of variance analysis, we showed that grazing had a significant effect when controlling for abiotic and spatial covariates. Our findings offer insight into the effects of grazing on maquis vegetation at Jebel Ichkeul, acting as a microcosm of similar conservation and management issues elsewhere in the Mediterranean. We suggest that a combination of monitoring and carefully controlled grazing may enhance plant diversity and maintain the region's biodiverse maquis vegetation, potentially maintaining a key climate refugium for vulnerable endemic species. Importantly, our study provides a useful baseline of the plant assemblages at Jebel Ichkeul with which to compare future vegetation changes.

KEYWORDS:

Beta diversity; Biotic homogenization; Conservation management; Goat grazing; Mediterranean maquis vegetation; North Africa

Conflict of interest statement

The authors declare there are no competing interests. However, David Anthony Kirk is Chief Executive Officer of, and owns, the ecological research consultancy, Aquila Conservation & Environment Consulting. There is no financial relationship of any kind between the submitted research and the company ‘Aquila Conservation & Environment Consulting’ or any other organization. The original fieldwork and preparation of the original thesis were funded by the Natural Environment Research Council (UK) and done at University College London in 1983.

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