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Kirk DA, Goldsmith FB.2018. Grazing pressure versus environmental covariates: Effects on woody and herbaceous plant biodiversity on a limestone mountain in northern Tunisia. PeerJ Preprints6:e27089v1https://doi.org/10.7287/peerj.preprints.27089v1
Mediterranean vegetation is characterized by high biodiversity and conservation value and grazing is controversial. We sampled woody and herbaceous plants on a limestone mountain with strong mesic-xeric gradients, ranked grazing pressure (on a scale of 1-4) and asked whether grazing had a significant effect on plant compositional abundance before and after controlling for environmental covariates. For woody species the shift in means among grazing classes was greater than for herbaceous species according to distance-based redundancy analysis (dbRDA). For herbaceous species differences in multivariate dispersion were greater among grazing classes. Both groups showed significant differences among grazing classes in multivariate location (permutational multivariate ANOVA), even after controlling for aspect. After taking into account biophysical covariates, grazing was not significant and the variation unique to grazing was small. According to best models in dbRDA, grazing was significant in two models for woody species, and all models for herbaceous species. For woody species, spatial variables were most important and confounded with grazing while for herbs, altitude, distance to road, slope, rock outcropping were important. Significant effects of grazing were found for forbs, Poaceae, and Geophytes but not woody and herbaceous legumes. We found a negative relationship between grazing intensity and beta diversity for herbs overall and especially Poaceae, but moderate grazing resulted in higher beta diversity for Geophytes and herbaceous legumes. Jebel Ichkeul provides a microcosm of similar conservation and management issues elsewhere in the Mediterranean. Carefully controlled grazing may enhance plant diversity and maintain the characteristics of maquis vegetation.
A. Bubble plot of relative proportions of Pistachia lentiscus in non-metric multidimensional scaling ordination diagram based on 78 quadrats at Jebel Ichkeul. Keys shows proportional occurrence at each site and grazing index. B. Bubble plot
Mean values for environmental covariates under different grazing regimes: altitude (m a.s.l.) and distances (m) to roads, farms, urban nuclei and streams. Bars shown mean ± SE. Different letters above the bars indicate signiﬁcant differences (one-way perm
Mean values for species richness and Shannon-diversity indices under different grazing regimes. Bars shown mean ± SE. Different letters above the bars indicate signiﬁcant differences (one-way permutational multivariate ANOVA, 9999 permutations; pair-wise