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JOURNAL OF ARID ENVIRONMENTS, vol.73, no.12, pp.1149-1157, 2009 (SCI-Expanded)
In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are patterns in examined vegetation; how dominant species contribute to these patterns; and how patterns differ between grazed and ungrazed vegetation. We determined that protection from grazing increased species richness. Grazing significantly changed composition through decreasing total plant, forb, grass and E valesiaca covers, while substantially increasing T sipyleus cover. Topography, soil and grazing appear to impact the dominance of plant communities where F valesiaca and T sipyleus prevail. These two dominant species had a significant effect in shaping vegetation patterns. Based on regression analysis, alterations in species richness with changes in cover of forbs and shrubs were evident, and spatial heterogeneity of F. valesiaca and T sipyleus indicated unstable vegetative patterns in heavily grazed pastures and successional changes in protected pastures. Our study results identify E valesiaca and T sipyleus as indicator species of vegetation suppression in condition assessments of degraded steppe rangelands. Published by Elsevier Ltd.