Effects of livestock grazing on plant species diversity vary along a climatic gradient in northeastern Iran

Abstract

Questions: (a) Do patterns of species diversity and composition differ between plots exposed to high vs. low grazing intensity? (b) Do these differences vary among three regions with different climates, representing a gradient from arid to sub-humid conditions? Location: Northeastern Iran. Methods: We compared plots intensively grazed by sheep and goat (HG) to plots with low grazing intensity (LG), across three climatic regions: arid, semi-arid and sub-humid. Species diversity (expressed as Shannon H) was compared using linear mixed-effect models. Dissimilarity analysis was used to estimate the compositional heterogeneity of different types of plots, reflecting the differences in species composition. Indicator Species Analysis was used to identify individual species associated with particular types of plots. Results: The HG plots had lower values of Shannon H than LG plots, across all climatic regions. Further, the effect of grazing on species diversity varied between the climatic regions, with the most pronounced differences between the HG and LG plots in the sub-humid region. Although no differences in species diversity were detected between the three climatic regions, compositional heterogeneity was the highest in the sub-humid region and the lowest in the semi-arid region, with the most pronounced differences between the HG and LG plots in the sub-humid region. Indicator Species Analysis showed significant main effects of both climate and grazing on species composition, revealing species that respond to grazing in each of the three climatic regions. Conclusions: Overgrazing was detected to reduce the diversity of species in all three climatic regions, even though its effect was most pronounced in the sub-humid region. Therefore, the control of overgrazing or reduction of its intensity appears an effective management tool for protecting species diversity, applicable in areas with different climates.

Impact of Grazing on Diversity of Semi-Arid Rangelands in Crete Island in the Context of Climatic Change

“…Ojima and coauthors [ 72 ] found that overgrazing results in the loss of vegetation cover and increased erosion. The low vegetation cover provides low protection from soil erosion and a high risk for degradation [ 13 ] and reduced soil porosity [ 46 , 73 ]. This reduced vegetation cover and the lower plant diversity probably increase the susceptibility of rangelands to the effects of climate change as well [ 37 , 38 , 46 ].…”

“…Heavy grazing directly changes the floristic composition of plant communities selectively, changing the structure and composition of communities at the expense of palatable species [ 43 , 44 ], and may also indirectly modify the outcome of competitive interaction by changing light availability [ 45 ]. The impact of grazing intensity on plant diversity varies along the precipitation gradient [ 46 , 47 ].…”

Species co‐occurrence shapes spatial variability in plant diversity–biomass relationships in natural rangelands under different grazing intensities

“…Substantial degradation of these valuable natural ecosystems is occurring due to overpopulation, overexploitation, and unsustainable development (United Nations Development Program, 2006). Furthermore, the unsustainable use of rangelands is being intensified by climate change (Rahmanian et al, 2020).…”

Does the intensive grazing and aridity change the relations between the dominant shrub Artemisia kopetdaghensis and plants under its canopies?

“…Grazing is a key biotic stress in dry rangelands due to its extensive application and its potential to change the community structure and species composition, and to degrade the ecosystem services (Diaz et al., 2007 ; Jankju, 2016 , Kéfi et al., 2007 ; Li et al, 2013 , Rahmanian et al, 2019 , 2020 ). Previous studies examining the herbivores as main drivers have reported that unattractive, toxic, or thorny plants may induce positive indirect (i.e., grazer‐mediated) effects on palatable herbs, shrubs, or trees (Bakker et al., 2004 ; Callaway et al., 2005 ; Smit et al., 2006 ).…”