Influence of grazing intensity on phylogenetic and CSR plant strategy diversity of species-rich grasslands, Mazandaran, Iran

Abstract

Abstract Recently more studies have been made to predict plant response to livestock grazing using plant functional traits that can be used as effective indicators to study the adaptation of species under grazing disturbances. Here, we test the responses of different plant diversity (taxonomic, phylogenetic and functional diversity) and strategies (Competitive, stress tolerant, and ruderal) in order to grazing intensity. This study was carried out in Siah Bisheh Rangelands, located in the extreme southeast of Mazandaran province, Iran. In the study area, three sites were selected in an area subjected to low and high grazing intensity (LG and HG, respectively), totaling 6 sites. In each site and condition of grazing intensity, 3 transects of 100 meters were randomly placed, and along each transect, 5 plots (1×1 m2) were sampled at 20 m intervals, totaling 45 m2 per grazing intensity. In each plot, the plant’s crown cover was recorded. To access the evolutionary relationship among species, we generate a phylogenetic tree for the plant communities in the two grazing intensities (76 and 66 species in LG and HG, respectively). In order to estimate plant strategy and functional diversity in different types of rangeland, A competitive, stress tolerant, and ruderal (CSR) plant strategy scheme was applied based on key leaf traits: leaf area (LA), leaf dry matter content (LDMC) and specific leaf area (SLA). Based on the results, higher grazing intensity led to the shift from the ruderal strategy to the stress-tolerance strategy, both at the species level and plot community weighted mean (CWM) traits. Also, higher grazing intensity significantly reduces species richness and diversity but increases the functional divergence evenness and CWM of LDMC. Finally, stress-tolerant and ruderal strategies dominated under high and low grazing intensities, respectively. Our studied results suggest the vital role of plant functional traits in assessing plant strategies.