Long-Term Grazing Exclusion Reduces Species Diversity but Increases Community Heterogeneity in an Alpine Grassland

Shanshan Song,Zhiyao Tang,Jiangling Zhu,Zehao Shen,Chengjun Ji,Tianli Zheng,Jianxiao Zhu,Fan Zhang

doi:10.3389/fevo.2020.00066

Abstract

Extensive grazing activity is threatening the alpine grassland on the Qinghai-Tibetan Plateau. Evidence showed that grazing exclusion may change the composition, structure and functions of grassland ecosystems. However, such effects depends on the intensity and duration of exclusion. We explored the effects of short-term (2 and 4 years) and long-term (9 and 11 years) grazing exclusion on plant height, coverage and diversity and community heterogeneity in the alpine grassland on the Qinghai-Tibetan Plateau. We found no difference in plant diversity between the short-term grazing exclusion and control. However, long-term grazing exclusion reduced species richness and increased the Simpson dominance index. This decrease in plant species richness mainly contributed to the decrease in common species richness (defined as species with a relative coverage of 1~5%). In addition, community heterogeneity (coefficient of variation, CV) was significantly higher in the long-term grazing exclusion than in the controlled plots. A structural equation modeling (SEM) demonstrated that long-term grazing exclusion increased the community heterogeneity mainly by reducing species diversity. These results suggest that the effects of grazing exclusion on the composition, structure and community spatial heterogeneity of the alpine grassland ecosystem are dependent on the exclusion duration. Grazing activity may maintain high biodiversity and community stability of the alpine grassland in the harsh environment of the Qinghai-Tibetan Plateau.

Highlights

Spatial heterogeneity, or spatial variability (Kolasa and Rollo, 1991), represents the dissimilarity of community properties between multiple subplots within one survey plot (Huston, 1997; Weigelt et al, 2008)
We demonstrated that long-term grazing exclusion decreased plant diversity and productivity (Figures 1, 2), which is consistent with similar experiments in the Kobresia-dominated meadow of the Qinghai-Tibetan Plateau and the lowland grassy ecosystems of southeast Australia (Schultz et al, 2011; Wu et al, 2009)
Our results indicated that grazing exclusion, especially long-term exclusion, failed to improve grassland productivity and even reduced the community coverage and plant diversity and altered the community structure of the alpine grassland

Summary

Introduction

Spatial variability (Kolasa and Rollo, 1991), represents the dissimilarity (coefficient of variation) of community properties between multiple subplots within one survey plot (Huston, 1997; Weigelt et al, 2008). Many studies have shown that the more diverse communities have a higher probability of maintaining species and being resistant to environmental changes, i.e., more temporally stable (Tilman et al, 2006; Weigelt et al, 2008; Loreau and De Mazancourt, 2013). Little is known about how spatial variability changes under biodiversity loss. Fukami et al (2001) showed that biodiversity loss lowers ecosystem reliability (stability) between local communities by increasing the dissimilarity of species compositions, which indicates that biodiversity loss may lead to spatial heterogeneity among communities

Methods

Results

Conclusion