Grazing intensity enhances spatial aggregation of dominant species in a desert steppe

Abstract Understanding how grazing activity drives plant community structure or the distribution of specific species in a community remains a major challenge in community ecology. The patchiness or spatial aggregation of specific species can be quantified by analyzing their relative coordinates in the community. Using variance and geostatistical analysis methods, we examined the quantitative characteristics and spatial distribution of Stipa breviflora in a desert steppe in northern China under four different grazing intensities (no grazing, NG, light grazing, LG, moderate grazing, MG, and heavy grazing, HG) at three small spatial scales (10 × 10 cm, 20 × 20 cm, 25 × 25 cm). We found that grazing significantly increased cover, density, and proportion in standing crop of S. breviflora, but decreased height. The spatial distribution of S. breviflora was strongly dependent upon the sampling unit and grazing intensity. The patchiness of S. breviflora reduced with sampling scale, and spatial distribution of S. breviflora was mainly determined by structural factors. The intact clusters of S. breviflora were more fragmented with increasing grazing intensity and offspring clusters spread out from the center of the parent plant. These findings suggest that spatial aggregation can enhance the ability of S. breviflora to tolerate grazing and that smaller isolated clusters are beneficial to the survival of this dominant species under heavy grazing

Understanding Grassland Degradation and Restoration from the Perspective of Ecosystem Services: A Case Study of the Xilin River Basin in Inner Mongolia, China

Ecosystem services (ESs) and their transformations in northern China play a crucial role in regional sustainability. During the past several decades, grassland degradation has become one of the most important ecological and economic issues in this region. Therefore, understanding the impacts of grassland degradation and restoration on ESs is essential for maintaining ecological resilience and social security of Northern China. Our objective was to explore the relationship between ESs and grassland changes induced by vegetation succession in the Xilin River Basin, Inner Mongolia, China. Using vegetation maps derived from remotely sensed imagery collected in 1983, 1989, 2000, and 2011, we calculated the degree of grassland degradation using the Grassland Degradation Index (GDI). Aboveground biomass (AGB), soil conservation (SC), and water retention (WR) were also estimated to assess ESs for each year. Our results show that: (1) GDI increased during 1983–2000 and decreased during 2000–2011 indicating that after experiencing two decades of severe degradation the grassland has been restored since 2000. (2) AGB and SC were significantly negatively correlated with GDI. Changes in grassland conditions significantly affected WR and SC with both declining during 1983–2000 and increasing afterwards. The increase of SC, however, was slow compared to AGB and WR, which is an indication of time lag in soil restoration. (3) Grasslands in the middle and lower reaches experienced worse degradation than in the upper reaches. (4) AGB and SC exhibited a synergy, while trade-offs existed between AGB and WR and SC and WR. In summary, significant changes in grassland ecosystems in the Xilin River Basin over the past three decades affected the dynamics of ESs among which SC and WR require special attention in the future

Alpha, beta and gamma diversity differ in response to precipitation in the Inner Mongolia grassland.

Understanding the distribution pattern and maintenance mechanism of species diversity along environmental gradients is essential for developing biodiversity conservation strategies under environmental change. We have surveyed the species diversity at 192 vegetation sites across different steppe zones in Inner Mongolia, China. We analysed the total species diversity (γ diversity) and its composition (α diversity and β diversity) of different steppe types, and their changes along a precipitation gradient. Our results showed that (i) β diversity contributed more than α diversity to the total (γ) diversity in the Inner Mongolia grassland; the contribution of β diversity increased with precipitation, thus the species-rich (meadow steppe) grassland had greater contribution of β diversity than species-poor (desert steppe) grassland. (ii) All α, β and γ species diversity increased significantly (P<0.05) with precipitation, but their sensitivity to precipitation (diversity change per mm precipitation increase) was different between the steppe types. The sensitivity of α diversity of different steppe community types was negatively (P<0.05) correlated with mean annual precipitation, whereas the sensitivity of β and γ diversity showed no trend along the precipitation gradient (P>0.10). (iii) The α diversity increased logarithmically, while β diversity increased exponentially, with γ diversity. Our results suggest that for local species diversity patterns, the site species pool is more important in lower precipitation areas, while local ecological processes are more important in high precipitation areas. In addition, for β diversity maintenance niche processes and diffusion processes are more important in low and high precipitation areas, respectively. Our results imply that a policy of "multiple small reserves" is better than one of a "single large reserve" for conserving species diversity of a steppe ecosystem, and indicate an urgent need to develop management strategies for climate-sensitive desert steppe ecosystem

The environmental characteristics (mean annual precipitation MAP, mean annual temperature MAT, and major soil types) and species diversity composition (α, β and γ) of the seven steppe community types and of the three vegetation types in the Inner Mongolia grassland.

<p>The β diversity has two components of β nestedness diversity (β_N) and β replacement diversity (β_R). The diversity values are the mean ± s.e.m of species number recorded in ten plots at each site. The percentage of α and β diversity in γ diversity are also shown as α% and β%.</p

Species diversity of the steppe grassland in Inner Mongolia.

<p>The data are presented for seven major steppe community types: Kle (<i>Stipa klemenzii</i> desert steppe), Bre (<i>Stipa breviflora</i> desert steppe), Kry (<i>Stipa krylovii</i> typical steppe), Chi.T (<i>Leymus chinensis</i> typical steppe), Gra (<i>Stipa grandis</i> typical steppe), Bai (<i>Stipa baicalensis</i> meadow steppe), Chi.M (<i>Leymus chinensis</i> meadow steppe); three steppe vegetation types: DS (desert steppe), TS (typical steppe), MS (meadow steppe); and the Inner Mongolia grassland as a whole (IMG). A: Proportion of <i>α</i> diversity (black), <i>β</i> nestedness diversity (<i>β_N</i>) (white) and <i>β</i> replacement diversity (<i>β_R</i>) (grey) in <i>γ</i> diversity; B: The trend of the proportion of <i>α</i> diversity (black dot), <i>β_N</i> diversity (white dot) and <i>β_R</i> diversity (grey dot) in <i>γ</i> diversity in the seven grassland types with the types ordered according to the annual mean precipitation of their distribution areas, with precipitation increase from left to right.</p

Map of the study region, showing the vegetation zones and sampling sites.

<p>Map of the study region, showing the vegetation zones and sampling sites.</p