Abstract A major challenge in rangeland ecology is understanding diverse responses of diversity to grazing, what factors determine these responses and what their relative importance is. Numerous site-level studies have explored grazing-diversity relations, but meta-analyses of these empirical results at a global scale are scarce. Our goals were to estimate the mean effect of grazing on plant richness and to assess the relative importance of different variables at a global scale. We conducted a global meta-analysis of 259 comparisons of plant richness in grazed vs. ungrazed sites from 96 published studies. Then, we performed analyses of subgroup, meta-regression and correlation for testing the relative roles of regional and local variables (e.g. evolutionary history of grazing, aridity, stocking rate, etc.). Globally, grazing significantly increased plant richness compared to grazing exclusion, especially in wet grasslands. The effect of evolutionary history of grazing was insignificant, which cannot support the major perception behind Milchunas-Sala-Lauenroth (MSL) model. Aridity, vegetation type, and stocking rate were three important variables that together explained 41 % of the global variation in plant richness. The roles of stocking rate and duration of grazing exclusion were revealed only when aridity and vegetation type were added to the analyses, which showed a stronger effect of stocking rate in wet areas but a stronger effect of the duration of grazing exclusion in dry areas. Changes in plant richness were significantly correlated with changes in soil carbon and nitrogen, both showing hump-shaped patterns. Our findings substantiate that scholars may improve existing theories (e.g. the MSL model, the intermediate disturbance hypothesis) through further expounding the interactions between grazing variables and aridity and vegetation type. Rangeland managers need to devise local-scale grazing strategies for conserving plant diversity according to site-specific conditions, rather than adopting a one-size-fits-all solution.

中文翻译：

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放牧对植物丰富度影响的全球荟萃分析

摘要 牧场生态学的一个主要挑战是了解多样性对放牧的不同反应、决定这些反应的因素以及它们的相对重要性。许多站点级研究探索了放牧-多样性关系，但在全球范围内对这些经验结果的元分析很少。我们的目标是估计放牧对植物丰富度的平均影响，并在全球范围内评估不同变量的相对重要性。我们对来自 96 项已发表研究的 259 项放牧与未放牧地点植物丰富度的比较进行了全球荟萃分析。然后，我们对亚组、元回归和相关性进行了分析，以测试区域和局部变量（例如放牧的进化历史、干旱、放养率等）的相对作用。在全球范围内，与不放牧相比，放牧显着增加了植物丰富度，尤其是在潮湿的草原上。放牧进化史的影响微不足道，不能支持 Milchunas-Sala-Lauenroth (MSL) 模型背后的主要看法。干旱、植被类型和放养率是三个重要的变量，它们共同解释了全球植物丰富度变化的 41%。放牧率和禁牧持续时间的作用只有在将干旱和植被类型加入分析时才显示出来，表明在潮湿地区放牧率的影响更强，而在干旱地区放牧禁牧持续时间的影响更强。植物丰富度的变化与土壤碳和氮的变化显着相关，均呈驼峰状。我们的研究结果证实，学者们可以通过进一步阐述放牧变量与干旱和植被类型之间的相互作用来改进现有的理论（如 MSL 模型、中间扰动假说）。牧场管理者需要根据特定地点的条件设计本地规模的放牧策略来保护植物多样性，而不是采用一刀切的解决方案。