Livestock grazing is a globally important land use and has the potential to significantly influence plant community structure and ecosystem function, yet several critical knowledge gaps remain on the direction and magnitude of grazing impacts. Furthermore, much of our understanding of the long-term effects on plant community composition and structure are based on grazer exclusion experiments, which explicitly avoid characterizing effects along grazing intensity gradients. We sampled big sagebrush plant communities using 68 plots located along grazing intensity gradients to determine how grazing intensity influences multiple aspects of plant community structure over time. This was accomplished by sampling plant communities at different distances from 17 artificial watering sources, using distance from water and cow dung density as proxies for grazing intensity at individual plots. Total vegetation cover and total grass cover were negatively related to grazing intensity, and cover of annual forbs, exotic cover, and exotic richness were positively related to grazing intensity. In contrast, species richness and composition, bunchgrass biomass, shrub density and size, percentage cover of bare ground, litter, and biological soil crusts did not vary along our grazing intensity gradients, in spite of our expectations to the contrary. Our results suggest that the effects of livestock grazing over multiple decades (mean = 46 years) in our sites are relatively small, especially for native perennial species, and that the big sagebrush plant communities we sampled are somewhat resistant to livestock grazing. Collectively, our findings are consistent with existing evidence that indicates the stability of the big sagebrush plant functional type composition under current grazing management regimes.

中文翻译：

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牲畜放牧集约化对旱地植物群落多样性、丰度和组成的小影响

畜牧业放牧是一种全球重要的土地利用方式，有可能显着影响植物群落结构和生态系统功能，但在放牧影响的方向和程度方面仍存在一些关键的知识空白。此外，我们对植物群落组成和结构的长期影响的大部分理解都是基于食草动物排除实验，这些实验明确避免了沿放牧强度梯度表征影响。我们使用沿放牧强度梯度分布的 68 个地块对大型山艾树植物群落进行采样，以确定放牧强度如何随时间影响植物群落结构的多个方面。这是通过对距离 17 个人工水源不同距离的植物群落进行采样来实现的，使用与水的距离和牛粪密度作为各个地块放牧强度的代表。植被总盖度和草地总盖度与放牧强度呈负相关，一年生杂草盖度、外来覆盖和外来丰富度与放牧强度呈正相关。相比之下，物种丰富度和组成、束草生物量、灌木密度和大小、裸地覆盖率、枯枝落叶和生物土壤结皮并没有随着我们的放牧强度梯度而变化，尽管我们的预期恰恰相反。我们的结果表明，几十年来（平均 = 46 年）牲畜放牧对我们场地的影响相对较小，尤其是对本地多年生物种而言，而且我们采样的大型山艾树植物群落对牲畜放牧有一定抵抗力。总的来说，