Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional‐scale and local‐scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one‐season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional‐scale and local‐scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot‐level variation was contingent on pasture‐level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture‐level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture‐level temperature and grazing relationships with annual grass abundance are complex and context dependent, although the causality of this relationship deserves further examination. At the plot‐level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture‐level and plot‐level favorability interacted: perennial grasses had a higher plot‐level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross‐scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world.

中文翻译：

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跨尺度分析揭示了北部大盆地牧场年度和常年覆盖的相互作用预测因素

一年一度的外来草类入侵对北美西部的山艾树生态系统的完整性构成了广泛的威胁。尽管已经确定了年度牧草流行率和本地多年生植被的许多预测因子，但区域尺度和局部尺度预测因子如何相互作用以确定植被异质性，以及植被和牛放牧之间的关联如何随环境背景而变化，仍然存在很大的不确定性。在这里，我们对俄勒冈州和爱达荷州的烧毁和未烧毁、放牧的公共土地进行了区域范围内的单季实地调查，并根据牧场内的坡向和与水的距离进行分层，以捕捉环境背景和放牧强度的变化。我们分析了一年生草、多年生草和灌木覆盖的区域尺度和地方尺度模式，并研究了地块水平变化在多大程度上取决于牧场水平对地点有利性的预测。一年生草在烧毁和未烧毁的地点都广泛分布，这与一年生草依赖火的假设相反，并且在海拔较低和温度较高的地区以及当地较温暖的山坡上更为常见。牧场放牧压力与温度相互作用，在较高温度下，年草覆盖率与放牧压力呈正相关，但在较低温度下，与放牧压力呈负相关。这表明牧场温度和放牧与年草丰富度的关系是复杂的并且依赖于环境，尽管这种关系的因果关系值得进一步研究。在牧场内的地块水平上，年度草地覆盖率不随放牧指标变化，但多年生覆盖率却随放牧指标变化。例如，多年生草类靠近水源的覆盖率较低，但牧场内粪便数量较高时覆盖率较高，这表明对这两种放牧指标的解释存在差异。对于生态系统对温度变化的响应的预测来说，重要的是，我们发现牧场水平和地块水平的有利性是相互作用的：多年生草在较冷的山坡上具有更高的地块覆盖率，并且这种跨地形的差异在不利于生长的牧场中最为明显。地区性多年生草本植物。了解这些日益入侵的生态系统中植被对放牧的跨尺度相互作用和偶然反应背后的机制对于不断变化的世界中的土地管理至关重要。