Invasion of non-native annual grasses is a significant threat to the sustainability of sagebrush steppe ecosystems. Ecological resilience, the ability to bounce back after a disturbance, and resistance, the ability to withstand invasion, are influenced by both abiotic factors, such as soil temperature, moisture, elevation, and aspect, and biotic factors, such as plant community composition. We quantified the effects of moss biocrusts, native shrubs, and native perennial grasses on invasion resistance in a greenhouse experiment containing dominant sagebrush ecosystem plants and invasive grasses. We saw greatest suppression of invasive annual grass biomass in treatment replicates containing native bunchgrass species (P < 0.01). Final invasive grass biomass was 4.79 g on average when perennial grasses were not present and was reduced to 1.59 g with perennial grass competition (P < 0.01). Presence of shrubs and moss biocrusts did not decrease annual grass biomass (P = 0.38 and P = 0.25, respectively). We saw complex interactions between native plants grown in these ideal greenhouse conditions such that native perennial grass seedlings grown with sagebrush seedlings had a mean of 4.50 g more biomass (P < 0.001) relative to pots grown with bitterbrush or without shrubs, but shrubs were an average of 7.9 cm (P < 0.001) shorter and had biomass 4.75 g lower (P < 0.001) in pots grown with perennial grasses compared with shrubs grown without perennial grasses. Our results demonstrate that with increased treatment complexity, we see greater invasion resistance, but that nuanced relationships between plant community members should also be considered in managing and restoring these imperiled ecosystems.

非本地一年生草本植物的入侵对山艾树草原生态系统的可持续性构成重大威胁。生态恢复力（干扰后恢复的能力）和抵抗力（抵御入侵的能力）受到非生物因素（如土壤温度、湿度、海拔和坡向）和生物因素（如植物群落组成）的影响。我们在包含优势山艾生态系统植物和入侵草的温室实验中量化了苔藓生物结皮、本地灌木和本地多年生草对入侵抵抗力的影响。我们发现，在含有本地束草物种的处理重复中，入侵性一年生草生物量受到最大程度的抑制（P < 0.01）。当多年生草不存在时，最终入侵草生物量平均为 4.79 克，随着多年生草竞争，最终入侵草生物量减少至 1.59 克（P < 0.01）。灌木和苔藓生物结皮的存在并没有降低年草生物量（分别为P  = 0.38 和P  = 0.25）。我们看到在这些理想的温室条件下生长的本地植物之间存在复杂的相互作用，例如，与使用苦艾树幼苗生长的本地多年生草苗相比，使用苦艾树幼苗生长的本地多年生草苗的生物量平均多出 4.50 克（P < 0.001），而盆栽中使用苦艾树或没有灌木生长，但灌木是一种与不种植多年生草的灌木相比，种植多年生草的盆栽植物平均矮 7.9 厘米（P < 0.001），生物量低 4.75 克（P < 0.001）。我们的结果表明，随着处理复杂性的增加，我们看到了更强的入侵抵抗力，但在管理和恢复这些濒危生态系统时也应考虑植物群落成员之间的微妙关系。