Summary1. Ecosystem invasibility is determined by combinations of environmental variables, invader attributes, disturbance regimes, competitive abilities of resident species and evolutionary history between residents and disturbance regimes. Understanding the relative importance of each factor is critical to limiting future invasions and restoring ecosystems. 2. We investigated factors potentially controlling Bromus tectorum invasions into Artemisia tridentata ssp. wyomingensis communities across 75 sites in the Great Basin. We measured soil texture, cattle grazing intensity, gaps among perennial plants and plant cover including B. tectorum, biological soil crusts (BSCs) and bare soil. Using a priori knowledge, we developed a multivariate hypothesis of the susceptibility of Artemisia ecosystems to B. tectorum invasion and used the model to assess the relative importance of the factors driving the magnitude of such invasions. 3. Model results imply that bunchgrass community structure, abundance and composition, along with BSC cover, play important roles in controlling B. tectorum dominance. Evidence suggests abundant bunchgrasses limit invasions by limiting the size and connectivity of gaps between vegetation, and BSCs appear to limit invasions within gaps. Results also suggest that cattle grazing reduces invasion resistance by decreasing bunchgrass abundance, shifting bunchgrass composition, and thereby increasing connectivity of gaps between perennial plants while trampling further reduces resistance by reducing BSC. 4. Synthesis and applications. Grazing exacerbates Bromus tectorum dominance in one of North America's most endangered ecosystems by adversely impacting key mechanisms mediating resistance to invasion. If the goal is to conserve and restore resistance of these systems, managers should consider maintaining or restoring: (i) high bunchgrass cover and structure characterized by spatially dispersed bunchgrasses and small gaps between them; (ii) a diverse assemblage of bunchgrass species to maximize competitive interactions with B. tectorum in time and space; and (iii) biological soil crusts to limit B. tectorum establishment. Passive restoration by reducing cumulative cattle grazing may be one of the most effective means of achieving these three goals.

Agriculture and Natural Resources, Browns Valley, CA 95918, USA Summary 1. Seeding native plants is a key management practice to counter land degradation across the globe, yet the majority of seeding efforts fail, limiting our ability to accelerate ecosystem recovery. 2. Recruitment requires transitions through several seed and seedling stages, some of which may have overriding influences on restoration outcomes. We lack, however, a general framework to understand and predict differences in these critical demographic processes across species. Functional traits influence fitness, and consequently, trait variation could provide the basis for a framework to explain and predict variation in life stage transition probabilities. 3. We used seed and seedling traits, and field probabilities of germination, emergence, seedling establishment, and survival for 47 varieties of drylands grasses under two watering treatments to identify critical life stage transitions and quantify the effect of traits on cumulative survival through the first growing season. 4. Variation in germination and emergence probabilities explained over 90% of the variation in cumulative survival regardless of seedling survival probabilities or watering treatment, with emergence probability being the strongest predictor of cumulative survival. 5. Coleoptile tissue density and seed mass had significant effects on emergence and germination, respectively, explaining 10-23% of the variation in transition probabilities. 6. Synthesis and applications. While the majority of functional trait work has centred on linking leaf and root traits to resource acquisition and utilization, our study demonstrates that traits associated with germination and emergence may have prevailing influences on restoration outcomes. A portion of these traits have been examined, but there is substantial opportunity to identify other key traits driving these demographic processes. These advancements will underpin our ability to develop trait-based frameworks for overcoming recruitment barriers and facilitating recovery of degraded systems across the globe.

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The Sagebrush Steppe Treatment Evaluation Project (SageSTEP) is a comprehensive, integrated, long-term study that evaluates the ecological effects of fire and fire surrogate treatments designed to reduce fuel and to restore sagebrush (Artemisia spp.) communities of the Great Basin and surrounding areas. SageSTEP has several features that make it ideal for testing hypotheses from state-and-transition theory: it is long-term, experimental, multisite, and multivariate, and treatments are applied across condition gradients, allowing for potential identification of biotic thresholds. The project will determine the conditions under which sagebrush steppe ecological communities recover on their own following fuel treatment versus the communities crossing ecological thresholds, which requires expensive active restoration.