Water as the key to sagebrush restoration success in cheatgrass-invaded ecosystems

Restoration treatments in Bromus tectorum (cheatgrass)-invaded sagebrush habitat have often produced poor results. This is perhaps due to multifaceted ecological changes associated with cheatgrass invasion like reduced water availability, altered nutrient availability, and shifts in soil microbial communities. We tested whether suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes improved restoration success. We conducted field experiments in Idaho, Utah, and Arizona where we transplanted seedlings of Artemisia tridentata ssp. tridentata (basin big sagebrush) and Elymus elymoides (squirreltail). Growth and survivorship of both species were higher in sites with greater precipitation and lower cheatgrass abundance. Significant nutrient modification effects were seen in Utah, where cheatgrass abundance was highest and soil nutrients were most limiting. In Utah, we observed an increase of 14% in survivorship for squirreltail in response to carbon addition, and 119% increase in growth of sagebrush with phosphorus addition. Inoculating plants with sagebrush rhizosphere soil or a commercial arbuscular mycorrhiza at the time of planting did not significantly affect growth, survivorship, arbuscular mycorrhizal fungi colonization, or extraradical mycorrhizal hyphae length for either plant species. The largest effects on seedling growth (+384%) and survivorship (+262%) were observed in response to the suppression of cheatgrass using a weed barrier cloth and associated with increased water availability. Interactions between suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes were not significant. Direct reduction of cheatgrass was shown to be more effective than targeting soil legacy effects associated with cheatgrass with regards to restoration outplanting success.