Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 13, 2014
Publication Date: May 1, 2014
Citation: Hirsch, M.C., Monaco, T.A., Call, C.A., Sheley, R.L. 2014. Large-scale downy brome treatments alter plant-soil relationships and promote perennial grasses in salt desert shrublands. Rangeland Ecology and Management. 67:255-265. Interpretive Summary: Invasive plant species pose a major threat in ecosystems and complicate managerial efforts to improve wildlife habitat, forage productivity, and reduce wildfire risk. After initial colonization and spread of invasive plants, their impact and dominance may increase with time, depending on their functional distinctiveness within the ecosystem (Mack et al. 2000, Strayer et al. 2006). At this point, ecosystem processes are largely controlled by the invasive species (MacDougal and Turkington 2005), including plant-soil resource dynamics and disturbance regimes (D'Antonio and Vitousek 1992, Ehenfeld et al. 2005). Moreover, when these processes are primarily driven by invasive species, in the absence of functionally diverse perennial species, a perpetual feedback cycle is developed that modifies natural successional pathways (Kulmatiski et al. 2008, Beckage et al. 2009). Consequently, there is great need to understand plant-soil relationships of invasive-plant-impacted ecosystems and explore how rehabilitation actions influence these relationships.
Technical Abstract: The interrelationship between invasive annual grass abundance and soil resource availability varies spatially and temporally within ecosystems and may be altered by land treatments. We evaluated these relationships in two salt desert landscapes where the local abundance of Bromus tectorum L. (downy brome) was highly variable and increased more than 12-fold over a three-year period. During this period, we measured how this relationship was impacted by factorial combinations of prescribed burning, pre-emergence herbicide application, and biomass removal at large scales typical of realistic land management in the Great Basin. In the first year when abundance was lowest, B. tectorum cover was negatively correlated with spring measurements of soil H2O and NO3-N. In the two years following treatment, burning and herbicide applications, especially when combined, significantly (P<0.1) reduced cover of B. tectorum, which in turn significantly (P<0.1) increased soil NO3-N accumulation in the spring. Our study demonstrates that B. tectorum directly controls these soil resources and that treatments designed to reduce its abundance simultaneously increase soil resource availability in impoverished salt desert shrub ecosystem. Thus, altering this plant-soil relationship to yield restoration opportunities must comprise more than merely reducing B. tectorum abundance but include tactics that facilitate resource utilization by the residual plant community or successfully establish plant species capable of resource acquisition in the spring.