Understanding changes in the plant community due to removal of invasive species requires addressing not only taxonomic species composition but also ecosystem functioning via traits of individual plants, particularly in systems with novel interactions. This research explores how treatment of an invasive riparian shrub (Tamarix spp.) impacts functioning of the surrounding plant community, specifically habitat for the endangered Southwestern willow flycatcher (Empidonax traillii extimus, abbr. SWFL), a native bird which readily nests in Tamarix. SWFL nesting habitat is associated with specific tree branching structures (a functional trait) and presence of water, not the presence of any particular species; it is as yet unknown whether restoration activities are producing such conditions. Our research asks: Which abiotic environmental characteristics of formerly Tamarix-dominated sites predict functional traits of plants? To answer this question, we sampled specific leaf area (SLA; a trait correlated with several aspects of functional niche) and branching density of Tamarix at 34 sites in Grand County, UT. Soil samples and geographic data were also collected at these sites, and plant community surveys were conducted.
Results/Conclusions
We found high variability in both SLA and vertical biomass distribution among both sites and reaches, as well as highly different results from literature values taken at other locations. None of the environmental variables explained SLA, suggesting a possible role of genetic variation. However, we also found a significant negative effect of soil electrical conductivity and significant positive effects of river width and herbivory level on overall branching density, demonstrating that abiotic factors can partially explain intraspecific variation. Our results can predict factors influencing desirable traits post-restoration, which will continue to be of high importance for the SWFL and ecosystem management in affected areas.