Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2010
Publication Date: 3/1/2011
Publication URL: http://hdl.handle.net/10113/49470
Citation: James, J.J., Drenovsky, R.E., Monaco, T.A., Rinella, M.J. 2011. Managing soil nitrogen to restore annual grass infested plant communities: an effective strategy or incomplete framework? Ecological Applications. 21(2):490-502. Interpretive Summary: Increases in soil nitrogen following disturbance facilitates the spread of weeds so most management assumes decreasing nitrogen will help restore weed invaded systems. Soil nitrogen management is a difficult and costly practice and there is no quantitative synthesis evaluating its effectiveness. We quantitatively evaluated the impact of this practice on the performance of invasive annual grasses and native perennial grasses. The analysis suggested soil nitrogen management will be effective if there are opportunities for natives to first establish without competition from weeds but will likely be ineffective if a significant number of weed seeds are present
Technical Abstract: Theoretical and empirical work has established a positive relationship between resource availability and habitat invasibility. For invasive annual grasses, similar to other invasive species, invader success has been most often tied to increases in nitrogen (N) availability. These observations have lead to the logical assumption that managing soils for low N availability will facilitate restoration of invasive plant dominated systems. Although invasive annual grasses pose a serious threat to a number of perennial-dominated ecosystems worldwide, there has been no quantitative synthesis evaluating the degree to which soil N management may facilitate restoration efforts. Our first objective was to use meta-analysis to evaluate effects of soil N management on growth rate, biomass, tiller production and competitive interactions between invasive annual and native perennial grass seedlings. Our second objective was to link our results to current theories of plant ecological strategies and community assembly to improve our ability to understand how soil N management may be used to restore annual grass dominated communities. Annual grasses maintained higher growth rates and greater biomass and tiller production under low and high N availability. We found no evidence that lowering N availability fundamentally alters competitive interactions between annual and perennial grass seedlings. In the majority of studies, competitive effects of annual neighbors on perennial target plants were similar under low and high N availability. In situations where competitive effects of neighbors on target plants decreased when N availability was lowered, this decrease was similar regardless of neighbor or target plant identity. Moreover, our analysis showed perennial plants grown under competition in high N soils produced more biomass than perennial plants grown under competition in low N soils. While these findings counter many of the initial restoration and soil N management assumptions, these results are consistent with current understanding of traits driving variation in plant ecological strategies and processes associated with community assembly. We argue that in restoration scenarios in which the native plant community is being reassembled from seed, soil N management will have no direct positive effect on restoration outcomes unless invasive plant propagule pools and priority effects are controlled the first growing season.