PS 76-181
Resistance and resilience of native serpentine community species to invasion by barbed goatgrass
Many managers target the removal of invasive species to promote local species diversity. However, eradication seldom produces complete native recovery and often facilitates increased dominance of other exotics. A first critical step toward more complete restoration is to understand what traits enable some species to profit from invader removal more than others. We examined the role of functional traits and pre-invasion commonness in resistance (maintenance of high relative abundance under invader dominance) and resilience (proliferation after invader removal) of individual species in an annual serpentine grassland. We hypothesized that species with stress tolerant traits (low SLA, low foliar nitrogen content, short stature, and low leaf water content) would better tolerate lower resource availability under invasion and therefore maintain higher resistance. We hypothesized species with faster growth (high sla, foliar nitrogen content, and leaf water content) would sport greater resilience due to increased colonization ability. To quantify resistance, we visually estimated cover of all species in 75 matched paired invaded and non-invaded plots. To quantify resilience, we performed the same community sampling in invaded plots treated with herbicide and untreated plots. We obtained trait values for each species from an existing local database. We then performed linear model selection to determine which functional traits best predicted resistance (cover in invaded plots / cover in uninvaded plots) and resilience (cover in recovered plots / cover in invaded plots).
Results/Conclusions
In common species (those occurring in more than 10% of plots), resistance to invasion was positively correlated with foliar nitrogen content (p=.02, r^2 =.12) whereas resilience to invasion was negatively correlated with height (p<0.05). There was no significant relationship between functional traits and resistance or resilience of rare species to invasion (p>0.05). Our results contradict earlier findings that rare species are insulated from negative impacts of invaders; instead we found selection for fast-growing species common species under invasion and slow-growing species after invasion.