Invasive plant ecosystem engineers can dramatically alter environmental variables influencing native communities. Following eradication of the engineer, systems may be slow to recover their pre-invasion state. Active replanting of native species can more quickly restore physical habitat for species of management concern, including birds and small mammals, but may also hasten the return of other pre-invasion conditions. Therefore, we explored the effects of eradicating an invasive plant ecosystem engineering and subsequent impacts of active replanting and passive revegetation on native plants and benthic invertebrate communities in San Francisco Bay, CA, USA. Much of this area was invaded by non-native hybrid cordgrass (Spartina alterniflora x S. foliosa). The hybrid was largely eradicated, and some locations have been actively replanted using native S. foliosa. We used this large scale experiment to sample plants and invertebrates in three site types: 1) eradicated not replanted (eradicated), 2) eradicated with replanting (replanted), and 3) native never invaded (native) (N=3/site type). We assessed plant community characteristics and sediment environmental parameters, as well as invertebrate community metrics. We hypothesized active replanting, as opposed to eradication without replanting, would speed return of invertebrate communities to a pre-invasion state, mediated by environmental changes correlated with quicker return of plants.
Results/Conclusions
After 1.5 years, percent plant cover in eradicated sites differed from native and replanted sites, which had equivalent plant cover (p=0.001). Conditions at the sediment surface in replanted areas quickly resembled those in native marshes, while eradicated sites remained distinct (sediment surface temperature p=0.001; percent plant canopy light penetration, p=0.001). Alternatively, belowground biomass did not quickly recovery, with replanted sites not differing significantly from eradicated sites. Epifaunal invertebrate abundance was similar between eradicated and replanted sites and not comparable to native sites, which had significantly higher average abundance (p=0.001). Infauna invertebrates exhibit a similar pattern, but are even slower to respond to revegetation than surface-dwelling epifauna. We conclude revegetation decreases the time necessary to return aboveground habitat to the pre-invasion state. This influences invertebrate communities, but this effect is slower for less mobile epifaunal invertebrates and infaunal invertebrates. These results may help explain why habitat restoration does not always attract the target bird and mammal species, since recovery of invertebrate prey may lag behind plant recovery.