Euonymus fortunei: Back-seat driver of environmental change?

Background/Question/Methods

Although some invasive species are well known to be the cause of native species declines, there is also evidence the some species may act as “passengers”, responding opportunistically to environmental changes which suppress native species.  It is also possible that environmental change and invasion interact to cause changes in native plant communities.  We tested these possibilities with Euonymus fortunei, an invasive species of the eastern deciduous forest. We experimentally removed Euonymus with hand pulling, herbicide and mulching and maintained invaded and un-invaded controls.  We also introduced seeds and seedlings of native species to the experimental plots to determine if dispersal limitation or Euonymus invasion constrained the restoration of the native plant community.

Results/Conclusions

Hand-pulling and herbicide reduced Euonymus cover by 88% and 98% respectively.  However, hand-pulling required more time, which may limit its effectiveness for managing Euonymus at large scales.  Native plant seedlings established well in all treatments, indicating that Euonymus fortunei may be unable to cause declines of established plants.  Ongoing monitoring will determine if these transplanted seedlings resist re-invasion in removal plots or exclude established Euonymus within control plots.  Natural recruitment of native species to removal areas was limited to ruderal species, suggesting that establishment of many native species within removal areas may be recruitment limited.  Further, very few native plants established from seed in Euonymus-invaded plots, demonstrating that Euonymus may be the driver of changes within plant communities by suppressing recruitment of native species.  We suggest that Euonymus fortunei may be acting as a “back-seat driver”, invading areas where competition from established native species is limited, but causing further changes to these communities by preventing recruitment of native plant species from seed.