Interaction of restored hydrological connectivity and herbicide suppresses dominance of a floodplain invasive species
Research Summary by Abby Bezrutczyk
Summary
While perennial pepperweed (Lepidium latifolium) is a widespread invasive in the western U.S., it’s an emerging invader in the northeast and a rapid-response target in NY. Control of this riparian weed can fall in two camps: conventional herbicide control, or ecological process restoration, but seldom are both approaches used. Hutchinson and colleagues tested the control of pepperweed in CA with herbicides and restored flooding, in order to see how the individual and paired treatments affect pepperweed abundance and native diversity. At two grassland sites and two floodplain sites where levees had been removed five years earlier, they measured the hydrologic regime, pepperweed stem count and cover, and alpha and beta vegetation diversity over nearly 10 years. They found that the long-duration (~125 day) floods were followed by reduced pepperweed populations, and that floodplain sites had greater native diversity than the grasslands. The treatments can also work in concert: the years following long-duration flood events and herbicide application had reduced pepperweed stem counts and increased floodplain native diversity.
Take-home points
- The lack of a natural disturbance regime (ie, perennial flooding) can be a driver for invasive colonization and establishment.
- “Restoring ecological function has the potential to reduce the impacts of invasive species, including long-term management costs and loss of species diversity.” (Hutchinson et. al 2020)
Management Implications
- “…Restored flood inundation onto a floodplain has the potential to reduce the dominance of [perennial pepperweed] over both short and long timescales.”
- “In areas where ecological function is not fully restored, the combination of applied control measures and the restored process (i.e. inundation, fire) can be successful in suppressing invasive weed populations.”
