Delicate wetland ecosystems that offer important wildlife habitats are threatened from multiple sources. One is the rapid expansion of non-native, invasive plants that choke out natural species and alter the wetlands.
Perennial pepperweed poses such a threat to seasonal wetlands in California and other Western states.
A study in the current issue of the journal Invasive Plant Science and Management examines characteristics of encroaching pepperweed. Two sites in the San Francisco Bay Area bioregion were studied to develop more effective management techniques against this weed.
Perennial pepperweed is native to temperate areas of Europe, Asia, and the Mediterranean. It accidentally came to the United States in the 1930s as a contaminant of sugarbeet seed.
In North America, the pepperweed has favored higher-elevation rangelands, riparian habitats, coastal marshlands, and seasonal wetlands.
Pepperweed releases billions of seeds per hectare each year, but few seedlings are encountered in most undisturbed wetland environments. As such, it is the plant’s roots, which run meters deep, with 60 percent of the plant below ground, that helps this invader gain territory.
The deep roots give pepperweed an advantage in dry periods, and increased water availability is beneficial to the expansion of the plant.
The most effective approach to controlling pepperweed should minimize disturbance of the desirable plant cover while controlling the expanding satellite infestations.
In the larger populations, pepperweed has the greatest stem density at the center of a patch, so attacking the edges can prove more beneficial and economic to stopping the spread.
When a site was disked, pepperweed spread was three times greater, indicating that disking should be avoided.
For federal and state resource managers seeking to control this invasive species and re-establish native vegetation, controlling new satellite populations while also working from the outer perimeters of pepperweed patches is most cost-effective.
This technique can slow the spread of pepperweed without leaving plant litter and seedbanks that can suppress the recovery of more desirable species.
Full text of the article, “Spread Dynamics of Perennial Pepperweed (Lepidium latifolium) in Two Seasonal Wetland Areas,” Invasive Plant Science and Management, Vol. 5, No. 1, January-March 2012, is available at http://www.wssajournals.org/.