Causes and Consequences of Invasive Plants in Wetlands: Opportunities, Opportunists, and Outcomes

Abstract

Wetlands seem to be especially vulnerable to invasions. Even though ≤6% of the earth's land mass is wetland, 24% (8 of 33) of the world's most invasive plants are wetland species. Furthermore, many wetland invaders form monotypes, which alter habitat structure, lower biodiversity (both number and “quality” of species), change nutrient cycling and productivity (often increasing it), and modify food webs. Wetlands are landscape sinks, which accumulate debris, sediments, water, and nutrients, all of which facilitate invasions by creating canopy gaps or accelerating the growth of opportunistic plant species. These and other disturbances to wetlands, such as propagule influx, salt influx, and hydroperiod alteration, create opportunities that are well matched by wetland opportunists. No single hypothesis or plant attribute explains all wetland invasions, but the propensity for wetlands to become dominated by invasive monotypes is arguably an effect of the cumulative impacts associated with landscape sinks, including import of hydrophytes that exhibit efficient growth (high plant volume per unit biomass).

Keywords:

• dominance
• exotic species
• landscape sink
• monotype
• Phalaris
• Typha x glauca

ACKNOWLEDGMENTS

Support from the National Science Foundation (DEB 0212005 to Zedler, Callaway, and Madon) for work on topographic heterogeneity is gratefully acknowledged. Work on P. arundinacea and Typha x glauca was supported by the U.S. Environmental Protection Agency Science to Achieve Results (EPA-STAR) program—the former on grant R828010 from (R. Lathrop, K. Potter, and J. Zedler, coinvestigators) and the latter on the Great Lakes Environmental Indicators (GLEI) project, cooperative agreement EPA/R-82867501 (G. Niemi, principal investigator). Although the research described in this article has been funded wholly or in part by the USEPA, it has not been subjected to the Agency's required peer and policy review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.