Ecology of Native vs. Introduced Phragmites australis (Common Reed) in Chicago-Area Wetlands

Abstract

Rapid spread of Phragmites australis (common reed) in North American wetlands is widely attributed to cryptic invasion by an introduced lineage. However, in the Midwestern U.S., the native subspecies (subsp. americanus) may also exhibit rapid expansion. Where both lineages occur, wetland managers are sometimes unsure whether they should limit management activities to the introduced lineage or control both. We conducted field studies to contrast the ecology of native and introduced Phragmites by pairing patches of each with native reference vegetation. We measured each lineage’s association with environmental conditions, their growth metrics (stem heights, stem densities, and plant cover), and their invasiveness as indicated by the diversity and composition of associated plant communities. Introduced Phragmites exhibited more robust growth than the native, and its growth was more positively correlated with increases in soil nutrient availability and salinity. Areas with introduced Phragmites had lower plant diversity and altered species composition relative to reference vegetation. We did not observe similar evidence of invasiveness in native Phragmites. We encourage wetland managers to differentiate populations by lineage and, unless there is compelling evidence to do otherwise, restrict control efforts to the introduced lineage.