Encroachment of Gulf Coast Phragmites australis on the Lower Verde River
James Holderer1, Kara Clauser2
1Natural History Institute, Prescott, AZ, U.S.A.; jcholderer@comcast.net
2Center for Biological Diversity, Tucson, AZ, U.S.A.; kclauser@biologicaldiversity.org
Public land stakeholders and academics have reported a dramatic increase in Phragmites australis cover along Arizona’s Lower Verde River over the last century, however, quantitative field studies are limited and subspecies determinations have been lacking entirely. The three most common North American P. australis subspecies all occur in Arizona: P. australis subsp. americanus (Native), P. australis subsp. australis (Introduced), and P. australis subsp. berlandieri (Gulf Coast subspecies; nativity unknown). Genetic analyses of 36/36 leaf tissue samples from field surveys and herbarium specimens along the Lower Verde River, and neighboring East Verde and Salt rivers, have all been confirmed as Gulf Coast P. australis. This information greatly expands the academic community’s understanding of Gulf Coast P. australis distribution in the United States and places this lineage in the Lower Verde watershed as early as 1962. Our field surveys along the 40-mile Lower Verde Wild & Scenic River corridor recorded a >509% increase in cover since 2004. Our findings corroborate other studies’ concern that Gulf Coast P. australis is behaving invasively in the Southwest, as its distribution and cover rapidly expand along the Lower Verde River. Although Gulf Coast P. australis’ is relatively understudied, its similarities to the well-studied and problematic Introduced P. australis (namely in its tendency to grow monocultures) should be cause for concern and prompt further action on this subspecies.