(Phalaris arundinacea L.), and Native Plants in Wisconsin Wet Meadows

1 Corresponding author: [email protected]; (608) 238-4673; fax: (608) 262-7509 ABSTRACT: Twelve wet meadows in Dane County, Wisconsin showed vegetation patterns that correlate with hydrologic disturbance and presence of a clonal invasive grass, Phalaris arundinacea L., at two scales, 4500-m2 (0.45 ha) “sites” and 1-m2 plots. Sites with indicators of hydrologic disturbance had lower species richness and diversity than reference sites, and species richness, diversity, and mean coefficients of conservatism (Mean C) were inversely related to the abundance of Phalaris on sites. Within 1-m2 plots, 5.5 ± 0.4 (SE) species coexisted with Phalaris, while about twice as many coexisted with two widespread native graminoids: 11.5 ± 0.3 with Carex stricta Lam. and 10.6 ± 0.3 with Calamagrostis canadensis (Michx.) Beauv. Cover of Phalaris was approximately six times higher in plots on sites with disturbance indicators than on reference sites. Overall, plots with either Phalaris or hydrologic disturbance had 2/3 the species of plots lacking Phalaris on reference sites, as well as lower diversity and Mean C. These results suggest a strong negative effect of hydrologic disturbance or presence of Phalaris on the quantity and quality of species in a wetland. When Phalaris and disturbance indicators co-occurred, the difference was more severe. Plots with Phalaris on disturbed sites had 1/3 the species of reference plots and the lowest diversity and Mean C. Species were grouped into seven “response types” based on apparent sensitivity to the presence of Phalaris and hydrologic disturbance. Only the clonal grass Phragmites australis (Cav.) Trin. ex Steud. responded positively to the combination of Phalaris and hydrologic disturbance.