Wetland vegetation before and after experimental purple loosestrife removal

Abstract

Abstract Purple loosestrife (Lythrum salicaria) is considered one of the worst invasive non-native species of North American wetlands, but its reputation rests on few published, quantitative field studies. This study described the vegetation of two sites (one flooded, one drier) within a heavily invaded wetland in southeastern New York, in order to investigate the common claim that purple loosestrife produces monospecific stands. Native species richness per square meter was 6.8, on average, with mean percent cover ranging from 0.03 to 6.7%, compared to 49% for purple loosestrife. One grass, Phalaris arundinacea, covered on average 31.1% of the area in drier site plots. Twenty-six native taxa were found in a total of 18 1-m2 plots. I also conducted an experimental manipulation of the plant community in both sites to demonstrate the role of purple loosestrife in gap colonization. Three 1-m2 experimental gaps in each site were recolonized by purple loosestrife at very low density after three years (mean perc...