Impacts of Lythrum salicaria invasion on plant community and soil properties in two wetlands in central New York, USA

While the spread of the exotic Lythrum salicaria L. across wetlands in North America is thought to negatively affect the performance and diversity of native species, the actual impacts of L. salicaria invasion on community dynamics and ecosystem properties are not well understood. To determine whether L. salicaria affects community aboveground biomass, native species biomass, or soil properties, we studied two common situations in central New York State where L. salicaria invaded (i) an abandoned agricultural field and (ii) a relatively pristine wetland with low species diversity. In the agricultural site, nearly monospecific stands of L. salicaria and Phalaris arundinacea L. had nearly identical shoot mass (approx. 850 g·m–2) but divergent soil characteristics. Inorganic nitrogen was significantly higher under L. salicaria than under P. arundinacea. The low-diversity site is dominated by Carex lacustris Willd., with distinct areas codominated by either L. salicaria or Typha latifolia L. In this site, we found that areas with a codominant species had significantly more total aboveground biomass than those dominated by C. lacustris, suggesting that L. salicaria invasion does not significantly lower native species biomass. However, most soil nutrient levels did not differ among vegetation zones, indicating that species composition changes did not alter soil properties in the short term. This study supports a growing literature suggesting that L. salicaria invasion may not negatively impact relatively pristine wetlands as previously believed.