Causes and consequences of purple loosestrife (Lythrum salicaria L.) invasions on native wetlands

Laurence Seth Fernberg, Fordham University


The objectives of this research were to investigate the effects of moisture and salinity on competition between an introduced and a native macrophyte and to examine decomposition as affected by plant part, salinity, and habitat. Flooding has little effect on cattail, but inhibits Lythrum by $>$50%. With interspecific competition, submersion reduces Lythrum growth, but Lythrum outcompetes Typha in emersed conditions. A two year Lythrum seedling invasion study conducted at 2 moisture treatments resulted in greater Lythrum seedling mortality, however the individual plants were 3$\times$ larger than year one plants. This suggests Lythrum is self-thinning with fewer and larger survivors. A decomposition experiment was conducted to compare mass loss from leaves and stems of these species over 330 days in microcosms. Leaves of Lythrum had the most rapid decay rate followed by Typha leaves and Typha and Lythrum stems evidence suggests that initial amounts of lignin are inversely related to decay rate. Lythrum leaves initially released significantly greater amounts of NH$\sb4\sp+$(4$\times$) and PO$\sb4\sp{3-}$ (250$\times$) than Typha leaves. Laboratory experiments included manipulating salinity on seed germination and seedling growth and effects of salinity on decomposition and nutrient cycling. Hudson River field results indicate habitat and site had no effect on Lythrum decomposition. Lythrum decomposition rate was slower than Typha suggesting that Lythrum will accumulate and alter nutrient fluxes in wetlands. Low salinities and population had no effect on decomposition. The saline Lythrum population was faster than the freshwater which may result from differences in resident microbes. Experiments indicate that both tolerate low salinities but survival is inhibited at high salinity. Lythrum was able to outcompete Typha at all salinities. Salinity had no effects on Typha. Interspecific planting had greater effect on Typha than intraspecific, the reverse was observed in Lythrum. This work will aid in determining causes and effects of invasive species on wetland communities and their effects on nutrient cycling, and may help develop effective management methods.

Subject Area


Recommended Citation

Fernberg, Laurence Seth, "Causes and consequences of purple loosestrife (Lythrum salicaria L.) invasions on native wetlands" (1998). ETD Collection for Fordham University. AAI9816343.