The effects of various environmental factors on the success of tristylous Lythrum salicaria.

Abstract

Invasive species can influence a community, causing a decline or even extinction of native species. Lythrum salicaria, or purple loosestrife, is an exotic, tristylous plant that spreads over disturbed wetland areas in eastern North America. Rapid proliferation of this invasive demands a thorough understanding of the conditions in which it thrives most efficiently. In this study, I examined which environmental factors cause purple loosestrife to reproduce asexually versus sexually, and which soil conditions, sandy vs. organic, and dry vs. saturated, it prefers. I also explored factors that affect herbivory. My results showed that the three morphs were distributed in the expected, 1:1:1, ratio in high invasion levels, but not in low invasion levels. Purple loosestrife was more than three times as desnse in saturated, organic soil as it was in a dry or damp, mixed soil type. There was a greater average number of inflorescences per stem in highly invaded sites, and this average increased with an increase in plant height. As the number of adults increased, the number of seedlings also increased. Nearest neighbor values indicated greater proportion of same-morph pairs than expected. At high invasion levels, the porportion of herbivory was almost triple the proportion found in low invasion sites. Also, there was a strong correlation of increasing average plant height as well as increasing soil moisture with the proportion of herbivory. Overall, successful propagation of purple loosestrife seemed greatest in saturated, organic soils and in high density populations.