PARENT SESSION
Poster Session #6: Invasive Species Ecology: Insects and wetlands.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
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Absolute versus per-gram effects of purple loosestrife (Lythrum salicaria) on native wetland seedling growth and competition.
Hager, Heather*,1, 1 University of Regina, Regina, SK, Canada
ABSTRACT- Plants affect their environments by altering conditions such as light penetration, nutrient cycling and microtopography. I examined the hypothesis that mature plants of different species exert differential effects on the growth of seedlings. I predicted that 1) invasive species (Lythrum salicaria) facilitate growth of conspecific seedlings and inhibit growth of native species (Lythrum alatum, Typha angustifolia and Typha latifolia); 2) invasive species suppress growth of seedlings more than do mature plants of native species; and, 3) seedlings of invasive species are better competitors than native seedlings and are less suppressed by established vegetation. One individual of each of four seedling species was transplanted into eight blocks of five wetland mesocosm-types (one unvegetated control and four vegetated monocultures). Seedlings were harvested after seven weeks and relative growth rates and relative competition indices were compared using split-plot analysis of variance. Seedling growth rates were lowest in established Lythrum salicaria vegetation on both absolute and per-gram of mature vegetation bases. In terms of competition, seedlings of Lythrum alatum experienced the weakest, and Typha angustifolia the strongest, suppressive effects. Mature Lythrum salicaria was the most suppressive on an absolute basis, but was the least suppressive when biomass of the established vegetation was accounted for. These results are contrary to expectations and suggest that per-gram effects of exotic Lythrum salicaria on growth of heterospecifics are weaker than the effects of established vegetation of native species.
KEY WORDS: Lythrum salicaria (purple loosestrife), invasive species, relative competition intensity, target seedling transplants