PARENT SESSION
Poster Session #4: Invasions.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Spread and invasion of Lythrum salicaria (purple loosestrife): relative effects of seed supply and environmental factors.

HAGER, HEATHER¹, YAKIMOWSKI, SARAH², ECKERT, CHRIS², ^{1 2}

ABSTRACT- Lythrum salicaria (purple loosestrife) is an invasive plant thought to take over wetlands. However, large patches of uninvaded Typha spp. (cattails) exist within invaded wetlands and apparently uninvaded wetlands exist in close vicinity to wetlands containing Lythrum. We hypothesized that the mechanisms behind the observed pattern of Lythrum presence are primarily seed dispersal and secondarily, environmental factors affecting germination and survival. We germinated sediment samples from 11 uninvaded wetlands dominated by Typha, and from 10 Lythrum and 10 Typha stands within invaded wetlands. Seed bank composition was compared among the three stand types using nested analysis of variance. Lythrum was found in both types of invaded stands but not in uninvaded wetlands. In invaded wetlands, significantly more Lythrum seedlings germinated from Lythrum stands than Typha stands (p < 0.001). Therefore, initial spread of Lythrum depends on seed dispersal; local colonization depends also on factors allowing seed germination and survival. Although species richness did not differ significantly among stand types, fewer seedlings of native species were found in invaded stands than in uninvaded wetlands (p < 0.001). Whether Lythrum invasion causes this reduction in native seedlings is not yet clear, but it does suggest a feedback whereby fewer individuals of native species will produce less total seed, possibly leading to reduced species richness in invaded wetlands.

KEY WORDS: Lythrum salicaria, invasion of nonindigenous species, seed bank, wetlands