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

Ecosystem effects of Lythrum salicaria (Purple loosestrife) invasion in a restored freshwater wetland.

Welsch, Maryann¹, Yavitt, J.¹, ¹

ABSTRACT- Purple loosestrife (Lythrum salicaria) has invaded wetlands across North America and is known to have negative effects on native plant species and diversity; however, the effects of invasion on ecosystem processes are less well known. We examined how purple loosestrife influences ecosystem processes in stands of broad-leaved cattail (Typha latifolia), a native plant that competes with purple loosestrife. Processes were examined in plots with equal amounts of purple loosestrife and cattail and in experimental plots in which we removed purple loosestrife only or all vegetation from the area. As purple loosestrife and cattail differ physiologically, we expected to see significant differences in their decomposition characteristics. However, standing-dead cattail shoots and purple loosestrife stems had similar mass loss (20-25% of original mass) after one year. Purple loosestrife gained slightly more N than cattail during decay (220% and 175% of original N, respectively), and changes in Klason lignin over one year were the same for both species. Plant available N and soil respiration rates were not affected significantly by the presence of purple loosestrife and small differences in substrate-induced respiration rates existed between purple loosestrife and cattail root in-growth cores. While the presence of cattail as a native plant species may be more favorable in wetlands, overall differences between the influence of cattail and purple loosestrife on ecosystem-level processes measured in this study were subtle at best.

KEY WORDS: Purple loosestrife, Cattail