PARENT SESSION
Oral Session #39: Invasions: Effects of invaders -- Aquatic, marsh, riparian. Presiding: C. Kolar.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Madison Ballroom C.
Impact of purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinaceae) density on plant and moth communities in northwest Oregon.
Schooler, Shon1, McEvoy, Peter 1, Coombs, Eric2, 1 2
ABSTRACT- Introduced plant species may affect local plant and animal community diversity and species richness. We studied the association between varying densities of two introduced wetland plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinaceae), on plant and moth species richness in 12 emergent palustrine wetlands in northwestern Oregon. Four wetlands were dominated by canary grass (all naturally occurring (NOW's)), four were dominated by loosestrife (two created (CW's), two NOW's), and four were reference wetlands without canary grass or loosestrife (three CW's, one NOW). We measured plant community composition as percent cover and sampled the moth community using blacklight traps. Ninety-eight plant and 86 moth species were identified. As canary grass density increased from 0 to 81%, plant species richness declined from 32 to 4. There was no clear negative association between loosestrife density and plant species richness, however loosestrife cover only varied between 0 and 29%. We found a positive correlation between moth and plant species richness in the seven NOW's. However, although plant species richness averaged 26 in the five CW's, the mean number of moth species was 20, which was fewer than expected. A strong negative association between reed canary grass abundance and plant and moth species diversity suggests that canary grass invasion reduces biodiversity, whereas the impact of loosestrife on biodiversity was inconclusive. We also detected a negative association between CW's and moth species richness.
KEY WORDS: purple loosestrife, reed canary grass, invasive species, community impacts