Document: DAN-3-38-25

Resource competition between the exotic invasive, purple loosestrife, and native broad-leaved cattail: Evidence from field observations.

BUNKER, D.E.* and W.P.CARSON

University of Pittsburgh, Pittsburgh, PA 15260 USA ¹

Abstract:
We hypothesize that purple loosestrife (Lythrum salicaria), an exotic wetland macrophyte, invades and displaces broad-leaved cattail (Typha latifolia) through resource competition. Under this hypothesis, light availability, soil resource availability, or both should be lower in loosestrife stands than in stands of cattail. As part of a larger study to test this hypothesis, we measured light and soil resource availability in stands of natural vegetation in six northwestern Pennsylvania freshwater marshes. We established 48 1m² plots in stands of both species. We measured light attenuation monthly with a Li-Corr line quantum sensor at 50 cm intervals from the soil surface to the canopy. To measure soil resource availability, we collected porewater samples at depths of 0, 5, 10, and 15 cm, and then analyzed these samples for ammonium and nitrate concentration. Our results demonstrate a dramatic difference in light attenuation between loosestrife and cattail. At mid-story heights of 100 and 150 cm, loosestrife intercepted 86% and 60%, respectively, of ambient light, compared to only 51% and 28% for cattail (p<0.001). We found no significant differences in soil resource availability between the two species. These results strongly suggest that competition between loosestrife and cattail is mediated through indirect competition for light, and that loosestrife is able to invade and displace cattail by reducing light availability. We are currently testing this hypothesis with extensive common garden and field experiments. By directly comparing the resource competitive ability of native and exotic species, ecologists may be able to make clear predictions regarding the invasive potential of exotic species.

Keywords: Resource competition, plant competition, invasive species, Lythrum, Typha

This abstract is being presented at: 10:30 AM in session:
RESTORATION ECOLOGY AND INVASIONS