The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008 - 9:20 AM
Is Federally Threatened Water Howellia (Howellia aquatilis Gray) an Indicator of an Unfavorable Environment for Reed Canarygrass (Phalaris arundinacea L.)?
Laura A. Robison, Dept. of Environmental Sciences, Washington State University, Box 646410, Pullman, WA 99164-6410 and Linda H. Hardesty, Dept. of Natural Resource Sciences, Washington State University, Box 646410, Pullman, WA 99164-6410.
Reed canarygrass (Phalaris arundinacea L.) is an invasive perennial grass in temperate North American wetlands. It competes with tall, dense growth that shades competitors, tolerance of eutrophication, and broad ecological amplitude. No effective control exists.
Reed canarygrass dominates wetlands in Turnbull National Wildlife Refuge, Washington. Here, reed canarygrass occurs in wetlands that also support federally threatened Howellia aquatilis Gray. Reed canarygrass adversely impacts water howellia populations.
We hypothesized that howellia persists in some wetlands because habitat conditions there are less favorable to reed canarygrass. We located seven wetlands with howellia and six without that had been previously prioritized for reed canarygrass control. We mapped vegetation association and production changes along hydrological gradients, recording soils, aspect, tree and shrub canopy, coarse woody debris, reed canarygrass seed head and biomass production, and native biomass production. Howellia wetlands had significantly shorter upland-to-wetland gradients and smaller average size. In both wetland types, mid-gradient vegetation zones had the highest reed canarygrass production than zones near the ends of the gradient. Reed canarygrass biomass/m2 did not differ (P > 0.3400) between wetland types, and seed head production differed (P = 0.0339) in only one zone. Howellia wetlands had a greater (P = 0.0226) proportion of zones where reed canarygrass production was impaired, mostly by coarse woody debris or shrub canopy. Native biomass production was higher (P = 0.0737) in impaired zones in howellia wetlands. Wetlands with howellia also had more (P ≤ 0.0264) coarse organic soil on the wetland end of the gradient. Together, our results did not support the hypothesis, though there were some differences between wetland types. The persistence of howellia in some wetlands may be due to more shade-generating canopies and coarse woody debris, less historical agriculture in the smaller basins where it is found, or differing ground water regimes.
Reed canarygrass dominates wetlands in Turnbull National Wildlife Refuge, Washington. Here, reed canarygrass occurs in wetlands that also support federally threatened Howellia aquatilis Gray. Reed canarygrass adversely impacts water howellia populations.
We hypothesized that howellia persists in some wetlands because habitat conditions there are less favorable to reed canarygrass. We located seven wetlands with howellia and six without that had been previously prioritized for reed canarygrass control. We mapped vegetation association and production changes along hydrological gradients, recording soils, aspect, tree and shrub canopy, coarse woody debris, reed canarygrass seed head and biomass production, and native biomass production. Howellia wetlands had significantly shorter upland-to-wetland gradients and smaller average size. In both wetland types, mid-gradient vegetation zones had the highest reed canarygrass production than zones near the ends of the gradient. Reed canarygrass biomass/m2 did not differ (P > 0.3400) between wetland types, and seed head production differed (P = 0.0339) in only one zone. Howellia wetlands had a greater (P = 0.0226) proportion of zones where reed canarygrass production was impaired, mostly by coarse woody debris or shrub canopy. Native biomass production was higher (P = 0.0737) in impaired zones in howellia wetlands. Wetlands with howellia also had more (P ≤ 0.0264) coarse organic soil on the wetland end of the gradient. Together, our results did not support the hypothesis, though there were some differences between wetland types. The persistence of howellia in some wetlands may be due to more shade-generating canopies and coarse woody debris, less historical agriculture in the smaller basins where it is found, or differing ground water regimes.