Thesis
A test of federally threatened water howellia (Howellia aquatilis Gray) presence as an indicator of unfavorable environmental conditions for invasive reed canarygrass (Phalaris arundinacea L.)
Washington State University
Master of Science (MS), Washington State University
2007
Handle:
https://hdl.handle.net/2376/100871
Abstract
Reed canarygrass (Phalaris arundinacea L.) is an invasive perennial grass in North American temperate wetlands. It is an effective competitor due to tall, dense growth that creates deep shade, high responsiveness to eutrophication, and broad ecological amplitude. Attempts to control the species have been unsuccessful. Reed canarygrass dominates wetland habitats in Turnbull National Wildlife Refuge, near Cheney, Washington. At Turnbull, reed canarygrass occurs in wetlands that also support the federally-listed threatened plant Howellia aquatilis Gray. Studies show that reed canarygrass adversely impacts water howellia populations. We hypothesized that water howellia persists in certain wetlands because habitat conditions are less favorable to reed canarygrass than in other wetlands. To test this hypothesis we located seven wetlands with water howellia and six without howellia that had dominant reed canarygrass stands. We mapped vegetation association and standing crop changes along a hydrological gradient, and recorded site characteristics including soils, aspect, tree and shrub canopy, and coarse woody debris. We also recorded reed canarygrass seed head density, native plant standing crop, and aboveground rooting behavior of reed canarygrass. Wetlands with water howellia had significantly shorter (P = 0.0423) upland-to-wetland gradients, consistent with their smaller average size. In both wetland types, mid-gradient vegetation zones were longer and had higher reed canarygrass biomass than zones nearer the ends of the gradient. Reed canarygrass biomass was not significantly different (P > 0.34) between wetland types in any zones, and seed head density was significantly different (P = 0.0339) in only one vegetation zone. Wetlands with water howellia had a significantly greater (P = 0.0226) proportion of zones where reed canarygrass production was impaired, most often by coarse woody debris or shrubs. Soil profiles of wetlands with howellia also had significantly (P < 0.03) more coarse organic soil on the wetland end of the gradient. Our results did not support the hypothesis, though there were some differences in reed canarygrass performance between wetland types. The persistence of water howellia in some wetlands may be due to more shade-generating canopies and coarse woody debris, or to different ecological or historical characteristics in the smaller basins where it occurs.
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Details
- Title
- A test of federally threatened water howellia (Howellia aquatilis Gray) presence as an indicator of unfavorable environmental conditions for invasive reed canarygrass (Phalaris arundinacea L.)
- Creators
- Laura Ann Robison
- Contributors
- Linda H. Hardesty (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525131101842
- Language
- English
- Resource Type
- Thesis