Population and Habitat Monitoring of Howellia Aquatils (Water Howellia) at the Harvard-Palouse River Flood Plain Site, Idaho: Sixth-Year (2004) Results

摘要

Water howellia (Howellia aquatilis) is an aquatic macrophyte that is listed as threatened by the U.S. Fish and Wildlife Service. The single known Idaho location of the species occurs on the flood plain of the Palouse River in northern Idaho, in three small ponds formed by fluvial processes. The ponds are the low points of abandoned channels or channel migration scars and dry each summer. Threats to the population include invasion by three non-native speciesreed canarygrass (Phalaris arundinacea), sweet flag (Acorus calamus), and climbing nightshade (Solanum dulcamara). Water howellia populations and pond water depths at the site have been monitored since 1999. Photopoints were established in 2000. This is the sixth annual report documenting monitoring results. In 2004, flowering took place in late June when the water was 23-36 cm deep. Although absent from pond 1 for the third consecutive year, water howellia occupied more area in pond 3 than in any previously monitored year, and was unusually dense in pond 2. In addition, several water howellia plants appeared in portions of pond 3 where reed canarygrass abatement efforts had taken place; plants had not been documented in those areas in earlier monitoring years. In 2003, we installed transects in ponds 2 and 3 for measuring cover and frequency of water howellia and associated plants, and for detecting the results of weed abatement efforts on reed canarygrass and sweet flag. In 2004, we established a monitoring transect in pond 1 and added a third transect in pond 2. We took photos from established photopoints on 28 June 2004. We continued weed suppression measures for reed canarygrass and sweet flag in ponds 2 and 3. For reed canarygrass these consisted of clipping, covering, and limited excavation; we pulled sweet flag shoots in pond 2. Monitoring information, along with results of weed suppression measures, will provide a basis for possible future management of the site.