31 



usucilly have bottxxn surfaces of firm, consolidated clay and 

 organic sediments. They are virtually always particilly 

 surrounded by broadleaf deciduous trees, such as Populus 

 trichocarpa (Black OottcaTwood) and/or P. tremiloides ((;^Jaking 

 Aspen) in Mcxitana, and Fraxinus latifolia (Ash) or Ojercus 

 qarryana (Garry Oak) in Washington. Characteristic associated 

 aquatic species iiiclude Carex vesiceuria (Inflated Sedge) , Sium 

 suave (Hemlock Water-parsnip) , and/or Equisetum fluviatile (Water 

 Horsetail) in Montana. In Idaho, H. aquatilis occurs in a small 

 pcxid in a cutoff river channel, in a broad valley bottoro 

 surrounded by low, forested hills. Rangewide, the ponds are 

 generally filled by spring rains or sncwmelt run-off, and many 

 are usuzdly dry by the end of the growing season. Hcv>ellia 

 aquatilis occurs at elevations from 3 m (10 feet) in Washington 

 to 1350 m (4420 feet) in Montana. 



B. Riysical charactfiristics . 



1. diinate. 



a. Kcppen clinate classification (ext^mit sites) : Types 

 Csa and Csb (warm, maritiine or semimaritime types with 

 dry sunmers) , and Dfb (cool tenperate climate, with 

 numerous sunner thunderstonns) (Visher 1954). 



b. Rogicnal nacrocliinate: The climates in which {}. 

 dciuatilis has been found range from semi-eurid 

 Meditteranean (California; R. Bittman, pers. ocnin.) to 

 moist ten|3erate (northwestern Montana) . 



Near the distributional area of iJ. aquatilis in the 

 Swan Valley, Montana, the closest climatological 

 stations are located in Bigfork (3010 ft. (918 m) 

 elevation) ard Seeley lake (4100 ft. (1250 m) 

 elevation) . Data for the period 1951-1980 aire provided 

 by the U.S. Department of Oorineroe (1982). At Bigfork, 

 the mean annual precipitation was 56.08 an (22.08 

 in.); the mean annual tenperature was 7.5* C (45.5* F) , 

 and the mean July maximum temperature was 27.6* C 

 (81.7* F) . At Seeley Lake, the mean annual 

 precipitation was 56.16 cm (22.11 in.); the mean 

 annual tenperature was 5.2* C (41.3* F) , and the meein 

 July maximum tenperature was 27.8* C (82.0* F) . 



The climate of northern Idaho is influenced primaurily 

 by Pacific maritime air. However, Idaho is 500 to 650 

 km inland from the Pacific Ocean, and the Cascade 

 Mountains separate Idaho from the coast. TYie distance 

 and the mountain barrier result in a climate with many 

 ocMitinental chcU3cteristics. Because prevailing 

 westerly winds blew inland from the Pacific Ocean, 

 winters are warmer and milder than mi^t be expected. 

 These mild, moist winds result in winters that are 

 humid and cloudy. Snowfall is heavy in the mountains. 



