Physical Setting. — This type occurs on gravelly alluvial 

 parent materials on flat flood plains and terraces in wide 

 valley bottoms. Elevations are between 5000 and 5500 feet. 

 Litter plus wood cover equals or exceeds 60% of the ground 

 surface. The soil surface is generally stable with no evi- 

 dence of accelerated erosion. 



Soils are often Typic Udifluvents, are very deep with 

 textures varying from sandy to loamy, and are non-calcareous. 

 Available water holding capacity varies from low (sandy soils 

 high in coarse fragment content) to very high (loamy soils 

 without coarse fragments) . 



Adjacent Communities. --The Phalaris arundinacea , Eleocharis 

 spp. , and Salix exigua types occur on wetter sites. More 

 xeric sites often feature the Artemisia tridentata/Aqropyron 

 spicatum type. The Populus trichocarpa/ Cornus stolonifera 

 type intergrades with the Juniperus scopulorum or the Pseudot- 

 suqa menziesii/Cornus stolonifera types under conditions of 

 less fluvial disturbance (Hansen et al. 1991). 



Other Studies. --This type has been described in Montana by 

 Hansen et al. (1991) . 



18. Salix exigua Type 



(SALEXI; sandbar willow; G5 S4) 



Vegetation. — Salix exigua dominates the overstory (often with 

 a total canopy cover of 100%) . The undergrowth is typically 

 very depauperate due to the intense competition with S_^ exigua 

 and seldom exceeds 5% total cover. Species that are often 

 present in this sparse undergrowth include Cirsium arvense , 

 Mentha arvensis . and Phalaris arundinacea . 



Physical Setting. — This type occurs on gravelly alluvial 

 parent materials on flat flood plains and terraces in wide 

 valley bottoms. Elevations are between 5000 and 5500 feet. 

 Litter plus wood cover equals or exceeds 60% of the ground 

 surface and soil cover is typically around 20%. The soil 

 surface is unstable because of a lack of adequate vegetation 

 cover and the active fluvial disturbance regime present on S . 

 exigua sites. 



Soils are often Aquic Udifluvents, are very deep with 

 sandy textures, have a low available water holding capacity, 

 and are non-calcareous. Coarse fragment contents vary from 

 gravelly to very cobbly. 



Adjacent Communities. — Adjacent wetter sites are often open 

 water. Adjacent drier riparian communities often feature the 

 Populus trichocarpa/Cornus stolonifera type. 



28 



