other Studies. — This type has not previously been reported in 

 Montana but has been reported in Wyoming (Bourgeron and 

 Engelking 1991) . 



16. Picea enqelmannii/Equisetvun arvense Type 



(PICENG/EQUARV; Engelmann spruce/field horsetail; G4 S3) 



Vegetation. — Picea engelmannii dominates the overstory and 

 Equisetum arvense is abundant in the undergrowth. The under- 

 growth is typically rich in species and high in total cover. 

 Species that are typically well represented include Linnaea 

 borealis . Actaea rubra , Fragaria virginiana , Smilacina 

 stellata . Thalictrum occidentale . and Calamaqrostis canaden- 

 sis . 



Physical Setting. — This type occurs on wet, flat sites in 

 alluvial basins. Elevations are around 6500 feet. The total 

 cover of litter, wood, and moss equals or exceeds 70% of the 

 ground surface. The soil surface is generally stable with no 

 evidence of accelerated erosion. 



Soils are derived from mixed alluvial parent materials 

 and are non-calcareous. These soils are wet throughout the 

 year and are often richly organic, e.g., Histic Cryaquolls. 

 Additionally, the soils are very deep, lack coarse fragments, 

 are loamy in texture, and have a very high available water 

 holding capacity. 



Adjacent Communities. — A complex of riparian forest, shrub, 

 and graminoid communities usually occur adjacent to the Picea 

 engelmannii /Equisetum arvense type. 



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

 Pfister et al. (1977) . 



17 . Populus trichocarpa/Cornus stolonifera Type 



(POPTRI/CORSTO; black cottonwood/red-osier dogwood; G4 S4) 



Vegetation. — Populus trichocarpa dominates the overstory and 

 Juniperus scopulorum is common in the middle layer. The 

 undergrowth is typically rich in species and high in total 

 cover. The pattern of occurrence of undergrowth species is 

 often highly variable spatially reflecting the pattern of 

 fluvial disturbances active on most Populus trichocarpa/Cornus 

 stolonifera sites. Species that are typically well repre- 

 sented include Cornus stolonifera . Rosa acicularis , Svmphori- 

 carpos albus, Galium boreale, Smilacina stellata . Poa palus- 

 tris . and Poa pratensis . 



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