Benton Lake National Wildlife Refuge 



MuLLAN Trail Research Natural Area 



ENVIRONMENT: 



The MuUan Trail RN A is a 392 acre segment of gently 

 rolling terrace and fan landforms associated with 

 Glacial Lake Great Falls. There are no surface drainage 

 features, and it lies within the closed-basin topography 

 surrounding Lake Benton. The limited relief in 

 elevation ranges from 3628 to 3650 ft. Soils have 

 developed from alluvium and lacustrine deposits, made 

 up of fine-textured clays of the Pendroy Series (two 

 map units represented) with slow to moderate rates of 

 runoff. The semi-arid continental climate has peak 

 precipitation in May followed by June (Climate data 

 from Great Falls, Western Regional Climate Center). 



VEGETATION: 



The vegetation is well-developed and relative uniform, 

 made up a single grassland plant association. The 

 overall visual impression is of homogeneity across the 

 "sea of grass." It is an island of intact natural 

 vegetation, a fragment of a formerly extensive type, 

 now surrounded by agricultural lands and tamegrass. 



Pascopyrum srrdtha — NaseUa iAridula Herbaceous 



Vegetation 



[PASSMI-NASVIR] 



western wheatgrass - green needlegrass grassland 



This is the one major plant association present in the 

 RNA. Its composition differs from place to place within 

 the RNA but the two plots established at the far ends 

 of the area evidence a high degree of similarity in 

 both composition and cover by the dominant species. 

 Western wheatgrass (Pascopyrum smithii) , green 

 needlegrass (Nasella viridula), prairie junegrass (Koeleria 

 macraruha) and narrow-leaved sedge (Carex stenophylla) 

 are the dominant graminoids with this component's 

 total canopy cover ranging around 70%. The forb 

 component is low in species, with three that are more 

 common than all others: poverty- weed (Iva axillaris), 

 plains bahia (Picraderuopsis oppositifolia) , and scarlet 

 globemallow (Sphaeralcea coccirxea). It is possible that 

 forb numbers and flowering levels are suppressed by 

 litter accumulation, but this association as found on 

 heavy soils is intrinsically limited in forb diversity. 

 Patterns of variation from place to place within the 



area may correspond with land use differences or small- 

 scale natural disturbance such as burrowing animals. 



The PASSMI - NASVIR plant association occurs in 

 Montana, North Dakota, South Dakota, Wyoming, 

 Saskatchewan, and southwestern Manitoba. It is 

 ranked G4 by TNC (Schneider et al. 1997). Nasella 

 viridula is both more palatable and more sensitive to 

 grazing than Pascopyrum smithii and also has a narrower 

 ecological amplitude. In the Yellow Water Triangle 

 area jorgensen (1979) notes the indicator value of 

 Nasella viridula for recognizing sites with a higher soil 

 moisture status, such as swales, toeslopes and moist 

 terraces dominated by silver sage (Artemisia carui). 



There is a need to refine U.S. and Canadian vegetation 

 classification as it involves this type. Based on a study 

 of relict and near pristine sites, Coupland (1961) 

 identifies a porcupine grass - thickspike wheatgrass 

 grassland (Sapa curtiseta - Agropyron dasystachyum 

 Herbaceous Vegetation) as the major grassland type on 

 dark brown and brown soil zones of southern Canada, 

 essentially the prevaling mesic sites in landscape. 

 Coupland notes that south of the 49'*' parallel the 

 importance value of porcupine grass (Sapa curtiseta; 

 includes some or all of what has been treated as Stipa 

 spartea in Montana) as determined by cover declines 

 drastically and that Agropyron dasystachyum (synonym: 

 Elymus lanceolatus) exhibits a gradual decrease as well. 

 Stipa curtiseta was noted as dominant elsewhere in the 

 RNA system at Tepee Hills. DeVelice et al. (1995) 

 documented the importance of a PASSMI - NASVIR 

 association across the northern tier of Montana 

 counties. They recognized Poscofryrum smithii and 

 Elymus lanceolatus as ecological equivalents for site 

 identification and noted the difficulty of field 

 discrimination of these two species based on vegetative 

 or reproductive characters. [Plots 

 NHMTECMT97SC0001, NHMTECMT97SC0002] 



OVERALL BIODIVERSITY SIGNIFICANCE: 

 The MuUan Trail RNA represents a good quality 

 occurrence of what may have been a common if not the 

 prevalent plant association of the Hi-Line (Glaciated 

 Plains Section) of Montana under presettlement 

 conditior«. It is a mesic, productive grassland type of 

 the Great Plains biome, and it is estimated that over 90 

 % of its original pre-settlement extent has been plowed. 



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