curve, and is quite similar between the two reporting stations; even their "relatively dry periods" 

 exhibit great similarity. 



Vegetation 



Vegetation patterns in Carter County primarily reflect differences in soils, geology, and topographic 

 position. Vast rolling plains with fine-textured, shale-derived soils are characterized by steppe 

 vegetation (shrub- and grass-dominated) in expressions that are conditioned by slope position, past 

 fires, and grazing regimes. Eroded shale-ridge systems and slope outwash support communities 

 dominated by specialized, drought and/or salt tolerant shrubs or herbs. Bentonite and shale ridge 

 systems and adjacent river terraces near Alzada support Montana's only oak woodlands. Ponderosa 

 pine grows mainly on sandstone outcrops. 



Steppe is defined as a climatically controlled vegetation type where the prevailing soils are too dry 

 for trees, and perennial grasses are well represented. In Carter County, both grassland steppe and 

 shrub steppe, where abundant shrubs form a higher layer, are present. The prevalence of grasslands 

 and shrublands across Carter County is apparent at a glance on the vegetation cover type map of 

 Kuchler ( 1 964). The magnitude of growing season drought and timing of precipitation are 

 hypothesized to be the two strongest climatic factors structuring the composition of steppe 

 landscapes (Daubenmire 1978). Carter County lies in the middle of mixed-grass prairie (steppe) 

 which extends fi-om the Rocky Mountains to the Dakotas and where mid-sized grasses and grass-like 

 plants predominate over short-grass or tall-grass species. Farther east, with gradually increasing 

 amounts of precipitation, tall-grass prairie lines the eastern margin of the Great Plains and extends 

 into the Midwest. 



The statewide vegetation cover type information that has recently been compiled by the University 

 of Montana shows vegetation patterns that correspond with the distribution of BLM-administered 

 lands in the county. ELM lands are most concentrated in areas of xeric shrubland and areas mapped 

 as badlands, the latter represenfing extremely sparse grasslands and shrublands. Grasslands on clay 

 soils are usually dominated by rhizomatous wheatgrasses (genera including Elymus and 

 Pascopyrum) while those on sandy soils generally have a higher component of needle- and-thread 

 {Stipa comata). Communities dominated by the warm season grass little bluestem {Schizachyrium 

 scopahum) are most common on sandy substrates, but may also occur on alluvial substrates eroded 

 from shales. Shrub communities on alluvial terraces that have fine textured soils are usually 

 dominated by black greasewood {Sarcobatus vermiculatus) or Wyoming big sagebrush {Artemisia 

 tridentata ssp. wyomingensis), while similar positions with sandy soils support silver sagebrush 

 {Artemisia cana). 



Previous vegetation studies in Carter County have been conducted by the U.S. Forest Service on 

 upland escarpments, representing less than 5% of the county area. Studies in adjoining counties have 

 been of limited extent or applicability for cataloguing or characterizing features across the Carter 

 County landscape. This study is a huge stride in creating a systematic vegetation resource inventory, 

 cataloguing and describing major types on BLM-administered lands, along with the field data and 

 information layers for understanding their place on the landscape. 



