landcover descriptions for the southwest regional gap analysis project

not always significantly contribute to the canopy, they can be very important. Some dominant forb species includeAmbrosia psilostachya, Echinacea angustifolia, and Lygodesmia juncea. Oak species such as Quercus macrocarpacan occur also in areas protected from fire due to topographic position. This can cause an almost oak savannasituation in certain areas, although fire suppression may allow for a more closed canopy and expansion of bur oakbeyond those sheltered areas. In those situations, further information will be needed to determine if those largerareas with a more closed canopy of bur oak should be considered part of Western Great Plains Dry Bur Oak Forestand Woodland (CES303.667). Likewise, within the mixedgrass system, small seeps may occur, especially duringthe wettest years. Although these are not considered a separate system, the suppression of fire within the region hasenabled the invasion of both exotics and some shrub species such as Juniperus virginiana and also allowed for theestablishment of Pinus ponderosa in some northern areas.DISTRIBUTIONRange: This system is found throughout the central and southern areas of the Western Great Plains ranging fromsouthern South Dakota into northern Texas.Ecological Divisions: 303TNC Ecoregions: 27:P, 28:P, 29:C, 32:C, 33:C, 37:PSubnations/Nations: CO:c, KS:c, NE:c, OK:c, SD:c, TX:cCONCEPTAlliances and Associations:• (COMPLEX)Blacktailed Prairie Dog Town Grassland Complex (CECX005703)• ARTEMISIA TRIDENTATA SSP. WYOMINGENSIS SHRUB HERBACEOUS ALLIANCE (A.1527)Artemisia tridentata ssp. wyomingensis / Mixed Grasses Shrub Herbaceous Vegetation (CEGL001534)• CORNUS DRUMMONDII SHRUBLAND ALLIANCE (A.3558)Cornus drummondii - (Rhus glabra, Prunus spp.) Shrubland (CEGL005219)• CYNODON DACTYLON HERBACEOUS ALLIANCE (A.1279)Cynodon dactylon Herbaceous Vegetation (CEGL004701)• HESPEROSTIPA COMATA - BOUTELOUA GRACILIS HERBACEOUS ALLIANCE (A.1234)Hesperostipa comata - Bouteloua gracilis - Carex filifolia Herbaceous Vegetation (CEGL002037)Hesperostipa comata - Carex filifolia Herbaceous Vegetation (CEGL001700)Hesperostipa comata - Carex inops ssp. heliophila Herbaceous Vegetation (CEGL001701)Hesperostipa comata Colorado Front Range Herbaceous Vegetation (CEGL001702)• HESPEROSTIPA CURTISETA - ELYMUS LANCEOLATUS HERBACEOUS ALLIANCE (A.3523)Hesperostipa curtiseta - Elymus lanceolatus Herbaceous Vegetation (CEGL002253)• JUNIPERUS VIRGINIANA FOREST ALLIANCE (A.137)Juniperus virginiana var. virginiana / Schizachyrium scoparium Forest (CEGL003628)• KRASCHENINNIKOVIA LANATA DWARF-SHRUB HERBACEOUS ALLIANCE (A.1565)Krascheninnikovia lanata / Bouteloua gracilis Dwarf-shrub Herbaceous Vegetation (CEGL001321)• PASCOPYRUM SMITHII HERBACEOUS ALLIANCE (A.1232)Pascopyrum smithii - Bouteloua gracilis Herbaceous Vegetation (CEGL001578)Pascopyrum smithii - Hesperostipa comata Central Mixedgrass Herbaceous Vegetation (CEGL002034)Pascopyrum smithii Herbaceous Vegetation (CEGL001577)• PLEURAPHIS MUTICA HERBACEOUS ALLIANCE (A.1249)Pleuraphis mutica - Buchloe dactyloides Herbaceous Vegetation (CEGL002272)• POA PALUSTRIS SEMI-NATURAL SEASONALLY FLOODED HERBACEOUS ALLIANCE (A.1409)Poa palustris Herbaceous Vegetation (CEGL001659)• POA PRATENSIS SEMI-NATURAL HERBACEOUS ALLIANCE (A.3562)Poa pratensis - (Pascopyrum smithii) Semi-natural Herbaceous Vegetation (CEGL005265)• QUERCUS MACROCARPA WOODED MEDIUM-TALL HERBACEOUS ALLIANCE (A.1505)Quercus macrocarpa / Mixedgrass Loam Wooded Herbaceous Vegetation (CEGL002163)Quercus macrocarpa / Mixedgrass Sand Wooded Herbaceous Vegetation (CEGL002162)Quercus macrocarpa / Mixedgrass Shale Wooded Herbaceous Vegetation (CEGL002164)• SARCOBATUS VERMICULATUS INTERMITTENTLY FLOODED SPARSELY VEGETATED ALLIANCE (A.1877)Sarcobatus vermiculatus / Sporobolus airoides Sparse Vegetation (CEGL001368)• SCHIZACHYRIUM SCOPARIUM - BOUTELOUA CURTIPENDULA HERBACEOUS ALLIANCE (A.1225)Juniperus virginiana var. virginiana / Schizachyrium scoparium - Bouteloua curtipendula Great Plains HerbaceousVegetation (CEGL004066)Schizachyrium scoparium - Bouteloua (curtipendula, gracilis) - Carex filifolia Herbaceous Vegetation (CEGL001681)Schizachyrium scoparium - Bouteloua curtipendula - Bouteloua gracilis Central Plains Herbaceous Vegetation(CEGL002246)Ecological Systems: Copyright © 2003 NatureServe 121