Montana Field Guide

Sand Prairies are a unique grassland type occurring mostly as localized patched in sandy soils across the western Great Plains. In Montana, they are most common in the very eastern part of the state though can be found in scattered locations across the plains. These habitats are largely confined to areas where sandstone caprocks have weathered, depositing large amounts of sand onto the adjacent landscape. Patch size often corresponds to the area of exposed caprock sandstone, and small patches predominate, but larger patches are found embedded in the encompassing Great Plains Mixed Grass Prairie, and usually occupy higher positions in local landscapes where former caprock formations have eroded into more subdued and planar topography. Soils can be relatively thin or deep due to varying amounts of downslope movement of weathered sands. Soil textures are mostly sands and sandy loams. Needle and thread (Stipa comata) is often the dominant grass species. Other common species include Prairie Sandreed (Calamovilfa longifolia), Sand Bluestem (Andropogon hallii), Bluebunch Wheatgrass (Elymus spicatus), Threadleaf Sedge (Carex filifolia) and Carex inops ssp. heliophila are common dominants. Big Bluestem and Sand Bluestem are found only as small patch occurrences in easternmost Montana, while other graminoids typical of the mixedgrass prairies are also found in Sand Prairie habitats. Soapweed Yucca (Yucca glauca) commonly occurs on these sandy, upland sites.

This Group is equivalent to the Great Plains Sand Prairie Ecological System.

Grass-dominated; Sandy Soils; Great Plains Region; Warm and Cool Season Grasses

Typical Dominants: Prairie Sandreed (Calamovilfa longifolia), Sand Bluestem (Andropogon hallii), Needle-and-Thread (Stipa comata), Carex inops ssp. heliophila

This Group is found in mostly localized areas throughout the Great Plains in Montana but is most common in the very eastern part of the state including in areas such as the Medicine Lake Sandhills and around Medicine Rocks State Park. Scattered occurrences may be found in central Montana near the western edge of the Great Plains in pockets of sandy soil.

In Montana, G889 occurs in Level III Ecoregions: 42 (Northwestern Glaciated Plains) and 43 (Northwestern Great Plains).

In Montana, G889 occurs or potentially occurs within these Major Land Resource Areas: 46 Northern and Central Rocky Mountain Foothills, 52 - Brown Glaciated Plains; 53A - Northern Dark Brown Glaciated Plains; 53B - Central Dark Brown Glaciated Plains; 54 - Rolling Soft Shale Plain, 58A,B,C,D - Northern Rolling High Plains, 60B - Pierre Shale Plains, Northern Part.

Small Patch and Large Patch

This group is found on sandy and sandy loam soils, generally in areas with a rolling topography, although it can occur on ridges, midslopes and/or lowland areas. Occurrences are often intermixed with the Great Plains Dry Mixed Grass Prairie, which occurs on less sandy soils. The climate is temperate, mostly continental and semi-arid to arid. Precipitation occurs mostly in the Spring. Summers are hot and dry, except for locally occurring, high-intensity convective storms. Soils are susceptible to wind erosion. Wind is a dominant factor that shapes the landscape where this group occurs as it sometimes scours sand and vegetation from small areas and creates blowouts. In most of eastern Montana, substrates supporting this system have weathered in place from sandstone caprock; thus the soils are relatively thin.

Graminoid species dominate the sand prairies, though shrubby species and forbs are often present. Prairie Sandreed (Calamovilfa longifolia), Sand Bluestem (Andropogon hallii), Needle-and-Thread (Stipa comata), Bluebunch Wheatgrass (Elymus spicatus), Threadleaf Sedge (Carex filifolia) and Carex inops ssp. heliophila are common dominants. Big Bluestem and Sand Bluestem are found only as small patch occurrences in easternmost Montana, while other graminoids typical of the mixedgrass prairies are also found in Sand Prairie habitats. Soapweed Yucca (Yucca glauca) commonly occurs on sandy, upland sites. Characteristic forbs include species of Scurf pea and Breadroot (Pediomelum, Psoralidium), Narrow-leaved Purple Coneflower (Echinacea angustifolia) and several species of Milkweed (Asclepias). Skunkbush Sumac (Rhus trilobata) and Creeping Juniper (Juniperus horizontalis) are commonly found on shallow sandy soils, often associated with breaklands. Other shrubs occasionally found within this type include Silver Sage (Artemisia cana) and Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis).

In Montana, Sand Prairie vegetation types are represented by 2 Alliances and 5 Associations within the National Vegetation Classification. These include 1 Alliance and 3 Associations that have a shrubby vegetation component. Additional, herbaceous-dominated types may exist in the state, either undescribed or unattributed to Montana.

Wind is a dominant factor that shapes the landscape where this group occurs. Wind sometimes scours sand and vegetation from small areas and creates blowouts. These blowouts may initially be colonized by species such as Yucca glauca, and Indian Ricegrass (Oryzopsis hymenoides). Eventually, these blowouts succeed to other communities (Savage 1937, Ramaley 1939b, Tolstead 1942, Harrison 1980). Fire frequency and extent are also thought to have declined since settlement because of fuel removal by livestock grazing and fire control (Burzlaff 1962, Wolfe 1973). Consequently, active dunes and large blowouts are less common now.

These grasslands provide excellent summer forage and need careful management to prevent grazing out desirable species. Overgrazing also kills out desirable shrubs, especially Amorpha canescens and Prunus pumila var. besseyi (Ryan et al. 1994). These grasslands often respond rapidly to management. Deferment of grazing in the late spring and summer generally favors warm-season grasses such as Andropogon hallii, Bouteloua gracilis, Calamovilfa longifolia, and Schizachyrium scoparium. Drought also causes declines in cover of all species, especially tall grasses, and can make the grassland more vulnerable to blowouts. Grazing during droughts increases the intensity of the damage (Ramaley 1939a, b). Many of these stands, especially those disturbed by wind and grazing, are vulnerable to invasion by exotic annual species of Brome (Comer et al. 1999).

Grazing should be managed to avoid instigation and perpetuation of blowouts and vegetation loss within this system. Prescribed fires can also be used to enhance, maintain and restore these sites.

In addition to reestablishing ecological processes such as prescribed fire, some restoration sites may require the reintroduction of native dominant grass species such as prairie sandreed, sand bluestem and needle and thread. Restoration efforts should utilize seed sources collected from nearby sand prairie remnants to augment and maintain genetic diversity of isolated, remnant plant populations.

S. Mincemoyer, T. Luna and L. Vance

12/4/2024