Northern Great Plains Shrubland

This ecological system ranges from South Dakota into southern Canada on moderately shallow to deep, fine to sandy loam soils. These sites are typically more mesic than most of the surrounding area. This system may be located along upper terraces of rivers and streams, gently inclined slopes near breaklands, and upland sandy loam areas throughout its range. This system is dominated by shrub species such as Amelanchier alnifolia, Rhus trilobata, Symphoricarpos spp., Shepherdia argentea, Crataegus douglasii, Elaeagnus commutata, Dasiphora fruticosa ssp. floribunda, and dwarf-shrubs such as Juniperus horizontalis. Midgrasses such as Festuca spp., Koeleria macrantha, and Pseudoroegneria spicata and species such as Carex filifolia can co-occur. This system differs from Northwestern Great Plains Mixedgrass Prairie (CES303.674) in that it contains greater than 10% cover in conjunction with topographic relief (breaks) of natural shrub species. Fire and grazing constitute the primary dynamics affecting this system; drought can also impact this system. This system may include areas of Northwestern Great Plains Mixedgrass Prairie (CES303.674) where fire suppression has allowed for a greater cover of shrub species. This system is similar to Northern Rocky Mountain Montane-Foothill Deciduous Shrubland (CES306.994) but occurs in the grassland matrix of the Great Plains, whereas the Rocky Mountain system occurs adjacent to the lower treeline of generally forested mountains and highlands. Floristically their shrub composition is similar, but associated grasses and forbs will differ somewhat given their respective adjacent vegetation types.

This system is dominated by shrub and dwarf-shrub species such as Amelanchier alnifolia, Rhus trilobata, Symphoricarpos spp., Dasiphora fruticosa ssp. floribunda, and Juniperus horizontalis. Mid grasses such as Festuca spp., Koeleria macrantha, and Pseudoroegneria spicata can also occur. This system differs from Northwestern Great Plains Mixedgrass Prairie (CES303.674) in that it contains greater than 60% cover of natural shrub species.

Climate and growing season length for the region this system occurs are intermediate to the shortgrass regions to the west and the tallgrass regions to the east with a shorter growing season with semi-arid moisture conditions. This system occurs on sites more mesic than most of the surrounding area such as upper river terraces, gently inclined slopes, and upland sandy areas. Soils range from shallow to deep and fine to sandy loams.

Fire and grazing constitute the primary dynamics affecting this system. Drought can also impact this system.

LANDFIRE developed a state-and-transition vegetation dynamics VDDT model for this system which has three classes in total (LANDFIRE 2007a, BpS 2010850). These are summarized as:

A) Early Development 1 Open (herbaceous-dominated - 35% of type in this stage): Cover is 0-50%. Grasses such as little bluestem, western wheatgrass, stipa, bluebunch wheatgrass, sideoats grama and upland sedges dominate this class. This class is a combination of grasses and very short-statured vegetation resulting also from prairie dog disturbance (maybe only in draws - snowberry). A variety of forb species such as fetid marigold, scarlet globemallow, scarlet gaura, skeleton weed and dotted gayfeather tend to dominate this class. Some sprouting of snowberry, chokecherry and serviceberry. The fuel in this class would be initially too sparse to carry fire, but then fuel increases. This class lasts for 9 years then succeeds to class B, mid-open state. (Although, if it were a dense stand initially and then re-sprouted, might take fewer than 9 years to get to class B.) Replacement fire occurs every 30 years, and sets this class back to its beginning stage. Grazing (0.07 probability or 7% of this class each year), the combination of drought and grazing (0.02 probability or 2% of this class each year) and drought modeled as wind/weather/stress (0.05 probability or 5% of this class each year) all occur and maintain this class but don't set it back to its beginning state. Prairie dog impact occurs with a probability of 0.0035 (0.35% of class each year) and returns this class to its beginning. The only shrub that prairie dogs might impact in this BpS would be the snowberry sites and draws/drainageways.

B) Mid Development 1 Open (shrub-dominated - 25% of type in this stage): Shrub cover is 0-20%. More open community than late stage. Seedling shrubs. Dominant shrubs coming in include snowberry, chokecherry, skunkbush, creeping juniper and buffaloberry. Western wheatgrass, needlegrasses, little bluestem and upland sedges are common grasses - same as in class A. Bluebunch wheatgrass can be locally common with skunkbush. Common forbs include scurfpea, prairie coneflower, Rocky Mountain beeplant, scarlet globemallow and dotted gayfeather. Herbaceous cover is approximately 30-70% and approx. 0.5 m in height. This class lasts 9 years and then succeeds to the late-development stage. Replacement fires occur every 30 years. Grazing (0.02 probability or 2% of this class each year) and the combination of drought and grazing (0.01 probability) occur and cause a transition back to the early stage, class A. Grazing (0.02 probability), the combination of drought and grazing (0.003 probability) and drought modeled as wind/weather stress (0.1 probability) can also occur while maintaining this class in this stage. Prairie dog impact occurs with a probability of 0.0003, taking the class back to class A.

C) Late Development 1 Closed (shrub-dominated - 40% of type in this stage): Tree cover is 21-80%. Denser, higher canopy cover. Mature canopy. Vegetation community is similar to previous class. Forbs are present still. Litter layer tends to be relatively continuous. Herbaceous cover 50-65% and 0.5 m in height. Snowberry average cover could be 65%. Maximum up to 75%, minimum approx. 45%. Skunkbush cover average approximately 25%. Horizontal juniper average 44%, range of 25-65% cover. Each of the shrub species associated with own habitat type with moisture gradient. Skunkbush is dry end, and snowberry/chokecherry is wet end.

The northern mixed-grass prairie and shrublands are strongly influenced by wet-dry cycles. Fire, grazing by large ungulates and small mammals such as prairie dogs and soil disturbances (i.e., buffalo wallows and prairie dog towns) are the major disturbances in this vegetation type. In MZ30, many of these shrubland types occur on moderate to steep slopes (west- to northwest-facing).

From instrumental weather records, droughts are likely to occur about 3 in every 10 years. Historically, there were likely close interactions between fire and grazing since large ungulates tend to be attracted to post-fire communities. Conversely, fire presumably was less likely in areas recently heavily grazed by herbivory, thus contributing to spatial and temporal variation in fire occurrence.

Average fire intervals are estimated at 8-25 years, although in areas with very broken topography fire intervals may have been greater than 30 years. The model for MZ20 reflects a 30-year FRI. This system's FRI should be very similar to 1141 mixedgrass prairie, since this system is just inclusions within 1141. It might be a little less frequent because of moisture; however, it should be similar.

Fires were most common in July and August, but probably occurred from about April to September. Seasonality of fires influences vegetation composition. Early-season fires (April - May) tend to favor warm-season species, while late-season fires (August - September) tend to favor cool-season species. Replacement fire in our model does remove 75% of the above-ground cover as assumed in the literature. However, loss of the above-ground cover by the replacement fire will not necessarily induce a retrogression back to an earlier seral stage from the late stage because the main component of dominant grasses remains unharmed to insure the continuity of the seral stage. The shrub species, however, are sprouters. Fire would remove them, and they would resprout. The exception would be horizontal juniper and skunkbush which would not resprout. It would take longer for them to become re-established.

Different levels of native ungulate grazing intensities were used in LANDFIRE modelling. Light grazing was assumed to not alter the community enough to change classes but increasing grazing intensity would move the community back to earlier stages. Grazing return interval probably occurred every 7-10 years but grazing would only result in a class change maybe once every 80-100 years. Overall, the grazing frequency was modeled at every 20 years - that includes grazing just occurring with no transition resulting, as well as grazing taking the stage back to an earlier class. And, overall, the drought plus grazing impact frequency was modeled as every 70 years - that includes the no-transition plus transition to early stage (LANDFIRE 2007a, BpS 2010850). In addition to fire, drought, grazing and insect outbreaks (Rocky Mountain locust) would have impacted all classes, historically.

Conversion to agriculture can impact this system, and its range has probably been decreased by human activities. Impacts from energy extraction in oil and gas fields in the Dakotas and eastern Montana have recently fragmented large areas with road networks to well pads and pipelines. Livestock grazing and trampling can negatively impact these shrublands, especially during the winter as stands often occur in swales and stream terraces that offer livestock and wildlife some protection from winter storms.

This system extends from South Dakota into southern Canada, west into the foothills of north-central Montana. The U.S. range corresponds to Bailey et al. (1994) sections Northeast Glaciated Plains (332A), Western Glaciated Plains (332B), North Central Glaciated Plains - extreme western part (251B), and in Canada to the Moist Mixed Grassland and Fescue Grassland.