Shallow

Description

The Reference State represents the best estimate of the natural range of variability that dominated the dynamics in this ecological site prior to European settlement. This site, in the Reference State, is dominated by warm-season grasses and subdominant cool-season grass. Forbs will be common and diverse, shrubs species will vary depending on precipitation, and slope aspect. Ponderosa pine and Rocky Mountain juniper can occur naturally on steep slopes and ridges adjacent to rock outcrops. Grazing or the lack of grazing, fire, and drought are the major drivers between plant communities.

Submodel

Description

The Shortgrass State is dominated by warm-season shortgrass species and upland sedges. This State is the result of grazing management that does not provide adequate recovery time for tall- and mid-statured warm- and cool-season grasses. The hydrologic function of this state may be altered. Runoff is high, and infiltration is low. The Shortgrass State is very resistant to change through grazing management alone.

Submodel

Description

The Early Successional State is dominated by weedy annuals and biennials, sand dropseed, threeawn, and field sagewort (green sagewort). This State is the result of heavy disturbance such as frequent and severe defoliation or heavy livestock concentrations coupled with grazing management that does not provide adequate time for recovery in the Reference State (1.0).
It can also be the result of a high-intensity fire and subsequent soil erosion in the Conifer State (3.0).
The hydrologic function is also likely to be dramatically altered. Runoff is high, and infiltration is low. The Early Succesional State is very resistant to change through grazing management alone.

Submodel

Description

The Conifer State occurs when ponderosa pine, Rocky Mountain juniper, or eastern red cedar become established or expand on this site. As conifer canopy cover increases, the herbaceous component will decrease, bare ground increases and pine needles build up and create a thick duff layer. As competition from herbaceous species decrease, conifers can establish more readily under the canopy. Heavy grazing can contribute to this transition, but it may also occur independently without human influence other than through fire suppression.

The Pine Ridge area of Nebraska is drier than the Black Hills (MLRA 62) where expansive stands of ponderosa pine occur, and pine regenerates readily following fire. Nebraska is not an area where ponderosa pines thrive as the state is at the southern and eastern edge of ponderosa pine range (Gaarder, 2013). Replanting is difficult because of the limited growing conditions for the species in Nebraska. Previous efforts to replant ponderosa pine in burned areas of northwest Nebraska, notably near Fort Robinson State Park (Gaarder, 2013), Chadron State Park, and East Ask Creek watershed have been largely unsuccessful (Nebraska Forest Service, 2013).

It would not appear that MLRA 64 has consistent climatic conditions necessary for ponderosa pine germination and regeneration. Those conditions may be episodic as they are in the drier American southwest. Regeneration of ponderosa pine in New Mexico and Arizona are strongly episodic and the basis of these pulses are at least partly controlled by climate. Ponderosa pine in the Southwest require a warm wet spring and an above-average water supply throughout the year for germination to occur and seedlings to establish. One study from northern Arizona showed a large cohort of ponderosa pine that established within a two-year period between 1919 and 1920 when optimal combination of temperature and precipitation factors occurred. This episodic event was not repeated for 73 years (Savage, M., et al, 1996).

The Conifer State on the Shallow ecological sites may be limited in extent, especially those plant communities having large ponderosa pine components. As high intensity, medium to large sized wildfires occur, these plant communities may become less common as grassland communities replace these woodlands.

Submodel