LOAMY 8-10 P.Z.

Description

The reference state is representative of the natural range of variability prior to Euro-American settlement conditions. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. The reference state has three general community phases a perennial grass dominant phase, a perennial grass-shrub mixture and a shrub-dominant phase. Disturbance favors the grass-dominated and grass-shrub phases and less frequent disturbance favors the shrub-dominated phase. Community phase changes are primarily driven by time, infrequent wildfires, periodic drought and insect or disease attack.

Submodel

Description

State 2 This state is similar to the Reference State (1) and the same three community phases occur. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of non-native invasive species (5-15% by weight). Low frequency and low intensity disturbances favor the grass-dominant and grass-shrub mixture phases but the presence of non-natives is favored if frequency and severity of disturbances change from historic conditions. Prescribed grazing and infrequent fire (50-100 year return interval) maintain state dynamics. Prescribed grazing and/or release from drought may reverse declines in Thurber’s needlegrass and Indian ricegrass production.

Submodel

Description

State 3. State 3 has two community phases. One phase is a dense overstory of decadent Wyoming big sagebrush and an understory of Sandberg's bluegrass, a shallow-rooted cool season perennial bunchgrass. The second community phase is dominated by Sandberg’s bluegrass with non-native annuals in the plant community. A trace of deep-rooted perennial bunchgrasses remains in the plant community. Non-native annual grasses and forbs are abundant in the understory. A biotic threshold has been crossed and site resiliency has been reduced with the loss of the deep rooted perennial bunchgrasses. Feedbacks contributing to the stability of this state include the loss of structural and functional groups (deep-rooted perennial bunchgrasses and shrub seedlings), resulting in decreased herbaceous production and reduced organic matter inputs. Changes in infiltration and runoff rates contribute to reduced soil moisture availability thereby reducing reproductive potential of native species.

Submodel

Description

State 4. State 4 has two community phases. One phase is dominated by non-native annual species, primarily cheatgrass, halogeton, Russian thistle, fiddleneck, and annual mustards. Sandberg's bluegrass and squirreltail may also occur. The second community phase is dominated by fire tolerant shrubs and non-native annuals. An abiotic threshold has been crossed and state dynamics are now driven by fire and time. The length of time between fires creates two potential community phases with broom snakeweed and rabbitbrush increasing with fire return intervals >10 years. This alternative stable state is persistent due to strong feedbacks, including presence of non-natives; competition from non-native species for soil moisture and nutrients prevent germination and establishment of native species. Fine-fuel loading supports a modified fire regime too narrow for the successful establishment of Wyoming big sagebrush and favors an increase of non-native invasive annuals. Biogeochemical cycling is altered by dominance of cheatgrass modifying the soil environment. Cheatgrass monocultures have low VAM fungal populations, increasing the difficulty of reestablishing sagebrush and native bunchgrasses that require these mycorrhizae.

Submodel

Description

The seeded state that has three community phases; a grass dominated phase, a shrub-grass co-dominated phase and a shrub phase. The seeded species may be native or non-native. Annual non-native species may also be present. Following wildfire, range plantings help to stabilize the soil surface, reduce erosion and provide competition for non-native annuals. Seeded species may include native and non-native species. Annual non-natives may be present. Typically there is an overall lack of native perennial forbs. However, some seeded forbs, like western yarrow (Achillea millefolium), may do quite well. Feedbacks contributing to the stability of this state include competitive ability and vigor of seed species. Seeded perennial grasses reduce the availability of critical resources to non-native annuals, reducing fire frequency.

Submodel