DUNES 6-10 P.Z.

Description

The reference state is representative of the natural range of variability under pristine conditions. The reference state has three general community phases; a perennial grass dominant phase, a shrub-grass dominant phase and a shrub dominant phase. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Plant community phase changes are primarily driven by fire, periodic drought and/or insect or disease attack.

Submodel

Description

This state is characterized by the presence of non-native invasive species in the understory. This state is similar to the Reference State (1) and has the same three general community phases. Ecological function has not changed, however, the resiliency of the state has been reduced by the presence of invasive weeds. Prescribed grazing and infrequent fire maintains state dynamics. These non-natives are highly flammable and can promote wildfire where fires historically have been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include the non-natives high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate and adaptations for seed dispersal.

Submodel

Description

This state has crossed a biotic threshold and site processes (soil hydrology, nutrient cycling, and energy capture) are being controlled by the shrub component of the plant community. Perennial bunchgrass may or may not be present in trace amounts. The herbaceous understory is dominated by annual non-native species such as cheatgrass and mustards. Resiliency has declined and further degradation from fire facilitates a cheatgrass and sprouting shrub plant community. Fire return interval has shortened due to the dominance of cheatgrass in the understory and is a driver in site dynamics. Sagebrush may be eliminated by continued fire. Spiny hopsage and ephedra may resprout if grazing is controlled and drought does not occur following fire. Negative feedbacks enhance ecosystem resilience and contribute to stability of this state. These include the persistent seedbank and competitive ability of cheatgrass.

Submodel

Description

This state has two community phases, with the primary phase (4.1) dominated by non-native annuals characterized by frequent fire. This state has crossed both a biotic and abiotic threshold. Annual non-native species, including cheatgrass, mustards and Russian thistle, dominate the plant community. Sprouting shrubs may be present in trace amounts; sagebrush is missing. Ecological processes are controlled by the non-native annual community during the spring growing season and by the physical process of wind movement of soil after the annual plant cover has senesced. In extremely degraded sites, wind erosion of soil may progress to dune formation or flattening (depending on landscape position) and near elimination of the annual plant community. Negative feedbacks contributing to the stability of this state include the persistence of non-natives and competition from non-natives for soil moisture and nutrients prevent recruitment of native species. Fine fuels provided by non-native annuals support a fire regime that is often too frequent for the successful establishment of sagebrush and favor an increase in non-native invasive annuals, however if time between fires is long enough sagebrush can return although this is a rare occurrence it is possible.

Submodel