Pumice North 8-10 PZ

Description

The Reference state 1.0 is a representative of the natural range of variability under pristine conditions. The Reference State has 3 general community phases; a shrub-grass dominant with scattered old growth western juniper phase, a perennial grass dominant phase and a shrub-western juniper 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.

Dominant plant species

1. western juniper (Juniperus occidentalis), tree

2. mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub

3. Idaho fescue (Festuca idahoensis), grass

4. bluebunch wheatgrass (Pseudoroegneria spicata ssp. spicata), grass

Submodel

Description

This state is similar to the Reference State 1.0 with three similar community phases. Ecological function has not changed; however, the resiliency of the state has been reduced by the presence of invasive weeds. Non-natives may increase in abundance but will not become dominant within this State. These non-natives can be highly flammable and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These feedbacks 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, residual dry matter accumulation, and adaptations for seed dispersal.

Dominant plant species

1. western juniper (Juniperus occidentalis), tree

2. mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub

3. Idaho fescue (Festuca idahoensis), grass

4. bluebunch wheatgrass (Pseudoroegneria spicata ssp. spicata), grass

Submodel

Description

This state is a product of many years of heavy grazing during time periods harmful to perennial bunchgrasses, changes in the historic fire regime or long-term drought favoring shrub establishment. Grazing tolerant Sandberg bluegrass will increase with a reduction in deep rooted perennial bunchgrass competition and become the dominant grass. Sagebrush dominates the overstory and rabbitbrush may be a significant component. Sagebrush cover exceeds site concept and may be decadent, reflecting stand maturity and lack of seedling establishment due to competition with mature plants. The shrub overstory and Sandberg bluegrass understory dominate site resources such that soil water, nutrient capture, nutrient cycling and soil organic matter are temporally and spatially redistributed (3.1). In both community phases, bare ground may be significant with soil redistribution occurring between interspace and shrub locations. Western juniper increases and may begin to influence the understory vegetation.

Dominant plant species

1. western juniper (Juniperus occidentalis), tree

2. mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub

3. rabbitbrush (Chrysothamnus), shrub

4. Sandberg bluegrass (Poa secunda), grass

Submodel

Description

This state is characterized by the dominance of annual non-native species such as cheatgrass and tansy mustard (Descurainia pinnata) in the understory. Old growth juniper is present but scattered. Depending on transition, young juniper may be increasing. Sagebrush and/or rabbitbrush may dominate the overstory.

Dominant plant species

1. cheatgrass (Bromus tectorum), grass

Submodel

Description

This state is characterized by a dominance of young juniper (less than 100 years old) in the overstory. Sagebrush and perennial bunchgrasses may still be present, but they are no longer controlling site resources. Soil moisture, soil nutrients and soil organic matter distribution and cycling have been spatially and temporally altered.

Dominant plant species

1. western juniper (Juniperus occidentalis), tree

Submodel