Loamy, North Aspect, Grassland

Description

State 1 Narrative:
State 1 represents grassland steppe with no invasive or exotic weed species. Grassland sites have no sagebrush and no bitterbrush. Rabbitbrush is present but a minor species in the reference State. All the functional, structural groups have one or more native species present.

Reference State Community Phases:
1.1 Bunchgrass Idaho fescue – bluebunch wheatgrass
1.2 Bunchgrass – Shrub Idaho fescue – bluebunch wheatgrass – rabbitbrush – rose

Community 1.1 , the reference Community is stable with a high cover of Idaho fescue/bluebunch wheatgrass and low cover of rabbitbrush.

Community 1.2 happens when the dominant bunchgrasses exhibit lower cover. As the bunchgrasses decline the rabbitbrush increases.

Dominant Reference State Species:
Idaho fescue with bluebunch wheatgrass as sub-dominant

At-risk Communities:
• All communities in the reference state are at risk of moving to State 2. The seed source of cheatgrass, chervil and other invasive species is nearby and blowing onto most sites annually
• Any community becomes at-risk of moving to State 3 when Idaho fescue and bluebunch have low vigor and annual bromes have colonized the site
• Any Loamy North Aspect community is at risk when fire kills Idaho fescue plants. The holes could quickly be filled by annual grass or invasive forbs.

Submodel

Description

State 2 Narrative:
Based on opportunity, State 2 is dominated by either introduced forbs or invasive annual grasses. Opportunity refers to what seed in the seedbank and moisture available from year to year. Soil disturbances by rodents or badgers allow invasive species to colonize.

In State 2 bunchgrasses which were dominant in the reference state are virtually missing and the other native, functional-structural groups have been altered.

Community Phases for State 2:
2.1 Introduced Forb - Shrub Yellow star-thistle, etc. – Rabbitbrush
2.2 Annual Grass – Shrub Cheatgrass, etc. – Rabbitbrush


Dominant Species in State 2:
Annual bromes, yellow star-thistle, chervil, rabbitbrush

Pathways within State 2
Result: there is a natural fluctuation between communities 2.1 and 2.2.

Primary Trigger: drier years favor the annual grasses while wetter years favor the introduced forbs/weeds

Ecological process: in State 2 the seedbank of annual grasses and introduced forbs/weeds is full. In any given year one or more invasive species will have the opportunity to expand to become dominant or co-dominant. The next year a different species may have a similar opportunity.

Submodel