Mound - Intermound Complex

Mechanism

Transitions for Very Shallow component:
T1 Result: Shift from Reference State Community Phase 1.1 to Community Phase 2.1, resulting in the shift of functional groups to forbs and/or invasive annual grasses.

Primary Trigger: Extensive spring grazing with heavy use to Sandberg bluegrass. Plant vigor declines and most or all Sandberg bluegrass plants are lost from the community. The soil is more open to evaporation, to wind and water erosion, and facilitates plant community changes from Community 1.2 to Community 2.1.

Secondary Triggers: a micro-burst of cheatgrass could put Community 1.2 at risk. The trampling of Very Shallow soils, displacing and disturbing the surface soil structure by grazing animals could also trigger transition to State 2.

Ecological process: mortality of Sandberg bluegrass frees resources in the surface soils that allows native forbs to increase, while introduced annual species (forbs and grasses) colonize and expand. A micro-burst of annual grasses could allow even pristine sites to be invaded. Community 1.2 is the community most at risk and is also the pathway for crossing the threshold from State 1 to State 2.

Indicators: Declining vigor and cover of Sandberg bluegrass, declining soil biotic crust and, increasing gaps between perennial bunchgrasses.


Transitions for Loamy Mound component:
T1 Result: Shift from Loamy Mound Community 1.2 across a threshold to Community 2.1, which is dominated by annual grasses.

Ecological process: Generally, with grazing activity livestock trail across Very Shallow component to graze the Loamy Mound component. Very Shallow receives minimal grazing while the Loamy Mound can be grazed heavily. As grazing increases livestock trails are evident on the Very Shallow, but the Loamy Mounds are hammered.

Primary trigger on Loamy Mound: heavy soil disturbances from rodents/rabbits &/or heavy grazing pressure from rodents, rabbits or livestock (heavy to severe grazing intensity, chronic critical period grazing or season long grazing). Mortality of bunchgrasses occur (basin wildrye, bluebunch wheatgrass and Idaho fescue. As bunchgrasses decline, annual grasses and tumble mustard or Russian thistle colonize and eventually become dominant. For mounds with sagebrush, shrubs will increase alongside the annual grasses.

Secondary trigger on Loamy Mounds: Drought cycle coupled with heavy grazing.

Indicators on Loamy Mound: Reduced vigor of bunchgrasses, colonization by annual grasses, increasing canopy gaps for perennials species, increasing sagebrush cover.