High Mountain Loam (silver sagebrush)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1a
introduction of exotic species
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Transition T2a
Heavy continuous season-long grazing along with fire exclusion
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Transition T3a
Brush removal, fire, and grazing deferment
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Transition T3b
Plowing and drill seeding on gentler slopes
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Transition T4a
Heavy, continuous season-long grazing
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Transition T5a
Heavy, continuous season-long grazing
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. The description of the Reference State was determined by NRCS Soil Survey Type Site Location information and familiarity with rangeland relict areas where they exist. The Reference State vegetation would have been a shrub steppe. Dominant shrubs included silver sagebrush (Artemisia cana) and mountain snowberry (Symphoricarpos oreophilus). Snowfield sagebrush (Artemisia spiciformis) may have also been found here. The understory would have been composed of grasses including slender wheatgrass (Elymus trachycaulus), mountain brome (Bromus marginatus), and bluegrass (Poa spp.). Forbs such as sticky purple geranium (Geranium viscosissimum), Nevada pea (Lathyrus lanszwertii), slender cinquefoil (Potentilla gracilis), and buckwheats (Eriogonum spp.) among many others persisted.
The average fire return interval would have ranged from 30 to 50 years, which would have been the driving factor behind changes in abundance of shrubs relative to the associated understory. One community phase would have been an herbaceous-dominant phase (1.1) that would have been found following recent wildfire events (1.2a). As the time since fire increased (1.1a), both the shrubs and herbaceous understory would have increased (1.2). A more complete list of species by lifeform for the Reference State is available in accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this ESD document.
Submodel
Description
State 2 is very similar to State 1 in form and function, with the exception of the presence of non-native plants and animals, possible extinctions of some native species, and a different climate. Nevertheless, a shrub steppe persisted that should be considered the current potential. State 2 is a description of the ecological site shortly following Euro-American settlement. Primary shrubs are silver sagebrush and mountain snowberry. Snowfield sagebrush may also be found here. Grasses include slender wheatgrass, mountain brome, and bluegrass. Forbs include sticky purple geranium, Nevada pea, slender cinquefoil, and buckwheats. A small component of non-native species may also be present such as cheatgrass (Bromus tectorum), common dandelion (Taraxacum officinale), common mullein (Verbascum thapsus), mountain tarweed (Madia glomerata), and houndstongue (Cynoglossum officinale).
Submodel
Description
A thickening of shrubs, particularly of silver sagebrush and snowberry, and a reduction of native forbs was seen following a near-century long period of heavy livestock grazing during growing season of herbs. Introduced forbs such as common dandelion, common mullein, mountain tarweed, houndstongue, and snakeweed (Gutierrezia sarothrae) became abundant in the understory.
Submodel
Description
This state is dominated by perennial forbs (4.1). Shrubs will re-sprout following fire or chemical applications; annuals could be replaced by perennials. If keeping the shrubs back is desirable, re-treatment using fire or chemicals may be necessary (4.1a)
Submodel
Mechanism
The simultaneous introduction of exotic species, both plants and animals, possible extinctions of native flora and fauna, and climate change has caused State 1 to transition to State 2. Reversal of such historic changes (i.e. a return pathway) back to State 1 is not practical.
Mechanism
Heavy continuous season-long grazing between the 1860s and the 1950s, along with fire exclusion policies saw an increase in shrubs and a replacement of the native forb component with introduced forb species. Reduction in cover leads to accelerated soil erosion, lowering of stream channels and thus xerification and distrophication. While this site is not riparian, it is near enough to streams that it is sub-irrigated at the time of snow pack melt-off. This makes it more resilient than the adjacent uplands. If this site is to remain a productive shrub steppe, the vegetation cover should remain extensive enough so as to prevent accelerated soil erosion.
Mechanism
Brush removal by either chemical means (2,4-D), or prescribed fire, and grazing deferment, will convert State 3 into a perennial forb-dominated state.
Mechanism
Plowing and drill seeding on gentler slopes will increase forage production potential by conversion to introduced grasslands (e.g. intermediate wheatgrass (Thinopyrum intermedium), smooth brome (Bromus inermis), and orchardgrass (Dactylis glomerata)).
Mechanism
Heavy, continuous season-long grazing will return this State 5 to State 3, a thickened shrub and introduced forbs state.
Model keys
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