Ecological dynamics
It is impossible to determine in any quantitative detail the Historic Climax Plant Community (HCPC) for this ecological site because of the lack of direct historical documentation preceding all human influence. In some areas, the earliest reports of dominant plants include the cadastral survey conducted by the General Land Office, which began in the late 19th century for this area (Galatowitsch 1990). However, up to the 1870s the Shoshone Indians, prevalent in northern Utah and neighboring states, grazed horses and set fires to alter the vegetation for their needs (Parson 1996). In the 1860s, Europeans brought cattle and horses to the area, grazing large numbers of them on unfenced parcels year-long (Parson 1996). Itinerant and local sheep flocks followed, largely replacing cattle as the browse component increased.
Below is a State and Transition Model diagram to illustrate the “phases” (common plant communities), and “states” (aggregations of those plant communities) that can occur on the site. Differences between phases and states depend primarily upon observations of a range of disturbance histories in areas where this ESD is represented. These situations include grazing gradients to water sources, fence-line contrasts, patches with differing dates of fire, herbicide treatment, tillage, etc. Reference State 1 illustrates the common plant communities that probably existed just prior to European settlement.
The major successional pathways within states, (“community pathways”) are indicated by arrows between phases. “Transitions” are indicated by arrows between states. The drivers of these changes are indicated in codes decipherable by referring to the legend at the bottom of the page and by reading the detailed narratives that follow the diagram. The transition between Reference State 1 and State 2 is considered irreversible because of the naturalization of exotic species of both flora and fauna, possible extinction of native species, and climate change. There may have also been accelerated soil erosion.
When available, monitoring data (of various types) were employed to validate more subjective inferences made in this diagram.
State 1
Reference State
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 least modified plant community would have been a tall shrub-dominated community with occasional Rocky Mountain juniper (Juniperus scopulorum), and a rich and productive understory of graminoids and forbs (1.1). Dominant shrubs would have included alderleaf mountain mahogany (Cercocarpus montanus), Utah serviceberry (Amelanchier utahensis), along with the associated shrubs mountain big sagebrush (Artemisia tridentata ssp. vaseyana), mountain snowberry (Symphoricarpos oreophilus), and antelope bitterbrush (Purshia tridentata). Primary grasses would have included bluebunch wheatgrass (Pseudoroegneria spicata), sheep fescue (Festuca ovina), mountain brome (Bromus marginatus), and Columbia needlegrass (Achnatherum nelsonii). Dominant forbs would have included arrowleaf balsamroot (Balsamorhiza sagittata), tailcup lupine (Lupinus caudatus ssp. caudatus), and longleaf phlox (Phlox longifolia) among others. 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 document. Wildfires would have maintained a balance between woody and non-woody vegetation, as many of the primary shrub species are root-sprouters and respond quickly following fire.
Community 1.1
Alderleaf mountain mahogany, Utah serviceberry & other tall shrubs/ scattered Rocky Mountain juniper/ rich & productive herbaceous understory
This plant community would have been characterized by tall shrub-dominated vegetation, primarily alderleaf mountain mahogany and Utah serviceberry, with scattered Rocky Mountain juniper, and a rich and productive native perennial herbaceous understory. Other associated shrubs would have included mountain big sagebrush, mountain snowberry, and antelope bitterbrush. Understory grasses would have included bluebunch wheatgrass, sheep fescue, and Columbia needlegrass. Dominant forbs would have included arrowleaf balsamroot, tailcup lupine, and longleaf phlox among others.
State 2
Alderleaf Mountain Mahogany/ Utah Serviceberry/ Introduced Non-natives State
State 2 is a description of the ecological site shortly following Euro-American settlement, which has been influenced by the introduction of several non-native plants and animals, possible extinctions of native species, and a different climate. The plant community will be very similar to State 1 with the exception that some introduced species are likely to be present. This state can be regarded as the current potential. The site is dominated by a mixture of tall shrubs including alderleaf mountain mahogany, Utah serviceberry, mountain big sagebrush, mountain snowberry, antelope bitterbrush and scattered Rocky Mountain juniper. A rich and productive native perennial herbaceous understory will also be present (2.1). Because of the steepness of these sites, the vegetation was not heavily used by cattle and horses. However, herding of sheep was quite prevalent during the first half of the 20th Century. This vegetation was and still remains a favorite of big game. Because these classes of animals focus on browse, the understory is more intact than less steep nearby sites. Wildfires are important in rejuvenating the woody component, as the majority of the shrubs on these sites respond and recover rapidly following fire. Because soils on this site are rocky, they are considered “self armoring,” thus making the site resistant to the effects of erosion. Another factor contributing to the resiliency of this state is that the most desirable species are long-lived and are root-sprouters. Resiliency, however, will be reduced by excessive utilization which results in insufficient regeneration of the desirable species. Without regeneration of desirable species, some populations over-mature making them susceptible to catastrophic, sudden losses, and as a result unpalatable invaders can take over the site.
Community 2.1
Alderleaf mountain mahogany, Utah serviceberry & other tall shrubs/ scattered Rocky Mountain juniper/ rich & productive herbaceous understory
This plant community is characterized by a mixture of tall shrubs including alderleaf mountain mahogany, Utah serviceberry, mountain big sagebrush, mountain snowberry, antelope bitterbrush and scattered Rocky Mountain juniper. The understory is composed of grasses including bluebunch wheatgrass, sheep fescue, and Columbia needlegrass. Dominant forbs would include arrowleaf balsamroot, tailcup lupine, and longleaf phlox among others.
State 3
Taller Shrubs/ Rocky Mountain Juniper State
Lengthening of the fire cycle directly through fire control and indirectly through heavy livestock grazing reduces the fine fuels, ultimately tipping the balance toward woody plants and increasing the proportion of non-sprouters such as Rocky Mountain juniper and mountain big sagebrush (3.1). Because soils on this site are rocky they are considered “self armoring,” thus making the site resistant to the effects of erosion. The state will maintain stability with cool season fires, whereas hot summer fires are likely to reduce state stability.
Community 3.1
Taller shrubs/ increased juniper & mountain big sagebrush/ reduced herbaceous understory
This plant community is characterized by taller, denser shrubs, including the non-sprouting species such as Rocky Mountain juniper and mountain big sagebrush. The herbaceous understory is diminished due to heavy livestock grazing during the growing season of grasses.
State 4
Shorter Shrubs/ Increased Seeded Herbs State
State 4 is dominated by shorter, mostly re-sprouting shrubs, and an herbaceous understory composed of both native and introduced perennials. Native shrubs include mountain big sagebrush and yellow rabbitbrush (Chrysothamnus viscidiflorus). Wildfire or prescribed burning followed by a period of grazing deferment will provide a balance between woody and non-woody plants. If increased grazing is allowed too soon after fire, introduced species may dominate the understory (4.1). This state will lose stability with the increase in exotics and the loss of native herbs and grasses.
Community 4.1
Shorter & fewer shrubs/ reduced juniper & mountain big sagebrush/ increased herbaceous understory
This plant community is dominated by re-sprouting shrubs, such as yellow rabbitbrush, with an understory of grazing-tolerant native herbs and invaded herbs, such as arrowleaf balsamroot.
Transition T1A
State 1 to 2
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.
Transition T2A
State 2 to 3
Heavy utilization primarily by sheep and occasionally by cattle and horses during the first half of the 20th century, combined with fire suppression, reduced much of the understory and allowed the shrubs to take over the site. Big game then hedged and high-lined the remaining shrubs. The survivors are all taller with the canopies having a marked browse line.
Transition T3A
State 3 to 4
Prescribed burning or wildfire accompanied by aerial seeding, followed by grazing deferment, offers the only logical way to proactively promote a more diverse state with a better balance between woody and non-woody plants. Shrubs will be shorter, with non-sprouting species temporarily be reduced. Fire may potentially produce an increase in invasive herbs. If increased grazing is allowed too soon after fire, introduced species are given an additional advantage. A key indicator of the approach to this transition is the build up of fuels, and fire is the trigger for the transition. Because of steep slopes on this site, a restoration pathway is impracticable.
