State 1
Reference

This state represents the natural variability and dynamics of this ecological site, prior to European settlement. The dominant aspect of this site is Pinyon and Utah Juniper with an understory of shrubs and associated grasses. The primary disturbance mechanisms for this ecological site in reference condition include drought, insects, and infrequent fire. Because catastrophic disturbances like a crown fire or drought happen with long intervals, these communities have long periods of succession (i.e. long periods of dense Pinyon and Juniper) of 300 to 600 years in upland ecological sites within the foothills, and 300 to 1,000 in semi-desert ecological sites. The timing of drought, and fire, coupled with surface disturbance can dictate whether the community can stay within the reference state or if the community transitions into another state. Fluctuations in species composition and relative production may change from year to year dependent on climatic factors. At the lower end of precipitation and elevation ranges the deciduous shrubs (gambel oak, alderleaf mountain mahogany and wild crab apple) will be less abundant in the understory and will be more abundant at the higher precipitation and elevations, and north and east slopes. Winterfat and fourwing saltbush will be found predominantly at the lower elevations, lower precipitation, and on south and west facing slopes.

Community 1.1
Pinyon-Juniper Woodland

When the tree canopy cover increases to 15 to 35 percent, the same plants are present; however, the amounts of grasses and shrubs have decreased. Pinyon and Utah juniper trees have increased and are larger in size. At this stage Utah juniper may be dominant over Pinyon. Pinyon trees are more susceptible to drought, insects, and disease than Utah Juniper trees. In fact, it is difficult to identify methods beside fire that naturally reduce Utah juniper. After long periods of drought weaken the Pinyon trees, beetle kills can become quite extensive, especially after the droughts. Drought periods can also weaken and reduce the understory. Plant establishment is mainly limited by the available moisture. Total annual production: In an average year, the approximate total annual production (air-dry) is as follows: Tree canopy cover of 0 to 15 percent is 300 to 525 pounds per acre. Grass and grass-likes have approximately 8 percent canopy cover and 5 percent basal area cover with an average height of 1 foot. Forbs have approximately 1 percent canopy cover and 1 percent basal area cover with an average height of 0.5 foot. Shrubs have approximately 1 percent canopy cover and 1 percent basal area cover with an average height of 2 feet. Trees have approximately 20 percent canopy cover and 3 percent basal area cover with an average height of 8 feet.

Community 1.2
Mature Pinyon-Juniper Woodland

As tree canopy cover increases to greater than 35 percent, the trees become dominant, and are larger in size. The tree size and density is directly correlated to precipitation. There is almost no understory production at all. Mature pinyon and Utah juniper woodland characterized this community phase. When weather patterns favor an increase of pinyon and Utah juniper canopy with the associated understory of shrubs, grasses and forbs. Canopy cover may increase to the point where understory vegetation is completely shaded out. Total annual production: In an average year, the approximate total annual production (air-dry) is as follows: Tree canopy cover of 0 to 15 percent is 100 to 450 pounds per acre Grass and grass-likes have approximately one percent canopy cover and one percent basal area cover with an average height of one foot. Forbs have approximately one percent canopy cover and one percent basal area cover with an average height of half foot. Shrubs have approximately 1 percent canopy cover and 1 percent basal area cover with an average height of 1.5 feet. Trees have approximately 40 percent canopy cover and 12 percent basal area cover with an average height of 12 feet.

Community 1.3
Perennial Shrubland with Scattered Pinyon-Juniper

This community phase is grassland with scattered pinyon and Utah juniper. The herbaceous understory has a mix of grasses and forbs. This community phase is a result of a crown fire or sufficiently large and hot ground fire that will kill many of the trees, combined with sufficient seed-banks and moisture for reestablishment of grasses and forbs. It is common that after a crown fire many patches of trees will remain unburned, because of fire’s unpredictability and broken topography. This leaves a seed bank for the burned areas. This community phase is very short lived in comparison to the other community phases in this state. Sparse invasive introduced plants species would be present in this phase. When the tree canopy cover is less than 15 percent, grasses and shrubs coexist with scattered pinyon and Utah juniper. Grasses include bottlebrush squirreltail, western wheatgrass, Indian ricegrass, Sandberg bluegrass, needle and thread, prairie Junegrass, sand dropseed, muttongrass, and Wyoming big sagebrush. Common forbs include fernleaf biscuitroot, rock goldenrod, longleaf phlox, threadleaf ragwort and heartleaf twistflower. Shrubs, half-shrubs, and trees that occur on this site are yellow rabbitbrush, Wyoming big sagebrush, true mountain mahogany, Utah serviceberry, Utah juniper, and two-needle pinyon. As elevation and moisture increase, Utah juniper gives way to pinyon. Total annual production: In an average year, the approximate total annual production (air-dry) is as follows: Tree canopy cover of 0 to 15 percent is 350 to 600 pounds per acre Grass and grass-likes have approximately 15 percent canopy cover and 10 percent basal area cover with an average height of 1 foot. Forbs have approximately one percent canopy cover and one percent basal area cover with an average height of a half foot. Shrubs have approximately two percent canopy cover and one percent basal area cover with an average height of 3.5 feet. Trees have approximately 10 percent canopy cover and less than 1 percent basal area cover with an average height of 5 feet.

Pathway 1.1A
Community 1.1 to 1.2

Pinyon-Juniper Woodland

Mature Pinyon-Juniper Woodland

This pathway occurs when events create a wetter climate cycle, favoring pinyon and perennial bunchgrass establishment. Following several favorable precipitation years and lack of surface disturbances, native perennial plants will reestablish.

Pathway 1.1B
Community 1.1 to 1.3

Pinyon-Juniper Woodland

Perennial Shrubland with Scattered Pinyon-Juniper

This pathway occurs during and after events such as fire, drought or insect and pathogen outbreaks. Droughts and insects weaken and eventually kill the tree cover, allowing an increase in grasses and forbs in the short term, until juniper and pinyon recover. Vegetation manipulation can be used to remove trees and mimic the natural disturbance regime. Fire events leading to this pathway include 1) an understory burn allowed after several wet years of fine fuels accumulated, or 2) crown fires supported by late successional growth of pinyon and juniper with dense crown cover.

Pathway 1.2A
Community 1.2 to 1.1

Mature Pinyon-Juniper Woodland

Pinyon-Juniper Woodland

This pathway occurs during and after events such as fire, natural disturbances, drought or insect and pathogen outbreaks. Droughts and insects weaken and eventually kill the tree cover, increasing nutrient availability in the system. The natural conditions of drought limit the grasses ability to utilize the additional nutrients for a sustained period of time. Grasses and forbs increase initially in the community, but as the juniper and pinyon recover, the grasses and forbs diminish. Small patch fires from lightning strikes are typical of this pathway rather than large scale fires.

Pathway 1.2B
Community 1.2 to 1.3

Mature Pinyon-Juniper Woodland

Perennial Shrubland with Scattered Pinyon-Juniper

This pathway occurs during and after events such as fire, drought or insect and pathogen outbreaks. Droughts and insects weaken and eventually kill the tree cover, allowing an increase in grasses and forbs in the short term, until juniper and pinyon recover. Vegetation manipulation can be used to remove trees and mimic the natural disturbance regime. Fire events leading to this pathway include 1) an understory burn allowed after several wet years of fine fuels accumulated, or 2) crown fires supported by late successional growth of pinyon and juniper with dense crown cover.

Pathway 1.3A
Community 1.3 to 1.1

Perennial Shrubland with Scattered Pinyon-Juniper

Pinyon-Juniper Woodland

This pathway occurs with a wetter precipitation years and time without disturbance, providing trees the ability to establish and grow. The tree cover reduces the available nutrients and energy for other vegetation, reducing understory as length between fires and drought increases. Shrub establishment in the understory provides a zone of protection to allow seedling trees to establish further enabling the transition.

State 2
Pinyon-Juniper Invasive

This state occurs when there is an absence of natural disturbance (i.e. Insects, drought, or fire) over long time frames (Zlatnik, 1999). Also, management actions could have allowed trees to become very mature and have effectively removed understory. Invasive plants have increased in abundance. This state has the lowest resiliency and resistance. Seeding, with either natural disturbance or vegetation management to mimic the historic disturbance regime, may be necessary to transition to State 1 (Reference State). In some cases, there may be no practicable way back to reference, due to the large amounts of energy and monetary inputs that are needed.

Community 2.1
Pinyon-Juniper Woodland with Invasive Plants

A lack of understory with a canopy of older Pinyon and Juniper is the characteristics of this community phase. Interspaces of woody species and cover are very large and interconnected. This community phase occurs when natural or management actions allow for the increase in Pinyon and Utah juniper and a decrease in the grass and forb understory. Invasive or introduced plants species are present and are increasing.

Community 2.2
Invasive Annuals

This community phase is characterized by annual invasive grasses, like cheatgrass, dominating the understory. Other invasive species, like storkbill, may be present. This community phase has active erosion under the pinyon and Utah juniper canopy. Utah Juniper has allelopathic effects on some plants (i.e. Sandberg bluegrass) minimizing the native understory. Cheatgrass does not appear to be affected by this allelopathic effect when growing under juniper canopies (Zlatnik, 1999).

Pathway 2.1A
Community 2.1 to 2.2

Pinyon-Juniper Woodland with Invasive Plants

Invasive Annuals

This pathway occurs when events such as frequent fire (reduced fire return interval) or drought remove the trees and shrubs. Other factors in this pathway include be insect and pathogens outbreaks. Removal of canopy cover with reduced understory facilitates the establishment of cheatgrass or other invasive annuals. Cheatgrass will typically invade in the woody canopy interspaces when Pinyon-Juniper communities are degraded. Once the cheatgrass establishes, fine fuels increase exponentially in the community. The increase in fine fuels leads to shorter fire return interval inhibiting the recover and establishment of trees and shrubs. Cheatgrass and other invasive annuals can persist for long periods of time. The competitive nature of annuals alters the soil and other abiotic conditions of the community.

Pathway 2.2A
Community 2.2 to 2.1

Invasive Annuals

Pinyon-Juniper Woodland with Invasive Plants

This pathway occurs with a lack of fire and other disturbances. The use of firebreaks, invasive management, and fire suppression extend the fire return interval. Time without disturbance allows perennial grasses and woody species to establish with natural processes or may require further vegetation manipulation.

Transition T1A
State 1 to 2

This transition from the native perennial grass and shrub understory in the reference state to a state that has been invaded by naturalized species such as crested wheatgrass (blown in or seeded), cheatgrass, mustards, and other introduced or exotic plants. This transition occurs as natural and management actions favor an increase in non-native grasses and forbs, especially annuals. When this transition to State 2 occurs, the ecological site has lost much of its expected resistance and resilience. At this point natural and management actions have decreased the understory and erosion increases. Reduced influence from fire, insects, and drought could cause the tree canopy to close, effectively reducing the herbaceous understory, facilitating the transition. Improper grazing or increased surface disturbance combined with periods of drought can facilitate this transition because soil stability is lost and susceptibility to soil loss increases.

Constraints to recovery. Improper grazing or increased surface disturbance combined with periods of drought

Restoration pathway R2A
State 2 to 1

This transition is reducing tree canopy and re-establishment of grasses and forbs. This pathway may facilitate the recovery of the soils. The infrequent naturally occurring fires or other natural disturbances (insect/pathogen outbreak, wetter climatic cycles) could also cause this transition. Reseeding after a disturbance may be the only way to successfully restore the ecological dynamics to a site. Either way this pathway could involves large energy, time and monetary inputs by man.