Basalt Hills and Mesas 16-35 inches

Description

This state represents the most ecologically stable conditions in terms of resistance to erosion. Moreover, this state has the highest potential for productivity and plant diversity.

Reference State: This state reflects the pre-European conditions. Natural fires are a component of this state and generally occur with relatively moderate to high frequency, possibly averaging 25 to 40 years, and more frequently if fine fuels and climatic conditions allow for naturally ignited fires to expand. Crown fires are not expected to occur in this state due to the open nature of the stand of trees. No domestic livestock grazing is considered as part of this state. Understory vegetation is generally comprised of a mix of cool- and warm-season herbaceous vegetation, as well as a greater density and diversity of shrub species than in other states.

The reference state is dominated by old trees which comprise 75 to 90% of the stand, and mid-age trees comprise 15-20% or less. Trees less than 6 inches drc comprise 0-10% of the stand and may be virtually nonexistent in some isolated areas due to recurring low-intensity natural fires. Mature trees are long-lived and of large diameter, with few, if any, dead trees present, except for drought- and disease-affected trees.

Plant Community 1 (PC1): This is the climax plant community, self-sustaining through periodic natural fires with minimal susceptibility to insect damage or disease. This plant community is more commonly found on northerly aspects, dominated by pinyon with codominant or subdominant alligator juniper. Oneseed juniper is subdominant and held in check by frequent fires. Plant Community 2 (PC2) may result from significant pinyon mortality caused by severe drought, disease, and/or insects. This would allow alligator and oneseed junipers to surpass pinyon in density on north slopes. A juniper-dominated plant community is more commonly found on south slopes. Fire and drought would maintain a savannah plant community. Plant Community 3 (PC3) reflects an alligator juniper-dominated site where natural fire decreases the pinyon density, and likely decreases oneseed juniper density as well. Time, along with favorable moisture conditions, would allow pinyon to surpass alligator juniper and eventually lead to PC1. Alligator juniper provides a sheltered microclimate that aids in pinyon seedling establishment. Plant Community 4 (PC4) results from an overstory removal of all trees through a fuelwood harvest or mechanical means. Natural succession would move PC4 through either PC2 or PC3, eventually progressing to PC1 on north slopes. On south slopes, the PC4 plant community could revert back to and remain in PC2 or PC3.

In the reference state, tree density ranges between 40-50 trees/acre for the Alegros soil series and 50-60 trees/acre for the Smilo-Adman complex. Tree spacing is about 30-40 feet for pinyon and oneseed juniper and 50-60 feet for alligator juniper. Canopy cover ranges from 30-50%.

The canopy cover could vary among plant communities but is generally expected to be higher on north slopes and more open on south slopes.

The herbaceous component is comprised of a mixture of warm- and cool-season plants, such as sideoats grama, spike muhly, little bluestem, plains lovegrass, prairie junegrass, muttongrass, mountain muhly, littleseed ricegrass, sedges, and western wheatgrass. Gray oak is also found in the stands as a minor component in the overstory. Mountain mahogany and skunkbush sumac are found in the plant communities but in low quantities and in a healthy state.

Submodel

Description

State #2: This state has evolved as a result of long-term heavy grazing which has reduced the fine fuels necessary to maintain a natural fire regime. This state is represented by a deteriorated plant community typically occurring as Plant Community 5 (PC5), and is dominated by pinyon, codominant oneseed juniper, and subdominant alligator juniper. Natural fires (ground or crown) are essentially nonexistent. Tree densities are variable with higher densities occurring in small patches on the landscape. In PC5 a monoculture of blue grama exists along with invasive perennials or annuals. Very few shrub species are present, and usually found in decadent forms, as a result of grazing. Natural fire is not a component of the State #2 plant communities due to insufficient fine fuels or ladder fuels. Incidental fires may occur from individual tree lightning strikes and only burn in very small patches. State #2, typically has a site index class rating of “3” (0 to 50 basal area) prevailing, with lesser amounts of site index class 2 (51 to 100 basal area), and very few occurrences of site index class 1 (101 to 150 basal area) based on Howell’s site index method.

The State #2 characteristics are: a) tree densities are moderate to high, b) pinyon dominates most stands in frequency and canopy cover, c) landscapes are comprised of an uneven-aged stand of trees, d) pinyon seedling/sapling density exceeds that of junipers, e) herbaceous cover exhibits minimal plant diversity, density, and production, f) herbaceous cover is insufficient to protect the soil from wind and water erosion, and g) many communities contain dwarf mistletoe infestations and varying levels of pinyon mortality.

Overall in State #2, pinyon averages 67% of composition by frequency and 56% by canopy cover. Oneseed juniper is the dominant juniper species in frequency (17%) and canopy cover (24%). Alligator juniper dominates the old age-class, followed by oneseed juniper and then pinyon. Oneseed juniper and pinyon dominate the younger age-classes, indicating a potential for a future generation of a pinyon- and oneseed juniper-dominated stands. In general, pinyon is shorter-lived than the junipers with a mean age of 278 years (Swetnam and Brown, 1992). Pinyon trees are susceptible to adverse conditions (climate, disease infestations, soil productivity, and fire) that lead to mortality in the species at various ages, contributing to a shift in tree dominance. Conversely, alligator and oneseed junipers are long-lived and appear to be the mainstay in many of these woodland/savannah plant communities.

Incidental fires (single tree or small crown fires) caused by lightning strikes on individual trees may occur if fuel accumulations are sufficient at the base of the tree, such as from a packrat midden. Small area (patch-size) burns may occur if sufficient ground- and ladder-fuels are present, and if there are interlocking tree crowns along with extreme fire weather conditions (low humidity, high temperature, high wind velocity, and very low live-fuel moisture). These types of fires are typically rare and not likely to exceed 10 acres in size, due to the discontinuous fuel component and the variable stand densities.

Plant Community 6 (PC6) results as drought and disease reduces pinyon density in PC5. High mortality of pinyon would result in a plant community dominated by oneseed juniper on either north or south slopes. On north slopes, this plant community represents the developmental stage for the site to progress back to PC5. On some south slopes, this plant community may become static and persist. Plant Community 7 (PC7) would be a progressive plant community, whereas PC8 would shift over time to a plant community having pinyon as a codominant with oneseed juniper. PC7 is also a sequential plant community in the development from PC8 (Open grassland/shrub community) to PC5. This plant community can also be found on southerly aspects depending on the extent of pinyon mortality and pre-disturbance tree densities.

Plant Community 8 (PC8) would result from overstory removal of trees and result in an open grassland/shrub plant community with very little pinyon and juniper regeneration. Return to the HCPC would require tree regeneration through elimination of grazing and extensive land treatments such as thinning, reseeding, or fall burns.

Tree density ranges from 60-150 trees/acre and is generally dominated by pinyon with oneseed juniper secondary in dominance. Tree spacing averages about 15-25 feet for all species and age-classes combined. Canopy cover ranges from 35-65%. The canopy cover may be higher on north slopes than south slopes. The herbaceous component is dominated by blue grama with minor occurrences of spike muhly, squirreltail, prairie junegrass, littleseed ricegrass, and Fendler threeawn. Basal cover and forage production are very low. The shrub component is dominated by rubber rabbitbrush or spineless horsebrush with substantial densities of broom snakeweed. Desirable shrubs such as hairy mountain mahogany and gray oak are heavily browsed and decadent from overuse.

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Description

State #3: State #1 will transition to State #3 as a result of grazing (controlled and well managed), with modifications to the fire cycle. State #3 is comparable to State #1 although tree densities are higher in State #3, all age classes are represented, natural fire intervals become extended in terms of years (unless prescribed fire is used), herbaceous cover may vary more from State #1 (less composition and density), and shifts between tree species may be more pronounced.

Plant Community #9 (PC9) is the Potential Natural Community (PNC) dominated by pinyon and co-dominant with alligator juniper. This plant community is sustained through periodic fires, both natural and prescribed. Controlled grazing allows for fine fuels to accumulate and carry a fire through the plant community. In some instances, oneseed juniper may be co-dominant with alligator juniper on south slopes if fires become less frequent. Plant Community #10 (PC10) is a result of drought and disease reducing pinyon densities. The resulting plant community is dominated by alligator juniper (with a subdominant component of oneseed juniper and pinyon) and maintained by a frequent fire cycle. Plant Community #11 (PC11) results from overstory removal through fuelwood harvest or mechanical means. A shorter fire frequency would suppress oneseed juniper and allow alligator juniper to dominate the stands. Pinyon and oneseed juniper will increase in density over time, sequentially progressing toward PC10 and PC9.

The stand structure for State #3 is comparable to HCPC, although tree densities are less than 100 trees per acre for all species combined. Tree density ranges from 60-75 trees/acre for the Alegros soil series and 70-85 trees/acre for the Smilo-Adman complex depending on the fire cycle.

Tree density can be reduced with prescribed fire and mechanical land treatments such as mowing/mulching. Through land treatments, tree spacing and canopy cover may mimic HCPC levels. The herbaceous component is comprised of a mixture of warm- and cool-season plants, such as sideoats grama, spike muhly, little bluestem, plains lovegrass, prairie junegrass, muttongrass, mountain muhly, littleseed ricegrass, sedges, and western wheatgrass. Densities may vary depending on season of use by livestock and the extent of rest/deferment provided for plants to recover after grazing. Gray oak, hairy mountain mahogany, and skunkbush sumac occur in varying density and are represented by multiple age-classes and growth forms.

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Description

This data element was incorrectly entered as State 5. It has been retained in order to preserve production numbers.

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Description

This data element was incorrectly entered as State 6. It has been retained in order to preserve production numbers.

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