Ecological dynamics
These plant communities narratives do not represent every possibility, but they capture the most prevalent and repeatable plant communities. As data is collected, plant communities may be revised, removed, or new communities may be added. None of these plant communities should necessarily be thought of as “Desired Plant Communities”. According to the USDA NRCS National Range and Pasture Handbook, Desired Plant Communities (DPC’s) will be determined by the decision-makers and will meet minimum quality criteria established by the NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision.
Potential vegetation on the Dense Clay ecological site is dominated by drought resistant, mid-stature cool-season perennial grasses and shrubs. The expected potential composition for this site is 50% grasses, 10% forbs and 40% woody plants. The composition and production will vary naturally due to historical use and fluctuating precipitation.
As this site deteriorates, species such as Sandberg bluegrass and birdfoot sagebrush will increase. Plains pricklypear and weedy annuals will invade. Cool season grasses such as rhizomatous wheatgrass, bottlebrush squirreltail, and Indian ricegrass will decrease in frequency and production.
The reference Plant Community (description follows the plant community diagram) has been determined by study of rangeland relic areas, or areas protected from excessive disturbance. Trends in plant communities going from heavily grazed areas to lightly grazed areas, seasonal use pastures, and historical accounts have also been used.
The following is a State and Transition Model Diagram that illustrates the common plant communities (states) that can occur on the site and the transitions between these communities. The ecological processes will be discussed in more detail in the plant community narratives following the diagram.
State 1
Rhizomatous Wheatgrasses/Birdfoot Sagebrush
Figure 7. During a drought, the tolerant perennial grasses persist with birdfoot sagebrush.
The Dense Clay ecological site is generally small on the landscape, but is also very distinct with the low vegetative profile. This birdfoot sagebrush dominated site is prominently displayed in a patchwork with Wyoming big sagebrush of neighboring ecological sites. The herbaceous cover consists of a mixture of mid-stature and short-stature cool-season bunchgrasses and rhizomatous grasses.
Characteristics and indicators. A diverse mixture of key perennial grasses, forbs and the dominant birdfoot sagebrush is the key characteristic of this State.
Resilience management. The vegetation of this State are resilient to drought and use, and tend to be resistant to degradation. However, with long-term or repeated pressures, this community will shift.
Community 1.1
Rhizomatous Wheatgrasses/Birdfoot Sagebrush
The interpretive plant community for this site is the Reference State. This state evolved with grazing by large herbivores and very droughty soils due to the very slow infiltration rate. Potential vegetation is dominated by salt tolerant, drought resistant, mid cool-season perennial grasses and shrubs. The expected potential composition for this site is about 50 percent grasses, 10 percent forbs and 40 percent woody plants.
The major grasses include rhizomatous wheatgrasses, bottlebrush squirreltail, and Indian ricegrass. A variety of forbs and half-shrubs also occur, as shown in the preceding table. Birdfoot sagebrush and Gardner saltbush comprise almost half of the total annual production. Winterfat is a common component found on this site. A variety of forbs also occurs in this state and plant diversity is high (see Plant Composition Table).
The total annual production (air-dry weight) of this state is about 300 pounds per acre, but it can range from about 150 lbs/acre in unfavorable years to about 450 lbs./acre in above average years.
Resilience management. This state is extremely stable and well adapted to the climatic conditions within the foothills and basin. The diversity in plant species allows for high drought resistance. This is a sustainable plant community (site/soil stability, watershed function, and biologic integrity).
Dominant resource concerns
-
Wind erosion
-
Compaction
-
Sediment transported to surface water
-
Terrestrial habitat for wildlife and invertebrates
-
Inadequate livestock shelter
-
Inadequate livestock water quantity, quality, and distribution
Table 5. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Grass/Grasslike |
106 |
196 |
280 |
| Shrub/Vine |
56 |
112 |
168 |
| Forb |
6 |
28 |
56 |
| Total |
168 |
336 |
504 |
Table 6. Soil surface cover
| Tree basal cover |
0%
|
| Shrub/vine/liana basal cover |
0-10%
|
| Grass/grasslike basal cover |
0-5%
|
| Forb basal cover |
0-5%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0-5%
|
| Litter |
5-15%
|
| Surface fragments >0.25" and <=3" |
0-10%
|
| Surface fragments >3" |
0-5%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
30-60%
|
Table 7. Canopy structure (% cover)
| Height Above Ground (m) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.15 |
– |
10-25% |
5-15% |
1-5% |
| >0.15 <= 0.3 |
– |
0-15% |
0-15% |
0-5% |
| >0.3 <= 0.6 |
– |
– |
0-5% |
– |
| >0.6 <= 1.4 |
– |
– |
– |
– |
| >1.4 <= 4 |
– |
– |
– |
– |
| >4 <= 12 |
– |
– |
– |
– |
| >12 <= 24 |
– |
– |
– |
– |
| >24 <= 37 |
– |
– |
– |
– |
| >37 |
– |
– |
– |
– |
| Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
Community 1.2
Mixed Perennial Grass/Birdfoot Sagebrush
This plant community is the result of moderate continuous season long grazing and is exacerbated by prolong drought conditions. Birdfoot sagebrush composes a significant percentage of the annual production of plant community. Cool-season grasses make up the majority of the understory with the balance made up of short warm season grasses, and miscellaneous forbs.
Dominant grasses include rhizomatous wheatgrasses, and bottlebrush squirreltail and Sandberg bluegrass. Forbs commonly found in this plant community include wild onion, scarlet globemallow, fringed sagewort, smooth woody aster, wild parsley, and phlox. Birdfoot Sagebrush can make up to 50% of the annual production. Plains pricklypear cactus can also occur.
When compared to the Reference Community Phase, birdfoot sagebrush has increased. Production of cool-season grasses, particularly Indian ricegrass, has been reduced, as have shrubs such as winterfat. This diverse plant community provides support for domestic livestock and wildlife such as antelope.
The total annual production (air-dry weight) of this state is about 200 pounds per acre, but it can range from about 75 lbs./acre in unfavorable years to about 300 lbs./acre in above average years.
Resilience management. This plant community is resistant to change. The herbaceous species present are well adapted to grazing; however, species composition can be altered through long-term overgrazing. The herbaceous component is mostly intact and plant vigor and replacement capabilities are sufficient. Water flow patterns and litter movement may be occurring but only on steeper slopes. Incidence of pedestalling is minimal. Soils are mostly stable and the surface shows minimum soil loss. The watershed is functioning and the biotic community is intact.
Dominant resource concerns
-
Sheet and rill erosion
-
Wind erosion
-
Compaction
-
Sediment transported to surface water
-
Terrestrial habitat for wildlife and invertebrates
-
Feed and forage imbalance
-
Inadequate livestock shelter
-
Inadequate livestock water quantity, quality, and distribution
Pathway CP1.1-1.2
Community 1.1 to 1.2
This plant community is the result of moderate continuous season long grazing and is exacerbated by prolong drought conditions. Time and timing of grazing may also have an effect on this transition or may help reduce the risk of this transition.
Pathway CP1.2-1.1
Community 1.2 to 1.1
Long-term Prescribed Grazing – With extended grazing management, allowing rest and rotation, these sites may be prevented from further degradation, and will see a return to a reference state composition over very extended periods.
| Critical Area Planting |
|
| Prescribed Grazing |
|
State 2
Birdfoot Sagebrush/Bare Ground
The harsh environment presented by the soils of the Dense Clay ecological site limit the persistence of most perennial grasses. Although, the species that are key to this site are resilient species, after long term pressure, the community will shift to a birdfoot sagebrush only community.
Characteristics and indicators. The lack of herbaceous vegetation within the birdfoot sagebrush canopy is the key indication of being in this community. A few annual forbs may occur and a few perennial forbs, but most grasses are not present.
Resilience management. Once this community has established recruitment of key grasses is difficult making this community resilient and resistant to change.
Community 2.1
Birdfoot Sagebrush/Bare Ground
This plant community is the result of frequent and severe grazing and is exacerbated by prolonged periods of drought. Birdfoot sagebrush dominates this plant community, as the annual production is in excess of 50 percent. The preferred cool season grasses have been eliminated or greatly reduced.
The dominant grass is Sandberg bluegrass, or mutton bluegrass at a slightly higher elevation. Weedy annual species such as cheatgrass, halogeton, and Russian thistle will occupy the site if a seed source is available. Cactus has increased. Plant diversity is poor. The interspaces between plants have expanded significantly leaving mostly bare ground. When compared to the historic climax plant community the perennial cool-season grasses are absent and birdfoot sage and annuals dominate.
The total annual production (air-dry weight) of this state is about 125 pounds per acre, but it can range from about 50 lbs/acre in unfavorable years to about 200 lbs./acre in above average years.
Resilience management. This plant community is resistant to change as the stand becomes more decadent. Continued frequent and severe grazing or the removal of grazing does not seem to affect the plant composition or structure of the plant community. Plant diversity is greatly altered and the herbaceous component is not intact. Recruitment of perennial grasses is not occurring and the replacement potential is absent. The biotic integrity is missing.
Soil erosion is accelerated because of increased bare ground. Water flow patterns and pedestalling are obvious. Infiltration is reduced and runoff is increased. Rill channels are noticeable in the interspaces and gullies are being establishing where rills have concentrated down slope. The watershed may or may not be functional.
State 3
Invaded
Figure 10. A healed dozer trail carries a prominent cover of curlycup gumweed and an unexpected cover of fringed sagewort suggesting alteration of the soil characteristics for this site.
This state, the Invaded State, is less consipicuous than neighboring ecological sites. Cheatgrass and other invasive species will establish in this community, but do not tend to become extensive.
Characteristics and indicators. The significant presence of an invader species, of at least 5 percent by cover, qualifies a State as being invaded.
Resilience management. As annuals or other invasive species increase the native grasses are weakened and eventually removed from the community. The resulting invader/saltbush dominated community is resistant and resilient against change. Cheatgrass may be a common threat, but unlike big sagebrush communities, birdsfoot sagebrush is able to maintain and prevent the dense monoculture stands of Cheatgrass. The corresponding fire risk of cheatgrass continues to be muted by the reduced fine fuels.
Community 3.1
Invaded
The major invasive species that are moving into the Big Horn Basin and lower foothill regions are: cheatgrass, Russian Knapweed, whitetop, and a variety of thistles. Cheatgrass is the major threat to the foothills. The potential risk of becoming a monoculture of cheatgrass has been minimal on the Dense Clay ecological site due to the low herbaceous potential pre-disturbance. Many of these areas are used frequently by recreationalists for 4-wheeling, shooting, etc due to the open barren nature. With the increased “traffic” and corresponding increase in soil disturbance provides for a more prevalent and abundant seed source as well as improved seedling establishment created by the loosening of the soil surface.
Resilience management. This plant community is resistant to change as the stand becomes more decadent. Continued frequent and severe grazing, or the removal of grazing, does not seem to affect the plant composition or structure of this plant community. Plant diversity is greatly altered and the herbaceous component is not intact. Recruitment of perennial grasses is not occurring and the replacement potential is minimal. The biotic integrity is missing.
State 4
Altered
This state is a dynamic state to capture those communities that have been disturbed or altered due to alternative uses including recreation, farming, energy development and other general land uses with soil surface disturbances.
Characteristics and indicators. The visual signs of disturbance or manipulation of the soil or the presence of seeded species are the key indications of an altered landscape.
Resilience management. Climatic conditions and soil limitations restrict the feasibility of manipulating the native vegetation or degraded sites with much success. Additional inputs to help improve soil quality as well as artificial watering systems to assist in seedling establishment have been costly, and troublesome. Irrigating/watering these sites has created issues with surface crusting, inhibiting seedling emergence. Intensity and timing of natural precipitation has proved risky and nearly impossible to achieve a high level of success. However, areas have had acceptable establishment with introduced or improved plant varieties. Large landscapes of this ecological concept have been identified surrounding or intermixed with active bentonite mines, oil/gas developments, or have been used for recreational vehicles. The level and extent of disturbance varies greatly between uses. These are all factors considered in the following Community description.
Community 4.1
Disturbed
This ecological site is generally small in size on the landscape, and is intermixed with other productive sites. So many times, these areas are used for parking vehicles or are incidental in many other land alteration practices, and are not a focus for management. Increased vehicle or motorized traffic, reacreational uses, and lounging areas for livestock and wildlife can significantly impact these areas. The barren tendancy/nature of this ecological site provides an easy location for a salt lick or mineral tub. As this increased pressure impacts the vegetation shifts to an annual driven community, until time or rest is provided to allow natural succession to occur or reclamation of the site occurs. Natural succession is slow, and limited by the droughty nature of the soils. Seeding is also difficult, but has proven more successful with higher precipitation.
Resilience management. Climatic conditions and soil limitations restrict the feasibility of manipulating the native vegetation or degraded sites with much success. Additional inputs to help improve soil quality as well as artificial watering systems to assist in seedling establishment have been costly, and troublesome. Irrigating/watering these sites has created issues with surface crusting, inhibiting seedling emergence. Intensity and timing of natural precipitation is limiting, but has had greater success than at lower elevations. Areas have had acceptable establishment with introduced or improved plant varieties.
Dominant resource concerns
-
Sheet and rill erosion
-
Classic gully erosion
-
Compaction
-
Sediment transported to surface water
-
Plant productivity and health
-
Plant structure and composition
-
Plant pest pressure
-
Terrestrial habitat for wildlife and invertebrates
-
Feed and forage imbalance
-
Inadequate livestock shelter
-
Inadequate livestock water quantity, quality, and distribution
Transition T1-2
State 1 to 2
Frequent and severe grazing, will convert the plant community to the Birdfoot Sagebrush/Bare Ground Community Phase. The probability of this occurring is high on areas where birdfoot sagebrush is not adversely impacted by heavy browsing and prolong drought has occurred.
Constraints to recovery. The ability for native grasses to establish in this tough soil.
Transition T1-3
State 1 to 3
Rhizomatous Wheatgrasses/Birdfoot Sagebrush
Drought, Disturbance or Over-use with Seed Source present - When drought or a disturbance such as over-use by grazers occurs the vulnerability of the state is opened and when there is a seed source present, invasive species can gain a foot hold quickly due to the open canopy and low plant density.
Constraints to recovery. Recovery is limited to the ability to control or eradicate the species of invasion.
Restoration pathway R2-1
State 2 to 1
Prescribed grazing or possibly long-term prescribed grazing, will convert this plant community to the Reference State. The probability of this occurring is high especially if rotational grazing along with short deferred grazing is implemented as part of prescribed method of use. Brush management is not usually necessary at the time these grazing systems are implemented.
Context dependence. The seed bank or nursery stock is needed to aid the recovery process in the system.
| Critical Area Planting |
|
| Prescribed Grazing |
|
Transition T2-3
State 2 to 3
Continued Disturbance or Lack of Use/Management with Seed Source present - Repeated extensive use by recreational traffic is common on the raw or "disturbed" appearance of reclaimed or manipulated areas. These at-risk locations are vulnerable to weed encroachment, especially by aggressive invasive species that are persistent within the Big Horn Basin and lower foothills. Cheatgrass has seed sources readily available and easily transported on tires, undercarriages, animals, and humans. With continued presence of activity or movement through disturbed or establishing communities, the risk of transitioning to an invaded state increases.
Constraints to recovery. The ability to control the invasive species is the major constraint to recovery for this community.
Restoration pathway R3-4
State 3 to 4
Grazing management after the use of seedings following soil amendments or other techniques to aid establishment of native or improved varieties and an intense weed management plan will aid the recovery of this community.
| Critical Area Planting |
|
| Prescribed Grazing |
|
| Grazing Land Mechanical Treatment |
|
| Heavy Use Area Protection |
|
| Recreation Area Improvement |
|
| Integrated Pest Management (IPM) |
|
Transition T4-3
State 4 to 3
Drought, Disturbance or Over-use with Seed Source present - When drought or a disturbance such as over-use by grazers occurs the vulnerability of the state is opened and when there is a seed source present, invasive species can gain a foot hold quickly due to the open canopy and low plant density.
Constraints to recovery. Recovery is limited to the ability to control or eradicate the species of invasion.
