Ecological dynamics
The dominant visual aspect is basin big sagebrush with an understory of bluebunch wheatgrass. Composition by weight is approximately 60 to 70 percent grasses, 10 to 20 percent forbs, and 15 to 25 percent shrubs.
In the last few thousand years, this site has evolved in a semi-arid climate characterized by dry summers and cold winters. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, lagomorphs and small rodents.
Fire has historically occurred on the site at intervals of 20 to 50 years.
The Historic Climax Plant Community (HCPC), the Reference State (State 1), moves through many phases depending on the natural and man-made forces that impact the community over time. State 1, described later, indicates some of these phases. The Reference Plant Community Phase is Phase 1.1. This plant community is dominated by bluebunch wheatgrass in the understory and basin big sagebrush in the overstory. Subdominant species include Sandberg bluegrass, bottlebrush squirreltail,thickspike wheatgrass, arrowleaf balsamroot and tapertip hawksbeard. There is a large variety of other grasses, forbs and shrubs that can occur in minor amounts. The plant species composition of Phase 1.1 is listed later under “Reference Plant Community Phase Plant Species Composition”.
Total annual production is 600 pounds per acre (672 kilograms per hectare) in a normal year. Production in a favorable year is 1000 pounds per acre (1111 kilograms per hectare). Production in an unfavorable year is 400 pounds per acre (448 kilograms per hectare). Structurally, cool season deep rooted perennial bunchgrasses are very dominant, followed by tall shrubs being more dominant than perennial forbs while shallow rooted bunchgrasses are subdominant.
Function.
The Loamy 8-12 ARTRT/PSSPS site is suited for livestock grazing in the spring, early summer and fall. There are few limitations to grazing. The distance to water may be a problem in some areas. Usually this site is often the key area in a management program.
The site provides winter and spring range for mule deer. It has some value for sage grouse brood rearing.
The site has limited value for recreation but does provide some hunting, hiking, photography opportunities and off-road vehicle use.
Due to gentle slopes that allow easy access for livestock and relatively low production, this site can easily be degraded from improper livestock management. A mixed stand of shrubs and perennial grasses is necessary to reach the potential of the site.
Impacts on the Plant Community.
Influence of fire:
In the absence of normal fire frequency, basin big sagebrush can gradually increase on the site. Grasses and forbs decrease as shrubs increase. With the continued absence of fire, basin big sagebrush can displace most of the primary understory species.
When fire frequency is greater than historic levels, basin big sagebrush is reduced significantly. Rabbitbrush can increase slightly. With continued short fire frequency, basin big sagebrush can be completely eliminated along with many of the desirable understory species such as bluebunch wheatgrass, Nevada bluegrass, and needle and thread. These species may be replaced by Sandberg bluegrass and bulbous bluegrass along with a variety of annual and perennial forbs including noxious and invasive plants. Cheatgrass will invade the site. These fine fuels will increase the fire frequency.
Influence of improper grazing management:
Season-long grazing and/or excessive utilization can be detrimental to this site. This type of management leads to reduced vigor of the bunchgrasses. With reduced vigor, recruitment of these species declines. As these species decline, the plant community becomes susceptible to an increase in basin big sagebrush and noxious and invasive plants. Continued improper grazing management influences fire frequency by reducing fine fuels that carry fires. As cheatgrass increases and becomes co-dominant with Sandberg bluegrass and other annuals, fires become frequent.
A planned grazing system can be developed to intentionally accumulate fine fuels in anticipation of a prescribed fire. Brush management should be carefully planned, as a reduction in shrubs can increase cheatgrass leading to frequent fire intervals.
Weather influences:
Above normal precipitation in March, April and May can dramatically increase total annual production of the plant community. These weather patterns can also increase viable seed production of desirable species to provide for recruitment. Likewise, below normal precipitation during these spring months can significantly reduce total annual production and be detrimental to good seed production. Overall plant composition is normally not effected when perennials have good vigor.
Below normal temperatures in the spring can have an adverse impact on total production regardless of the precipitation. A hard, early freeze can kill some plants occasionally.
Prolonged drought adversely affects this plant community in several ways. Vigor, recruitment, and production are usually reduced. Mortality can occur. Prolonged drought can lead to changes in fire frequency.
Influence of Insects and disease:
Outbreaks can affect health of vegetation. Mormon cricket and grasshopper outbreaks occur periodically. Outbreaks seldom cause plant mortality since defoliation of the plant occurs only once during the year of the outbreak.
Influence of noxious and invasive weeds:
Annual and perennial invasive species compete with desirable plants for moisture and nutrients. The result is reduced production and change in composition of the understory. Cheatgrass can be very invasive on this site. Once it becomes established the fire frequency increases. As a result, the shrub component can be lost.
Influence of wildlife:
Big game use the Loamy 8-12 ARTRT/PSSPS site in the spring, summer and fall and in moderate winters. Their numbers are seldom high enough to adversely affect the plant community. Sage grouse may use the site for strutting grounds and also during the winter.
Watershed:
Decreased infiltration and increased runoff occur with an increase in basin big sagebrush. Desired understory species can be reduced. This composition change can affect nutrient and water cycles. Increased runoff also causes sheet and rill erosion. Abnormally short fire frequency also gives the same results, but to a lesser degree. The long term effect is a transition to a different state.
State 1
Reference State
The Reference State (State 1), the Historic Climax Plant Community (HCPC) moves through many phases depending on the natural and human forces that impact the community over time. The Reference Plant Community Phase is Phase 1.1, State 1. The plant species composition of Phase 1.1 is listed later under “Reference Plant Community Phase Plant Species Composition”.
Community 1.1
Basin big sagebrush/Bluebunch wheatgrass
The plant community in Community Phase 1.1 is dominated by bluebunch wheatgrass in the understory and basin big sagebrush in the overstory. Subdominant species include Sandberg bluegrass, bottlebrush squirreltail, thickspike wheatgrass, arrowleaf balsamroot, and tapertip hawksbeard. Natural fire frequency is 20 to 50 years.
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
260 |
455 |
650 |
| Shrub/Vine |
80 |
140 |
200 |
| Forb |
60 |
105 |
150 |
| Total |
400 |
700 |
1000 |
| 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
Basin big sagebrush
The plant community in Community Phase 1.2 is dominated by basin big sagebrush with reduced amounts of bluebunch wheatgrass and other deep rooted perennial grasses. Sandberg bluegrass and bottlebrush squirreltail have increased in the understory. All deep-rooted bunchgrasses are typically in low vigor. Basin big sagebrush has increased. Community Phase 1.2 has developed due to lack of disturbance, such as fire.
Community 1.3
Bluebunch wheatgrass/Sandberg bluegrass
The plant community in Community Phase 1.3 is dominated by bluebunch wheatgrass and Sandberg bluegrass. Bottlebrush squirreltail and thickspike wheatgrass have increased. Forbs remain about in the same proportion as Phase 1.1. Little basin big sagebrush is present due to wildfire, but some rabbitbrush and horsebrush are present due to sprouting. The plant community is the result of wildfire.
Pathway 1.1a
Community 1.1 to 1.2
Time since disturbance.
Pathway 1.1b
Community 1.1 to 1.3
Fire or other disturbance that removes shrubs.
Pathway 1.2a
Community 1.2 to 1.1
Disturbance to remove some shrub cover.
Pathway 1.3a
Community 1.3 to 1.1
Time since disturbance. This allows non-fire tolerant shrubs to establish in the community.
State 2
Current Potential
The Current Potential state is similar to the Reference State, with the addition of non-native species. Non-native species lower resistance and resilience to disturbance.
Community 2.1
Basin big sagebrush/bluebunch wheatgrass/non-native species
The plant community in Community Phase 1.2 is dominated by bluebunch wheatgrass in the understory and basin big sagebrush in the overstory. Subdominant species include Sandberg bluegrass, bottlebrush squirreltail, thickspike wheatgrass, arrowleaf balsamroot, and tapertip hawksbeard. Some cheatgrass may have invaded the site. Natural fire frequency is 20 to 50 years.
Community 2.2
Basin big sagebrush/non-native species
The plant community in Community Phase 2.2 is dominated by basin big sagebrush with reduced amounts of bluebunch wheatgrass and other deep rooted perennial grasses. Sandberg bluegrass and bottlebrush squirreltail have increased in the understory. All deep-rooted bunchgrasses are typically in low vigor. Basin big sagebrush has increased. Community Phase 2.2 has developed due to improper grazing management. Some cheatgrass may have invaded the site.
Community 2.3
Bluebunch wheatgrass/Sandberg bluegrass/Cheatgrass
The plant community in Community Phase 2.3 is dominated by bluebunch wheatgrass and Sandberg bluegrass. Bottlebrush squirreltail and thickspike wheatgrass have increased. Forbs remain about in the same proportion as Phase 2.1. Little basin big sagebrush is present due to wildfire, but some rabbitbrush and horsebrush are present due to sprouting. Some cheatgrass has invaded the site. Community Phase 2.4 is the result of wildfire.
Community 2.4
Sandberg bluegrass/non-native annual grasses
The plant community in Community Phase 2.4 is dominated by Sandberg bluegrass, cheatgrass, and other annuals. Root sprouting shrubs such as rabbitbrush and horsebrush can be present. Some soil loss has occurred. Community Phase 2.4 has developed due to frequent fires and improper grazing management.
Pathway 2.1a
Community 2.1 to 2.2
Time since disturbance, such as fire. Also can develop with season long grazing.
Pathway 2.1b
Community 2.1 to 2.3
Disturbance, such as fire, that reduces or eliminates sagebrush cover.
Pathway 2.2a
Community 2.2 to 2.1
Lack of disturbance to the understory grasses, such as reduction in grazing.
Pathway 2.3a
Community 2.3 to 2.1
Time since disturbance. Extended time since a disturbance, such as fire, allows the sagebrush to establish.
Pathway 2.3b
Community 2.3 to 2.4
Frequent disturbance, such as fire or grazing. The frequency of disturbance is outside of the normal or historical range.
State 3
Seeded State
The Seeded State has been seeded with non-native species that mimic the reference plant community.
Community 3.1
Seeded species
Community Phase 3.1 contains seeded species.
Transition T1A
State 1 to 2
Introduction and establishment of non-native species in the plant community. Annual non-native species, like cheatgrass, lower the site resistance and resilience to disturbance. This occurs through an increase in fine fuels that make the site more susceptible to fires. More frequent fires reduce shrub cover and increase non-native annual species. This positive feedback may lead to a transition to a different state that has not been identified (a potential State 4).
Transition T2A
State 2 to 3
Site is seeded with non-native perennial species.
