Ecological dynamics
The Droughty Steep (DrStp) ecological site is characterized by the production and composition of the Reference Plant Community, which is defined by soils, precipitation, and the temperature regime influencing the site. In the Beaverhead Mountains LRU of MLRA 43B, Subset D has a Typic, Ustic soil moisture regime and Cryic temperature regime. This equates to 15 to 19 inches of relative effective annual precipitation and between 50 and 70 consecutive frost-free days. The Droughty Steep ecological site is characterized by having skeletal soils greater than 20 inches deep and by not being strongly or violently effervescent in the top 4 inches of the soil surface and having slopes greater than 15 percent. This is an upland site that is heavily influenced by aspect and variations in plant communities do exist as a result.
The majority of precipitation comes in late April to late June. Primary growth typically occurs between May and July with dominant plants that have adapted to these conditions. The warmer, drier section of this LRU primary growth typically occurs between April and June. A period of fall green-up can occur amongst this cool-season dominated plant community if adequate precipitation is present.
The reference plant community is dominated by bluebunch wheatgrass (Pseudoroegneria spicata), and Idaho fescue (Festuca idahoensis). Subdominant species include Wyoming and mountain big sagebrush with thickspike wheatgrass (Elymus lanceolatus), Columbia needlegrass (Achnatherum nelsonii), needle and thread (Hesperostipa comata), and green needlegrass (Nassella viridula). The Soil and Vegetation Inventory of Near-pristine Sites of Montana suggests that the reference community is dominated primarily of bunchgrasses with approximately 20 percent of the community being shrubs (Ross et al. 1973). Other historical accounts also suggest that sagebrush and shrubs were less extensive as part of the historic plant community for this area (Hayden 1873).
As stated above both Wyoming big sagebrush (Artemisia tridentata ssp wyomingensis) and mountain big sagebrush (Artemisia tridentata spp vasayena) exist on this site; sometimes in a homogeneous nature. This overlap of subspecies may express a third genotype of big sagebrush known as Bonneville big sagebrush (Artemisia tridentata ssp xbonnevillensis). This hybridization of Wyoming and mountain big sagebrush has not been officially observed in this LRU, however it does occur on similar landscapes, with similar climates, in Western Wyoming, Eastern Idaho, and Northeast Utah .
Fire has historically been a powerful driver of this community. Some estimates of fire return may have been as long as 200 years in some sagebrush communities, however a local study (Arno and Gruell 1982) suggests a fire return interval of 20 to 40 years. These frequent fires limited conifer expansion on this site, maintained potential for small aspen groves, and limited dense sagebrush communities. Communities that have changed over time to be dominated by three-tip sagebrush (Artemisia tripartita) may be a result of frequent fire that removed or suppressed big sagebrush.
The Droughty Steep Ecological Site occurs across a relatively large landscape with slight variations within the plant community occurring due to elevation, frost-free days, aspect, and relative effective annual precipitation. These slight variations tend to manipulate the amounts of individual species, however the core species community is rarely changed. For example all variations of this site will express bluebunch wheatgrass, however drier sites will have an increased amount of Sandberg bluegrass and needle and thread while wetter sites will express an increase of Columbia needlegrass and green needlegrass.
The Droughty Steep ecological site is largely intact and being primarily used for livestock grazing. Historical records indicate, prior to the introduction of livestock (cattle and sheep) during the late 1800’s, elk and bison grazed this ecological site (Lesica and Cooper 1997). Due to the nomadic nature and herd structure of bison, areas that were grazed received periodic high intensity short duration grazing pressure. Meriwether Lewis documented that he was met by 60 Shoshone warriors on horseback in August 1805 and the Corps of Discovery was later supplied with horses by the same band of Shoshone (Moulton and Dunlay 1988). This suggests that the areas near the modern day towns of Twin Bridges, Bannack, Dillon, Grant, Dell, Tendoy, Leadore, and Salmon were grazed by an untold number of horses for years prior to the large introduction of cattle and sheep.
Livestock grazing has occurred on most of this ecological site for more than 150 years. The gold boom in the 1860s brought the first herds of livestock overland from Texas, and homesteaders began settling the area. Since the 1930s, cattle production has dominated the livestock industry in the region (Wyckoff and Hansen 2001).
Dense clubmoss (Selaginella densa), in general, is a very minor component of Reference plant community of the Droughty Steep ecological site. The conditions that created large cover classes of clubmoss on this site point to a history of continuous (yearlong) or moderate spring grazing use (Sturm 1954). While dense clubmoss provides soil stability on the sites it exists, anecdotal accounts by some land managers suggest that it competes for the limited water resources in the upper soil profile which, in turn, restricts plant available water. However, a study from Canada (Colberg and Romo 2003) in a similar climate and on similar soils indicates that the correlation between reduced plant available water and clubmoss cover is negligible. The correlation between reduced plant production may simply be competition for space though quantitative evidence is unavailable. Dense patches of clubmoss also inhibit seed contact with soil reducing seedling recruitment.
Some of the major invasive species that can occur on this site include (but not limited to) spotted knapweed (Centaurea stoebe), leafy spurge (Euphorbia esula), cheatgrass (Bromus tectorum), field brome (Bromus arevensis), yellow toadflax (Linaria vulgaris), Kentucky bluegrass (Poa pratensis), and dandelion (Taraxicum spp). Invasive weeds are beginning to have a high impact on this ecological site due to primarily human impacts, mismanaged grazing, and urban development. Cheatgrass and spotted knapweed pose the largest threat to this ecological site.
Plant Communities and Transitional Pathways
A State and Transition Model for the Droughty Steep Ecological Site is depicted below. Thorough descriptions of each state, transition, plant community, and pathway follow the model. This model is based on available experimental research, field data, field observations, and interpretations by experts. It is likely to change as knowledge increases.
The plant communities within the same ecological site will differ across the MLRA due to the naturally occurring variability in weather, soils, and aspect. The biological processes on this site are complex; therefore, representative values are presented in a land management context. The species lists are representative and are not botanical descriptions of all species occurring, or potentially occurring, on this site. They are intended to cover the core species and known range of conditions and responses.
Both percent species composition by weight and percent canopy cover are referenced in this document. Most observers find it easier to visualize or estimate percent canopy for woody species (trees and shrubs). Canopy cover drives the transitions between communities and states because of the influence of shade, interception of rainfall and competition for available water. Species composition by dry weight remains an important descriptor of the herbaceous community and of the community as a whole. Woody species are included in species composition for the site. Calculating similarity index requires use of species composition by dry weight.
This State and Transition Model (STM) includes only rangeland communities and states. The converted communities are described in the Ecological Dynamics of the Site section above.
Although there is considerable qualitative experience supporting the pathways and transitions within the State and Transition Model (STM), no quantitative information exists that specifically identifies threshold parameters between grassland types and invaded types in this ecological site. For information on STMs, see the following citations: Bestelmeyer et al. 2003; Bestelmeyer and Brown 2005a; Bestelmeyer and Brown 2005b; Briske et al. 2008; Bestelmeyer et al. 2010; Bestelmeyer et al. 2016
State 1
Reference State
Figure 9. Droughty Steep Reference Community
The Reference State of this ecological site consists of two known potential plant communities, Bluebunch Community (1.1) and Mixed Bunchgrass Community (1.1). These are described below but are generally characterized by a mid-statured, cool-season grass community with limited shrub production. Community 1.1 is dominated by bluebunch wheatgrass with subdominants of Idaho fescue, green needlegrass, and thickspike wheatgrass. This community is considered the Reference Plant Community while Community 1.2 is an At-Risk Plant Community for this state; co-dominated by bluebunch wheatgrass and Idaho fescue with big sagebrush as the dominant shrub.
Community 1.1
Bluebunch Community
In the Bluebunch Community(1.1), bluebunch wheatgrass (Pseudoroegneria spicata), Idaho fescue (Festuca idahoensis), and Columbia needlegrass (Acnatherum nelsonii) are dominant. Basin wildrye (Elymus cinerus), green needlegrass (Nasella viridula), and Sandberg bluegrass (Poa sandbergii) will be subordinate grasses. Shrub species such as common snowberry (Symphoricarpus albus), mountain big sagebrush (Artemisia tridentata ssp vaseyana), Wyoming big sagebrush (Artemisia tridentata ssp wyomingensis), and spineless horsebrush (Tetradymia canescence) remain a minor part of the community (Hayden 1873). In areas where the soil texture is coarser, spineless horsebrush (Tetradymia canescens) tends to be more common. Cusick's bluegrass (Poa cusickii) and dryland sedges will also be present.
This community occurs in areas with low grazing use. Prior to the introduction of expansive livestock herds, basin wildrye may have dominanted this ecological site as suggested by a Forest Service Technical Report (Gruell 1983), however quantitative evidence is lacking as relict sites a very few and small in size.
Bluebunch wheatgrass lacks resistance to grazing during the critical growing season and will decline in vigor and production if grazed in the critical growing season more than one year in three (Wilson et al. 1960). The critical growing period for bluebunch wheatgrass is late spring (June). This community is moderately resilient and will return to dynamic equilibrium following a relatively short period of stress (such as drought or short-term improper grazing), provided a return of favorable or normal growing conditions, and properly managed grazing. Improper grazing is defined as grazing utilization that exceeds moderate use (less than 50 percent grazing use) or multiple grazing events of a plant in the same growing season without rest.
As discussed in the Ecological Dynamics Section, natural fire regime restricted shrubs to relatively small portions of Community 1.1. Shrub species not listed above may also include, but not limited to, Bonneville big sagebrush (Artemisia tridentata ssp xbonnevillensis), mountain snowberry (Symphoricarpos oreophilus), shrubby cinquefoil (Dasiphora fruiticosa), winterfat (Krascheninnikovia lanata), tarragon (Artemisia drucunculus), and fringed sagewort (Artemisia frigida).
Dominant plant species
-
mountain big sagebrush (Artemisia tridentata ssp. vaseyana), shrub
-
common snowberry (Symphoricarpos albus), shrub
-
Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), shrub
-
spineless horsebrush (Tetradymia canescens), shrub
-
yellow rabbitbrush (Chrysothamnus viscidiflorus), shrub
-
bluebunch wheatgrass (Pseudoroegneria spicata), grass
-
Idaho fescue (Festuca idahoensis), grass
-
basin wildrye (Leymus cinereus), grass
-
western wheatgrass (Pascopyrum smithii), grass
-
lupine (Lupinus), other herbaceous
-
common yarrow (Achillea millefolium), other herbaceous
-
beardtongue (Penstemon), other herbaceous
-
western stoneseed (Lithospermum ruderale), other herbaceous
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
630 |
825 |
1050 |
| Shrub/Vine |
180 |
205 |
250 |
| Forb |
90 |
120 |
150 |
| Tree |
0 |
10 |
50 |
| Total |
900 |
1160 |
1500 |
Table 6. Ground cover
| Tree foliar cover |
0-1%
|
| Shrub/vine/liana foliar cover |
5-20%
|
| Grass/grasslike foliar cover |
25-40%
|
| Forb foliar cover |
5-12%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0-3%
|
| Litter |
20-35%
|
| Surface fragments >0.25" and <=3" |
5-20%
|
| Surface fragments >3" |
0-15%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0%
|
Table 7. Soil surface cover
| Tree basal cover |
0%
|
| Shrub/vine/liana basal cover |
1-5%
|
| Grass/grasslike basal cover |
5-10%
|
| Forb basal cover |
1-3%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0-3%
|
| Litter |
20-35%
|
| Surface fragments >0.25" and <=3" |
5-20%
|
| Surface fragments >3" |
0-15%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0-15%
|
Community 1.2
Mixed Bunchgrass Community
Idaho fescue and bluebunch wheatgrass share dominance in the Mixed Bunchgrass Community (1.2). Other grass species, which are more tolerant to grazing and are likely to increase compared to the Bluebunch Community, include Sandberg bluegrass (Poa secunda), Cusick's bluebrass (Poa cusickii), prairie Junegrass (Koeleria macrathana), western/thickspike wheatgrass (Pascopyrum smithii, Elymus lanceolatus), and needle and thread (Hesperostipa comata). Some increaser forbs species include western yarrow (Achillea millefolium), Hoods phlox (Phlox hoodii), scarlet globemallow (Sphaeralcea coccinea), hairy goldenaster (Heterotheca villosa), prairie smoke (Geum triflorum), and pussytoes (Antennaria spp.). Fringed sagewort may also increase under prolonged drought or heavy grazing and can respond to precipitation that falls in July and August.
Idaho fescue tolerates grazing pressure better than bluebunch wheatgrass and Columbia needlegrass. The growing point for bluebunch wheatgrass is several inches above the ground, making them very susceptible to continued close grazing (Smoliack, et al 2006), while Idaho fescue's growing point tend to be near the plant base. These grasses increase in species composition when more palatable and less grazing tolerant plants decrease due to overgrazing, drought, or intense fire.
Heavy, continuous grazing will reduce plant cover, litter, and soil organic matter. Timing of grazing is important on this site as grazing bluebunch wheatgrass in summer season has proven to negatively impact seasonal regeneration, especially on the drier sites. Bare ground will increase which may increase soil erosion. Litter and mulch will be reduced as plant cover declines. As long as bluebunch wheatgrass is still a dominant species of total biomass production, the site can return to the Bluebunch Community (Pathway 1.2A) under proper grazing management and favorable growing conditions. In this community, proper grazing management is a grazing rotation that favors bluebunch wheatgrass. This grazing management plan would include conservative grazing use with light to moderate grazing use during the critical growing season which is early to mid summer (boot stage of the plant) or preferably dormant grazing use. (Wilson et al. 1966; McLean and Wikeem 1985)
Over time, Idaho fescue, needle and thread, and western wheatgrass will increase until they make up the majority of species composition. Once bluebunch wheatgrass has been reduced to less than 20 percent by dry weight it may be difficult for the site to recover to Bluebunch Community (1.1). The risk of soil erosion increases when canopy cover decreases. As soil conditions degrade, there will be loss of organic matter, reduced litter, and reduced soil fertility. Degraded soil conditions increase the difficulty of reestablishing bluebunch wheatgrass preventing the return to the Bluebunch Community (1.1).
The Mixed Bunchgrass Community (1.2) is considered the At-Risk Plant Community for this ecological site. When overgrazing continues increaser species such as needle and thread and native forb species will become more dominate and this triggers the change to the Altered State (2) or the Degraded State (3). Until the Mixed Bunchgrass Community (1.2) crosses the threshold into the Mixed Sagebrush Community (2.1) or the Invaded Community (4.1), this community can be managed toward the Bluebunch Community (1.1) using prescribed grazing and strategic weed control. It may take several years to achieve this recovery, depending on growing conditions, vigor of bluebunch and other midstatured bunchgrass plants, and the aggressiveness of the weed treatments (if necessary).
Dominant plant species
-
big sagebrush (Artemisia tridentata), shrub
-
common snowberry (Symphoricarpos albus), shrub
-
rubber rabbitbrush (Ericameria nauseosa), shrub
-
spineless horsebrush (Tetradymia canescens), shrub
-
bluebunch wheatgrass (Pseudoroegneria spicata), grass
-
Idaho fescue (Festuca idahoensis), grass
-
fleabane (Erigeron), other herbaceous
-
American vetch (Vicia americana), other herbaceous
-
phacelia (Phacelia), other herbaceous
-
twinpod (Physaria), other herbaceous
-
lupine (Lupinus), other herbaceous
-
stonecrop (Sedum), other herbaceous
Pathway 1.1A
Community 1.1 to 1.2
Mid-statured bunchgrasses lose vigor with improper grazing (see definition below), extended drought, or unusually hot fire. When vigor declines in response to disturbances such as these, bunchgrass basal areas will decrease in size while species with higher grazing tolerance (primarily Idaho fescue on this site) increase in vigor and production as they access the resources previously used by bluebunch wheatgrass. The decrease of bluebunch wheatgrass to less than 30 percent composition indicates that the plant community has shifted to the Mixed Bunchgrass Community (1.2). The driver for community shift 1.1A is improper grazing management or prolonged drought. This shift is triggered by the loss of vigor of bluebunch wheatgrass, soil erosion, or prolonged drought coupled with improper grazing. Blaisdell (1958) stated that drought and warmer than normal temperatures are known to advance plant phenology by as much as one month. During drought years, plants may be especially sensitive or in a critical stage of development earlier than expected.
Improper grazing on this ecological site is defined as grazing utilization that exceeds moderate use (less than 50 percent grazing use) and/or multiple grazing events of a plant in the same growing season without rest. Associated with grazing intensity is timing of grazing. Bluebunch wheatgrass's critical grazing period is late spring.
Pathway 1.2A
Community 1.2 to 1.1
The Mixed Bunchgrass Community (1.2) will return to the Bluebunch Community (1.1) with proper grazing management and appropriate grazing intensity. Favorable moisture conditions will facilitate or accelerate this transition. It may take several years of favorable conditions for the community to transition back to a bluebunch dominated state. The driver for this community shift (1.2A) is increased vigor of bluebunch wheatgrass to the point that it represents more than 20 percent of species composition. The trigger for this shift is the change in grazing management favoring bluebunch wheatgrass. In general, conservative grazing management styles such as deferred or rest rotations utilizing moderate grazing (less than 50 percent grazing use) coupled with favorable growing conditions like cool, wet springs are these triggers. These systems tend to promote increases in soil organic matter which, in turn, also promotes microfauna and increased infiltration rates. Inversely, long periods of rest at a time when this state is considered to be stable may not result in an increase in bluebunch wheatgrass. It has been suggested (Noy-Meir 1975) that these long periods of rest or underutilization may actually drive the system to a lower level of stability by creating large amounts of standing biomass, dead plant caudex centers, and gaps in the plant canopy.
| Prescribed Burning |
|
| Prescribed Grazing |
|
State 2
Altered State
This state is characterized by having less than 15 percent bluebunch wheatgrass by dry weight. It is represented by two communities that differ in the percent composition of Idaho fescue and needle and thread, overall production, and soil degradation. Production in this state can be similar to the Reference State (1). Some native plants tend to increase under prolonged drought and heavy grazing practices. A few of these species may include Idaho fescue, needle and thread, Sandberg bluegrass, Cusick's bluegrass, scarlet globemallow, hairy goldenaster, and fringed sagewort. Poisonous plants such as lupine (Lupinus spp) and mountain deathcamas (Zigadenus elegans) may also increase under these conditions.
Community 2.1
Mixed Sagebrush Community
Needle and thread and Idaho fescue dominate this Mixed Sagebrush Community (2.1). Bluebunch wheatgrass comprises up to 15 percent of species composition by dry weight and the remaining mid-statured bunchgrasses tend to be scattered and low in vigor. Increaser and invader species will be more common. Increaser forb species include hairy goldenaster, Missouri goldenrod, stonecrop, lupine, and yarrow. It is not uncommon for a minor component of invader species such as dandelion and goatsbeard to be present. This creates more competition for bluebunch wheatgrass and other decreaser grasses; making it difficult for them to quickly respond to a change in grazing management alone. Therefore, an input of energy is required for the community to return to the Reference State (1). Wind and water erosion may be eroding soil from the plant interspaces. Soil fertility is reduced and soil surface erosion resistance has declined compared to the Reference State (1).
Long-term grazing mismanagement with continuous growing-season pressure will reduce total productivity of the site and lead to an increase of bare ground. Suppression of fire can also promote shrub growth, increasing plant interspaces. Once plant cover is reduced, the site is more susceptible to erosion and degradation of soil properties. Soil erosion or reduced soil fertility will result in reduced plant production. This soil erosion or loss of soil fertility indicates the transition to the Altered State (2), because it creates a threshold requiring input of energy to return to the Reference State (1). Transition to the Mixed Sagebrush Community Community (2.1) may be exacerbated by extended drought conditions.
Big sagebrush steppe communities historically had moderate fuel loadings and were characterized by 10 to 70 year interval (often less than 30 years), fires that produced a mosaic of burned and unburned lands (Bunting, et.al. 1987). Following fire on the fine-textured soils, the perennial bunchgrasses recovered in a few years and were present to fuel a subsequent fire. Conversely, extensive wildfires burning under hot-dry conditions would have resulted in nearly complete destruction of scattered sagebrush (Arno and Gruell 1983). Winterfat is tolerant of low intensity fire but will kill with a hot fire (Pellant 1984).
This community crossed a threshold from the Mixed Bunchgrass Community (1.2) due to the erosion of soil, vegetation composition, loss of soil fertility, or degradation of soil conditions. This results in a critical shift in the ecology of the site. The effects of soil erosion can alter the hydrology, soil chemistry, soil microorganisms, and soil structure to the point where intensive restoration is required to restore the site to another state or community. Changing grazing management, alone, may not create sufficient improvement to restore the site if decreaser species are greatly reduced. Dormaar (1997) stated that with decreased grazing pressure, a needle and thread plant community did not change species composition but the content of the soil carbon increased. It will require a considerable input of energy to move the site back to the Reference State (1). This state has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts, i.e., soil rebuilding, intensive mechanical treatments, and reseeding.
The transition to this state could result from overgrazing and fire suppression, especially repeated early season grazing coupled with extensive drought. If heavy grazing continues, plant cover, litter, and mulch will continue to decrease and bare ground will increase exposing the soil to accelerated erosion. Litter and mulch will move off-site as plant cover declines. The Mixed Sagebrush Community will then shift to a Shortgrass-Shrub Community (2.2). Continued overgrazing will drive the community to a Degraded State (3). Introduction or expansion of invasive species will further drive the plant community to the Invaded State (4).
Community 2.2
Shortgrass-Shrub Community
With continued mismanagement of grazing, especially coupled with prolonged drought, Idaho fescue will decrease in vigor. The bunchgrasses will decline in production as plants die or become smaller, and species with higher grazing tolerance (such as western wheatgrass) increase in vigor and production as they respond to resources previously used by the bunchgrasses. These less desirable, shorter rooted species will become codominant with the bunchgrasses. Midstatured grasses such as bluebunch wheatgrass, Columbia needlegrass, and green needlegrass will exist within taller shrubs where they are protected from grazing animals. Shrubs will become more competitive for limited moisture as bare ground and soil erosion increase. This state may exhibit conditions where livestock and wildlife are also overconsuming shrubs.
Pathway 2.1A
Community 2.1 to 2.2
The driver for community shift 2.1A is continued overgrazing. Overgrazing on this site is defined by grazing utilization over 60 percent or season long grazing where livestock can graze regrowth. This shift is triggered by continued loss of bunchgrass vigor, especially the remaining Idaho fescue and needlegrasses. The mid- and short-statured grasses will become more competitive and become co-dominant with the bunch grasses. Shrubs will increase in canopy cover to 25 to 30 percent. A shift in shrub dominance of big sagebrush to three-tip sagebrush (Artemisia tripartita) may also occur.
Pathway 2.1B
Community 2.2 to 2.1
If grazing management is implemented, Idaho fescue may regain its vigor and move towards the Mixed Sagebrush Community (2.1). This will give grasses an advantage over invading shrubs before too much competition takes place. Since the transition from Plant Community 2.1 to Plant Community 2.2 was likely caused by repeated heavy utilization, a conservative grazing plan where utilization is reduced at or below moderate utilization with rest or deferment is incorporated. Van Poolen and Lacey (1979) found that forage production increased by an average of 35 percent on western ranges when converting from heavy utilization to moderate utilization (less than 50 percent). Shrub removal and favorable growing conditions can accelerate this process. If the site contains excess Wyoming big sagebrush (Artemisia tridentata spp. Wyomingensis), a low intensity fire or mechanical treatment (Wambolt 1986) could reduce shrub competition and allow for increased vigor and the reestablishment of grass species.
State 3
Degraded State
The Degraded State is characterized by a near complete lack of mid-statured bunchgrasses. Idaho fescue, needle and thread, Sandberg bluegrass and prairie Junegrass are dominant grasses. Increaser shrubs nearly replace larger shrub species. Remaining larger shrub species are heavily hedged and may have been replaced with three-tip sagebrush. This state is likely a terminal state (e.g. restoration is impossible or unsuccessful without major financial and energy inputs).
Community 3.1
Shortgrass Community
This state is characterized by soil surface degradation and little plant soil surface cover. Soil loss continues and subsequent loss of soil organic matter create conditions where native perennial grasses are reduced. Grass and forb cover may be sparse with obvious rill erosion between plant bases.
Needle and thread and Idaho fescue exist in small patches. This could occur due to overgrazing (failure to adjust stocking rate to declining forage production due to increased invasive dominance), long-term lack of fire (if dense Wyoming big sagebrush occurs), or introduction of invasive species.
In the most severe stages of degradation, there is a significant amount of bare ground, and large gaps occur between plants. Potential exists for soils to erode to the point that irreversible damage may occur. This is a critical shift in the ecology of the site. Soil erosion combined with lack of organic matter deposition due to sparse vegetation create changes to the hydrology, soil chemistry, soil microorganisms, and soil structure to the point where intensive restoration is required to restore the site to another state or community. Changing management (i.e., improving grazing management) cannot create sufficient change to restore the site.
The forb component changes to be dominated by spiny phlox (Phlox hoodii) and shrub canopy cover is usually greater than 20 percent. Big sagebrush is replaced with a dominant community of low sagebrush (Artemisia arbuscula), three-tip sagebrush, broom snakeweed, rubber rabbitbrush, fringed sagewort, and plains pricklypear cactus. This state has lost soil or vegetation attributes to the point that recovery to the Reference State will require extensive reclamation efforts, i.e. soil rebuilding, intensive mechanical treatments, and reseeding. Grazing management such as a rest rotation will not return this state to Reference without reclamation efforts.
This plant community may be in a terminal state that will not return to the reference state because of degraded soil conditions and loss of higher successional native plant species.
Key factors of approach to transition: Decrease in grass canopy cover and production, increase of shrub canopy cover, increases in mean bare patch size, increases in soil crusting, decreases in cover of cryptobiotic crusts, decreases in soil aggregate stability, and/or evidence of erosion including water flow patterns and litter movement.
State 4
Invaded State
The Invaded State is identified by being in the exponential growth phase of invader abundance where control is a priority. Dominance (or relative dominance) of noxious/invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A 10 percent invasive species composition by dry weight indicates the point that a substantial energy input, such as herbicide or mechanical removal, will be required to create a shift to the grassland state, even with a return to proper grazing management or favorable growing conditions. Prescriptive grazing that specifically focuses on grazing of the invasive plant can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain species composition of invasive species.
Community 4.1
Invaded Community
Communities in this state may be structurally indistinguishable from the Reference State except that invasive/noxious species exceed 10 percent of species composition by dry weight. This state may also include a community similar to the Degraded State (3) except that invasive/noxious species exceed 10 percent of species composition by dry weight. Although there is no research to document the level of 10 percent, this is estimated to be the point in the invasion process following the lag phase based on interpretation of Masters and Sheley, 2001. For aggressive invasive species (i.e., spotted knapweed) the threshold could be less than 10 percent. Early in the invasion process there is a lag phase where the invasive plant populations remain small and localized for long periods before expanding exponentially (Hobbs and Humphries 1995).
Production in the invaded community may vary greatly based on the severity of invasion and potential subsequent effects on species composition. A site dominated by Kentucky bluegrass or spotted knapweed, where soil fertility and chemistry remain near reference, may have production near that of the reference community. A site with degraded soils and an infestation of cheatgrass may produce only 10 to 20 percent of the reference community.
Once invasive species dominate the site, either in species composition by weight or in their impact on the community the threshold has been crossed to the Invaded State (4). As invasive species such as spotted knapweed, cheatgrass, and leafy spurge become established, they become very difficult to eradicate. Therefore considerable effort should be placed in preventing plant communities from crossing the threshold to the Invaded State (4) through early detection and proper management. Preventing new invasions is by far the most cost-effective control strategy, and typically places an emphasis on education. Control measures used on the noxious plant species impacting this ecological site include chemical, biological, and cultural (burning, mowing, cutting) control methods. The best success has been found with an integrated pest management (IPM) strategy that incorporates one or several of these options along with education and prevention efforts (DiTomaso 2000)
State 5
Conifer Encroached State
Rocky Mountain juniper (Juniperus scopulorum) and Douglas fir (Pseudotsuga menziesii) encroachment is common on this ecological site and is generally focused in areas with east and north facing slopes. Under the Reference State, conifers may exist on this site however this is limited to two trees per acre on north and east facing slopes and is considered a trace canopy cover.
Conifer encroachment likely occurs in the late stages of the Altered State (see State-and-transition model) where there is an increase of bare ground and reduced vigor of mid-statured bunchgrasses due to a combination of factors. Fire suppression and improper grazing management are the two most common triggers. The exact conditions in which juniper begins to encroach vary, however the trend points to a combination of 1 or more of the following; moderately heavy to heavy grazing, reduced (non-existent) fire frequency, increased atmospheric carbon, and generally warmer climate (compared to that of pre-settlement). When heavy grazing occurs areas in the plant canopy open allowing for seed dispersal by bird or overland flow via rills on neighboring sites. The effects of conifer encroachment are not immediately noticed however over time as conifer canopy increases; light and water interception increase which reduce opportunities for herbaceous plants. One paper (Barrett, 2007) suggests that for precipitation to penetrate the juniper canopy, events must be greater than 0.30 inches. Increase juniper canopy creates perching sites for predators which reduces site suitability for greater sage grouse.
Studies (Miller et al 2000) based in a similar community to the Conifer Encroached communities of this LRU suggest following a phased approach to characterize the stand. Not unlike the Western Juniper community discussed in Miller et al, these communities of Montana exhibit 3 different phases based, at this time, on qualitative information.
Community 5.1
Conifer Community Phase I
Figure 11. Early Phase of conifer encroachment on the Droughty Steep Ecological Site in the Blacktail Mountains of SW Montana
Phase I (Early) is defined by actively expanding conifer cover with less than 5 percent canopy cover; trees limbs will touch the ground. This early stage has not lost its hydrologic functions, however herbaceous plant communities may show signs of reduced production and species richness. Control methods include mechanical removal and prescribed fire. Prescribed fire is still effective management in this phase as it still contains the necessary native plants for recovery. The tree canopy density is low enough that risk of a dangerously hot fire is reduced.
Community 5.2
Conifer Community Phase II
Phase II (Mid Stage) is still actively expanding, however canopy cover may reach up to 15 percent. Due to the more mature trees present, seed production is very high. This Mid Phase begins to highly restrict herbaceous and shrubby cover. Conifers tend to be codominant with herbaceous plants. Hydrology is departing from reference with rills becoming longer and, in isolated areas, erosional gullies may begin to form. Control methods of the Mid Stage should focus on mechanical treatment (chainsaw cutting or mastication) as there is a high risk of catastrophic and potentially hot, sterilizing fire. Post treatments of slash are currently being evaluated but typically include chipping, lop-and-scatter, and slash piling. Lop-and-scatter and slash pile treatments are often burned to remove excess woody debris. Qualitative assessments of these treatments suggests native bunchgrasses respond immediately in this stage. Post treatment grazing management including two growing seasons of rest may be necessary while these plants increase their basal area.
Community 5.3
Conifer Community Phase III
Phase III (Late stage) is where juniper cover exceed 20 percent and has slowed to resemble a forest condition. Lower limbs of trees begin to die and the rangeland shrub cover is nearly lost. Travel through this community is increasingly difficult. Conifers become the dominant plant with herbaceous plant production greatly decreased. Bare ground increases and hydrologic function is nearly lost compared to a grass/shrub community. Late Stage Phase should focus more on restoration than control as the necessary plants will likely not be present to cross the threshold back to the Reference State. Site stability and hydrologic function are lacking in this phase so mechanical removal of conifer will be necessary and prescribed fire is not suggested. Post treatment rest from grazing is important as remaining native grasses will be reduced in stature and will be susceptible to accidental overgrazing as livestock will seek out these tender plants. After a rest period, light and brief grazing may help initiate tillering of bunchgrasses.
Pathway 5.1A
Community 5.1 to 5.2
Over time Phase I community expands to increase in both height and width. The driver for this pathway is primarily lack of fire however heavy grazing (utilization that exceeds 50 percent) can help reduce herbaceous competition and expose soil for seed contact. Increase atmospheric carbon dioxide has also been shown to increase coniferous tree and shrub growth (Archer et al. 2017).
Pathway 5.2B
Community 5.2 to 5.3
Over time Phase II community expands to increase in both height and width. The driver for this pathway is primarily lack of fire however heavy grazing (utilization that exceeds 50 percent) can help reduce herbaceous competition and expose soil for seed contact. Increase atmospheric carbon dioxide has also been shown to increase coniferous tree and shrub growth (Archer et al. 2017).
Transition T1B
State 1 to 2
The Reference State (1) transitions to the Altered State (2) if bluebunch wheatgrass decreases to 15 percent, by dry weight, or if bare ground cover increases by 10 percent. The driver for this transition is loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Altered State.
There are several other key factors signaling the approach of transition T1B: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability or evidence of erosion including water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management and long-term drought leading to a decrease in bluebunch wheatgrass composition to 15 percent and reduction in total plant canopy cover.
Transition T1C
State 1 to 3
The Reference State (1) transitions to the Degraded State (3) when bluebunch wheatgrass is completely removed from the plant community. Idaho fescue and needle and thread are subdominant to short-statured bunchgrasses such as Sandberg and Cusick's bluegrass. The trigger for this transition is loss of most mid-statured bunchgrasses, which creates open spaces with bare soil. Soil erosion as a result of increased bare ground and shallow roots decreases soil fertility, driving transitions to the Degraded State. There are several other key factors signaling the approach of transition T1C: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability and/or evidence of erosion including rills, water flow patterns, development of plant pedestals, and litter movement. The driver for this transition is improper grazing management, intense or repeated fires, or heavy human disturbance. Rapid transition is generally realized where livestock are confined to small pastures for long periods of time such as feeding areas, horse pastures, and bull lots.
Degradation may be so extreme that traditional restoration methods may not be successful and require extensive mechanical and financial inputs.
Transition T1D
State 1 to 4
Healthy plant communities are most resistant to invasion however, sometimes regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control), the Reference State (1) can transition to the Invaded State (4) in the presence of aggressive invasive species such as spotted knapweed, leafy spurge, and cheatgrass. The Central Rocky Mountains tend to resists invasion however recent dry climate cycles, repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for encroachment. Long-term stress conditions for native species (e.g., overgrazing, drought, and fire) accelerate this transition. If populations of invasive species reach critical levels, the site transitions to the Invaded State. The trigger for this transition is the presence of aggressive invasive species with invasive species composition by dry weight approaching 10 percent.
Transition T1E
State 1 to 5
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds and/or other viable material of these tree species.
Restoration pathway R2A
State 2 to 1
The Altered State (2) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, or revegetation. Examples of mechanical treatment may be brush control while cultural treatments may include prescribed grazing, targeted brush browsing, or prescribed burning. Grazing practices that promote bluebunch wheatgrass is primarily light to moderate grazing during the critical season (late June through July) or fall and dormant season of moderate however heavy utilization may not have negative impacts (Dormaar and Willms 1998) though grazing should match the species composition of the site prior to exceeding moderate utilization.
Low intensity prescribed fires to reduce competitive increaser plants such as needle and thread and Sandberg bluegrass. A low intensity fire will also reduce big sagebrush densities. In areas with potential of annual grass infestation, fire should be carefully planned or avoided. The drivers for this restoration pathway are reclamation efforts along with proper grazing management.
| Brush Management |
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| Prescribed Burning |
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| Fence |
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| Livestock Pipeline |
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| Prescribed Grazing |
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| Grazing Land Mechanical Treatment |
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| Range Planting |
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Transition T2A
State 2 to 3
As improper grazing continues vigor of bunchgrasses will decrease, and the shorter grasses and shrubs will increase towards the Degraded State (3). Improper grazing management for this state can be defined as grazing events that exceed moderate grazing (40 to 50 percent grazing use), grazing season that exceeds half of the growing season, and/or grazing events that consume the plant regrowth in the same growing season. Highly managed grazing events that exceed moderate grazing levels for short timeframes are generally not included in this definition due to increased rest periods between these grazing events.
Additionally, prolonged drought will provide a competitive advantage to shrubs allowing them to become co-dominant with grasses. Shrub canopy will increase however shrubs will express low growth forms. Mat forming forbs will also increase.
Key transition factors: increase of native shrub canopy cover; reduction in bunchgrass production; decrease in total plant canopy cover and production; increases in mean bare patch size; increases in soil crusting; decreases in cover of cryptobiotic crusts; decreases in soil aggregate stability; and/or evidence of erosion including water flow patterns and litter movement.
Transition T2B
State 2 to 4
Invasive species can occupy the Altered State (2) and drive it to the Invaded State (4). The Altered State is at risk if invasive seeds and other viable material are present. The driver for this transition is more than 10 percent dry weight of invasive species. The trigger is the presence of seeds and other viable material of invasive species.
Transition T2D
State 2 to 5
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds and/or other viable material of these tree species.
Restoration pathway R3B
State 3 to 1
The Degraded State (3) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts, such as soil rebuilding, intensive mechanical treatments, or revegetation. Studies suggest (Whitford et al 1989) a mulch with high carbon to nitrogen ratio such as wood chips or bark in low moisture scenarios can be beneficial for slow mobilization of plant available nitrogen. Biochar may also be added to the system to improve Soil Organic Carbon (SOC) which should improve Cation Exchange Capacity (CEC), microbial activity, and hydrologic conductivity (Stavi 2012). The drivers for the restoration pathway are removal of increaser species, restoration of native bunchgrass species, persistent management of invasives and shrubs, and proper grazing management. Without continued control, invasive and shrub species are likely to return (probably rapidly) due to presence of seeds and other viable material in the soil and management related increases soil disturbance.
| Brush Management |
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| Prescribed Burning |
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Restoration pathway R3A
State 3 to 2
Since the deep-rooted bunchgrass plant community has been removed, restoration to the Altered State (2) is unlikely unless a seed source is available. If a sufficient amount of bunchgrass remains on the site, chemical application or biological control in conjunction with proper grazing management, can reduce the amount of shrubs and invasive species and restore the site to the Shortgrass Community (2.2). Grazing management strategies that follow light grazing and allow for long periods of rest will allow for limited recovery of remaining bunchgrasses, however grazing management alone may not directly result in restoration. Restoration methods such as reseeding may be necessary
Low intensity fire can be utilized to reduce shrub competition and allow the reestablishment of grass species. Caution must be used when considering fire as a management tool on sites with fire tolerant shrubs such as rubber rabbitbrush, as these shrubs will re-sprout after a burn. Broom snakeweed and fringed sagewort may or may not re-sprout depending on conditions (USDA Forest Service 2011).
Transition T3A
State 3 to 4
Invasive species can occupy the Degraded State (3) and drive it to the Invaded State (4). The Degraded State is at risk of this transition occurring if invasive seeds or viable material are present. The driver for this transition is presence of critical population levels of invasive species. The trigger is the presence of seeds or viable material of invasive species. This state has sufficient bare ground that the transition could occur simply due to presence or introduction of invasive seeds or viable material. This is particularly true of aggressive invasive species such as spotted knapweed and cheatgrass. This transition could be assisted by overgrazing (failure to adjust stocking rate to declining forage production), long-term lack of fire, or extensive drought.
Transition T3C
State 3 to 5
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds and other viable material of these tree species.
Restoration pathway R4C
State 4 to 1
Restoration of the Invaded State (4) to the Reference State (1) requires substantial energy input. The drivers for the restoration pathway are removal of invasive species, restoration of native bunchgrass species, persistent management of invasive species, and proper grazing management. Without continued control, invasive species are likely to return (probably rapidly) due to the presence of seeds and other viable material in the soil and management related practices that increase soil disturbance. If invaded by conifer encroachment, treatment depends on the condition of the rangeland. See Plant community 4.1 for alternative measures of restoration.
Sites that have transitioned from the Degraded State (3) to the Invaded State (4) may be severely lacking soil and vegetative properties that will allow for restoration to the Reference State. Hydrologic function damage may be irreversible especially with accelerated gully erosion.
Restoration pathway R4B
State 4 to 2
If invasive species are removed before remnant populations of bunchgrasses have been drastically reduced the Invaded State (4) can return to the Altered State. The driver for the reclamation pathway is weed management with possible reseeding. Continued Integrated Pest Management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life. The trigger is invasive species control.
Restoration pathway R4A
State 4 to 3
If invasive species are removed the site could return to the Degraded State (3). Without sufficient remnant populations of preferred plants the Invaded State (4) is not likely to return to any of the other states. The driver for the reclamation pathway is weed management without reseeding. The trigger is invasive species control. The invading species cause a significant increased soil loss due to lack of ground cover (Lacey et al. 1989).
Transition T4B
State 4 to 5
Canopy cover of conifer tree/shrub cover exceeds two stems per acre. The threshold change is triggered by the presence of seeds and other viable material of invasive species.
Restoration pathway R5A
State 5 to 1
Depending on the level of conifer canopy cover and its impact on rangeland health, restoration efforts may be simply focus on removal of coniferous trees and shrubs to restore the Conifer Encroached State (5) to the Reference State (1).
If utilizing the phases established by Miller et al., management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers via Brush Management or Prescribed fire combined. If mechanical removal of conifers is utilized, no grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment and/or rest is suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
Restoration pathway R5B
State 5 to 2
The Conifer Encroached State (5) Phases I and II will often resemble early stages of the Mixed Sagebrush Community (2.1) of the Altered State (2). If utilizing the phases established by Miller et al., management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers via Brush Management or Prescribed fire combined. If mechanical removal of conifers is utilized, no grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment and/or rest is suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
Restoration pathway R5C
State 5 to 3
The Conifer Encroached State (5) Phases II and III will likely resemble the Degraded State (3) on this site due to reduced mid-statured bunchgrasses. If utilizing the phases established by Miller et al management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al. This Restoration Pathway is exceedingly rare as it is typically not cost effective for land managers to manage for a degraded state.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers via Brush Management and/or Prescribed fire combined. If mechanical removal of conifers is utilized, no grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment and/or rest is suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
Restoration pathway R5D
State 5 to 4
If utilizing the phases established by Miller et al management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al. This Restoration Pathway is exceedingly rare as it is typically not cost effective for land managers to manage for the Invaded State.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers via Brush Management or Prescribed fire combined. If mechanical removal of conifers is utilized, no grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment or rest is suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is absolutely necessary with presence of invasive herbaceous species.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
