Ecological dynamics
The Sandy (Sy) 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 Crazy-Beartooth LRU of MLRA 46X, Subset B is found where an Ustic soil moisture regime occurs. This area is typified by a frigid soil temperature regime which receives a yearly representative value of 15 to 19 inches of relative effective annual precipitation and between 70 and 110 consecutive frost-free days annually. The Sandy ecological site is characterized by being not strongly or violently effervescent in the top 4 inches (10cm) of the soil surface, having coarse sandy loam to fine sandy loam surface textures, having less than 35 percent rock fragments in the 10 to 20 inch control section. If present, an argillic horizon will have less than 20 percent clay.
The majority of precipitation falls as rain from April through July. Primary growth typically occurs between May and early July. Dominant plants are those 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 among this cool season dominated plant community if adequate precipitation is present.
As the Sandy ecological site occurs across a relatively large landscape, slight variations within the plant community occur due to elevation, frost-free days, and relative effective annual precipitation. The reference plant community is heavily dominated by big bluestem, little bluestem, bluebunch wheatgrass (Pseudoroegneria spicata), green needlegrass (Nassella viridula), prairie sandreed (Calamagrostis longifolia), and Idaho fescue (Festuca idahoensis). Spike fescue and rough fescue may also be present however there presence is sometimes lacking as this area is on the fringes of each plant's habitat. Subdominant species may include muhly (Muhlenbergia spp), winterfat (Krascheninnikovia lanata), rabbitbrushes (Ericameria and Chrysothamnus), and common snowberry (Symphoricarpus albus). This potential is suggested by investigations showing a predominance of perennial grasses on near-pristine range sites (Ross et al. 1973). In the reference plant community, shrubs are a relatively minor vegetative component.
A shift to dominance of shrubs may occur in response to improper grazing management or extended drought. Improper grazing management is typically defined as allowing multiple grazing events that take more than half of the current year's growth without allowing rest and recovery. Shrub encroachment by a variety of species, including, broom snakeweed (Gutierrezia sarothrae), fringed sagewort (Artemisia frigida), Sagebrushes (Artemisia ssp), rubber rabbitbrush (Ericameria nauseosa), yellow rabbitbrush (Chrysothamnus viscidiflorus) and plains prickly pear (Opuntia polyacantha) occur within this site as the mid-statured bunchgrasses decrease. Shrub dominance and grass loss can be associated with soil erosion and ultimately thinning of the native soil surface. Subsequent loss of soil could lead to a Degraded State.
Historical records indicate, prior to the introduction of livestock (cattle and sheep) during the late 1800’s, elk and bison grazed this ecological site. Due to the nomadic nature and herd structure of bison, areas that were grazed received periodic high intensity short duration grazing pressure.
Natural fire as well as prescribed fire utilized by indigenous peoples was a major ecological driver of this entire ecological site. Fire tended to restrict tree and shrub growth to small patches and promoted an herbaceous plant community. The natural fire return interval was highly variable however it was likely shorter than 30 years. With the historically recent, since 1910, suppression of fire, shrubs and coniferous trees have increased significantly.
Due to relatively neutral to slightly alkaline pH of the soils on this site; the potential for farming is high. Hay and small grains production has constituted the largest replacement of native vegetation on this site with introduced cool-season annual crops (wheat, barley, oats), perennial introduced grass species and legumes (e.g., alfalfa) being best adapted. This ecological site has also been converted to pastureland usually perennial grasses and legumes for grazing. Cropland, pastureland, and hayland are intensively managed with annual cultivation, annual harvesting, and/or frequent use of herbicides, pesticides, and commercial fertilizers to increase production. Where irrigation water is available, this site is highly productive.
Dense clubmoss (Selaginella densa), in general, is a minor component of Reference plant community of the Sandy 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). The site could also be an old crop fields that have reverted back to rangeland. In this case, clubmoss is helping reduce erosion and increase site stability especially where livestock use is restricted (such as CRP). While dense clubmoss provides soil stability on the sites it exists, a common misconception is that it competes for the limited water resources into the upper soil profile which restricts plant available water however a study from Canada (Colberg and Romo 2003) in a similar climate 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 may, however, 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), Sulphur cinquefoil (Potentilla recta), cheatgrass (Bromus tectorum), field brome (Bromus arevensis), yellow toadflax (Linaria vulgaris), Dandelion (Taraxicum spp), and Kentucky bluegrass (Poa pratensis). Invasive weeds are beginning to have a high impact on this Ecological Site often as a result of human impacts such as mismanaged grazing, recreation, and urban development.
Plant Communities and Transitions
A State and Transition Model for this Sandy 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 full 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. 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.
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 el al. 2003, Bestelmeyer et al. 2004, Bestelmeyer and Brown 2005, Stringham et al. 2003.
State 1
Reference State
The Reference State of the Sandy ecological site consists of two known potential plant communities 1.1 Mixed Bunchgrass Community and 1.2 Bluebunch Community. These are generally characterized by a mid-statured bunchgrass communities with limited shrub production. Community 1.1 is dominated by bluebunch wheatgrass, big bluestem, and little bluestem with limited rough and spike fescue while Community 1.2 has a codominance of bluebunch wheatgrass, bluestems, with an increase in Idaho fescue and needle and thread.
Community 1.1
Mixed Bunchgrass Community
In the Mixed Bunchgrass Community, bluebunch wheatgrass (Pseudoroegneria spicata), green needlegrass (Nassella viridula), big bluestem (Andropgon gerardii), little bluestem (Schizachyrium scoparium), and needle and thread (Hesperostipa comata) are typically dominant. Limited rough and spike fescue may be present with Indian ricegrass (Achnatherum hymenoides) and winterfat (Krascheninnikovia lanata) as subordinates in the community. Shrub species (silver sagebrush, fringed sagewort, broom snakeweed) remain a minor part of the community. Sandberg bluegrass (Poa secunda), Idaho fescue (Festuca idahoensis) and dryland sedges are also common. This state occurs on areas with proper livestock grazing or in areas with little or no grazing pressure. Bluebunch wheatgrass lacks resistance to grazing during the critical growing season (spring) 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 Reference State 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.
As discussed in the Ecological Dynamics section natural fire regime restricted shrubs to relatively small portions of the Reference Plant Community 1.1. Shrub species present may include silver sagebrush, spineless horsebrush, winterfat, tarragon (Artemisia drucunculus), and fringed sagewort. Infrequent fire probably maintained communities as open, seral stands of productive herbaceous species with patches of shrubs.
Community 1.2
Bluebunch Community
With proper grazing management over time, the Bluebunch Community (1.2) can come close to the diversity and complexity of the Mixed Bunchgrass Community (1.1). Without active management the site is not likely to return to near Reference Plant Community.
Western wheatgrass and needle and thread tolerate grazing pressure better than the bluestems, rough fescue and bluebunch wheatgrass. The growing point for these grasses is several inches above the ground, making it very susceptible to continued close grazing (Smoliack, et al 2006) while western wheatgrass and needle and thread growing points tend to be near the plant base. These plants increase in composition when more palatable and less grazing tolerant plants decrease due to improper grazing management. Needle and thread, western wheatgrass, and bluebunch wheatgrass share dominance in the Bluebunch Community (1.2). Other grass species, which are more tolerant to grazing and are likely to increase compared to the Mixed Bunchgrass Community, include Sandberg bluegrass (Poa secunda), prairie Junegrass, thickspike wheatgrass (Elymus lanceolatus) and blue grama (Bouteloua gracilis). Some increaser forbs species include western yarrow, hoods phlox (Phlox hoodii), scarlet globemallow (Sphaeralcea coccinea), hairy goldenaster (Heterotheca villosa), and pussytoes (Antennaria spp.). Fringed sagewort (Artemisia frigid) is a shrub that also increases under prolonged drought or heavy grazing and can respond to precipitation that falls in July and August.
Heavy continuous grazing will reduce plant cover, litter, and mulch. Timing of grazing is important on this site because of the moisture limitations beyond June, especially on the drier sites. Bare ground will increase and expose the soil to erosion. Litter and mulch will be reduced as plant cover declines. As long as the production of bluebunch wheatgrass remains a significant portion of the total biomass production, the site can return to the Bluebunch Wheatgrass Community (Pathway 1.2A) under proper grazing management and favorable growing conditions.
The Bluebunch Community (1.2) is the At-Risk Plant Community for the Sandy 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 Bunchgrass State (2) or the Degraded State (3). Until the Bluebunch Community (1.2) crosses the threshold into the Needle and thread Community (2.1) or the Invaded Community (4.1), this community can be managed toward the Mixed Bunchgrass Community (1.1) using prescribed grazing and strategic weed control (if present). It may take several years to achieve this recovery, depending on growing conditions, vigor of remnant bluebunch wheatgrass plants, and the aggressiveness of the weed treatments.
Pathway 1.1A
Community 1.1 to 1.2
Big bluestem, rough fescue and bluebunch wheatgrass lose vigor with improper grazing or extended drought. When vigor declines enough for plants to die or become smaller, species with higher grazing tolerance increase in vigor and production as they access the resources previously used by rough fescue. Decrease of species composition by weight of bluestems, rough fescue and to a lesser extent bluebunch wheatgrass indicates that the plant community has shifted to the Bluebunch 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 tall bunchgrasses, 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. Since needle-and-thread normally heads out in June and rough fescue and bluebunch wheatgrass in early July and bluestems in mid to late July, this should be taken into consideration when planning grazing management.
Pathway 1.2A
Community 1.2 to 1.1
The Bluebunch Community (1.2) will return to the Mixed Bunchgrass 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 mixed tall bunchgrass dominated state. The driver for this community shift (1.2A) is increased vigor of the bluestems, fescues, and bluebunch wheatgrass are equals in species composition. The trigger for this shift is the change in grazing management favoring rough fescue. In general, conservative grazing management styles such as deferred or rest rotations utilizing moderate grazing (less than 50% use) coupled with favorable growing conditions like cool, wet springs are these triggers. These systems tend to promote increases in soil organic matter which promotes microfauna and can increase 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 rough fescue and 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.
State 2
Altered State
The Altered State is characterized by having less than 15 percent tall bunchgrasses by dry weight. It is represented by two communities that differ in the percent composition of needle and thread, 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/or heavy grazing practices. A few of these species may include needle and thread, Sandberg bluegrass, scarlet globemallow, hairy goldenaster, and fringed sagewort.
Community 2.1
Needle and thread Community
Long-term grazing mismanagement with continuous growing-season pressure will reduce total productivity of the Sandy ecological site and lead to an increase of bare ground. Once plant cover is reduced, the site is more susceptible to erosion and degradation of soil properties. Soil erosion or reduced soil health 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 Needle and thread Community (2.1) may be exacerbated by extended drought conditions.
Needle and thread dominates this Community (2.1). Tall, decreaser bunchgrasses makes up less than 15 percent of species composition by dry weight and the remaining plants tend to be scattered and low in vigor. Increaser and invader species will be more common and create more competition for tall, decreaser bunchgrasses. This makes it difficult for these species 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).
This community crossed a threshold compared to the Bluebunch 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 cannot create sufficient improvement to restore the site within a reasonable time frame. Dormaar (1997) stated that with decreased grazing pressure a needle-and-thread/blue grama 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/or reseeding.
The transition to this state could result from overgrazing, 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. Continued improper grazing 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).
State 3
Degraded State
The Degraded State is described by a single plant community consisting of nearly equal components of increaser grasses, shrubs, and forbs. Large patches of bare ground exist with areas of erosional pedestalling and terracettes common. Dense clubmoss (Selaginella densa) exists between plant bases as a reaction to the increased bare ground
Community 3.1
Shortgrass/Rhizomatous Community
Soil loss continues or increases with grass and forb cover becoming very sparse or clumped (canopy cover less than 30 percent). Weeds, annual species, cacti, or shrubs dominate the plant community. Mid-stature perennial bunchgrass species (e.g., needle and thread) may exist, but only 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 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. Large patches of prickly pear cactus are common. 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 within a reasonable time frame.
This state is characterized by soil surface degradation and little plant soil surface cover. Shrub canopy cover is usually greater than 15 percent. In this plant community, big sagebrush is replaced with a dominant community of broom snakeweed, rabbitbrush, fringed sagewort, and plains pricklypear cactus. This State has lost soil or vegetation attributes to the point that recovery to the Bunchgrass Grassland State will require reclamation efforts, i.e. soil rebuilding, intensive mechanical treatments, and/or reseeding.
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 the exponential growth of invader abundance where control is a priority. Dominance (or relative dominance) of noxious or invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A level of 20 percent invasive species composition by dry weight indicates the point that a substantial energy input will be required to create a shift to the grassland state (herbicide, mechanical treatment) even with a return to proper grazing management or favorable growing conditions. Prescriptive grazing 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.
These communities within this state will follow a pathway if the invasive/noxious species will continue to thrive without mechanical, biological, or chemical control methods to exceed 50 percent of species composition by dry weight. The invasive nature of the weed out-competes the present plant community. Once the weed reaches maximum population level for this site, effective control is unlikely without massive resource inputs. Ecological processes of the site may change after invading species have established and spread (Walker and Smith 1997).
Community 4.1
Non Native Invaded Community
Communities in the Non Native Invaded State may be structurally indistinguishable from the Bunchgrass State except that invasive/noxious species exceed 20 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 20 percent of species composition by dry weight. Although there is no research to document the level of 20 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) a 20 percent 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. 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 a 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 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
The Conifer Encroached State is still being researched however it may contain as many as four different communities.
Community 5.1
Conifer Community
Rocky Mountain juniper (Juniperus scopulorum), Ponderosa pine (Pinus ponderosa), limber pine (Pinus flexilis), and Douglas fir (Pseudotsuga menziesii) encroachment is common on this ecological site and is generally focused in on areas where the mountains of MLRA 43B transition quickly to MLRA 46. Under the Reference State, no conifers should exist on this site. It is also noted that all States may transition to the Conifer Encroached State however encroachment is most likely to occur in the the Altered State (see state-and-transition model) where there is an increase of bare ground due to a combination of factors that allows seed-to-soil contact with reduced competition. Fire suppression and improper grazing management are the two most common triggers. The exact mode in which conifers begin to encroach varies however the trend points to a combination of 1 or more of the following: repeated 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 tree canopy creates perching sites for predators which reduces site suitability for greater sage grouse. More information is needed on the full extent and impact of juniper encroachment on this plant communities for an approved Ecological Site Description.
Studies (Miller et al 2000) based in a similar to the Rocky Mountain Juniper community of Montana suggest following a phased approach to characterize the juniper stand. Not unlike the Western Juniper community discussed in Miller et al, the Rocky Mountain juniper communities of Montana exhibit three or four different phases based, at this time, on qualitative assumptions.
Phase I (Early) is defined by actively expanding juniper cover with generally less than 10 percent canopy cover and the trees’ limbs generally touch the ground. This early stage generally has not completely 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 in this phase as it still contains the necessary native plants for recovery. The tree canopy is also low enough that risk of a dangerously hot fire is reduced.
Phase II (Mid Stage) is still actively expanding however canopy cover may reach up to 15-25 percent and due to the more mature trees seed production is very high. This Mid Phase begins to highly restrict herbaceous and shrubby plant and junipers tend to be codominant. Hydrology is departing from reference with rills becoming longer and in isolated areas erosional gullies may exist. Control methods of the Mid Stage should focus on mechanical treatment as there is a high risk of catastrophic and potentially sterilizing fire.
Phase III (Late stage) is where juniper cover exceed 25 percent and has slowed as a forest condition. Lower limbs of trees begin to die and the shrub cover is nearly lost. Traveling through this community is increasingly difficult. Junipers 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 a rangeland situation. The soil stability and hydrologic function are lacking in this phase so mechanical removal of juniper will be necessary.
Phase IV (Closed) is the steady state forest where the system is nearly absent of rangeland plants. The trees stop producing seed and begin to close in on each other. This phase is impassible and nearly all light and precipitation are intercepted. Bare ground is high and soil chemistry slowly changes due to acidification from juniper. Within this LRU, the closed phase is extremely rare due to two reasons: 1) this phase takes upwards of 100 years to occur 2) management often occurs before trees are allowed to reach this phase. The presence of sagebrush stumps indicates the historical plant community as rangeland which will prevent misclassification of historic Juniper Forests (often greater than 100 years of age).
Transition T1A
State 1 to 2
The Reference State (1) transitions to the Altered State (2) if tall, decreaser bunchgrasses, by dry weight, decreases to below 15 percent or if bare ground cover is increased beyond 20 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 T1A: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability and/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/or long-term drought leading to a decrease in rough tall bunchgrass composition to less than 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 tall, decreaser bunchgrasses are almost completely removed from the plant community and needle and thread is subdominant to short statured bunchgrasses such as Sandberg bluegrass. This transition differs from T1A in that it is generally a rapid transition and usually associated with disturbances such as repeated overgrazing or heavy human traffic. This rapid transition is generally realized where livestock are confined to small pastures for long periods of time such as horse pastures and calving lots. The driver for this transition is loss of taller bunchgrasses, which creates openings in the canopy exposing bare soil. Soil erosion results in decreased soil health, 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 water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management, long term drought, and/or heavy human disturbance.
Transition T1B
State 1 to 4
Healthy plant communities are most resistant to invasion however, regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control) and prevention 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. This will occur even if the reference community is thriving. The Rocky Mountain Foothills tend to resists invasion of cheatgrass however 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. Species composition by dry weight of invasive species approaches 10 percent.
Transition T1D
State 1 to 5
One percent canopy cover of coniferous tree/shrub cover. The trigger is the presence of seeds and/or other viable material of invasive 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, and/or revegetation. Low intensity prescribed fires to reduce competitive increaser plants such as needle and thread and Sandberg bluegrass. A low intensity fire will also reduce shrub densities. In areas with potential of annual grass infestation, fire should be carefully planned or avoided
Transition T2A
State 2 to 3
As improper grazing management continues vigor of bunchgrasses will decrease, and the shorter grasses and shrubs will increase towards the Degraded State (3). Prolonged drought will provide a competitive advantage to shrubs allowing them to become co-dominant with grasses. Shrub canopy will increase above 15 percent canopy cover. 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.
Transition T2C
State 2 to 5
One percent canopy cover of coniferous tree/shrub cover. The trigger is the presence of seeds and other viable material of invasive 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.
Restoration pathway R3A
State 3 to 2
Since the bunchgrass plant community has been significantly reduced, restoration to the Altered State (2) is unlikely unless a seed source is available. However, if a sufficient amount of grass remains on the site, chemical application and/or biological control in conjunction with proper grazing management, can reduce the amount of shrubs and invasive species and restore the site. Low intensity fire can be utilized to reduce shrubs 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 (more than 10 percent dry weight) 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. 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 T3B
State 3 to 5
One percent canopy cover of coniferous tree/shrub cover. The trigger is the presence of seeds and other viable material of invasive 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/or other viable material in the soil and management related practices that increase soil disturbance.
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 without reseeding or removal of conifer (mechanical, cultural, chemical depending on the Phase of the community). 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.
Transition T4A
State 4 to 5
One percent canopy cover of coniferous tree/shrub cover. The trigger is the presence of seeds and/or 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 following utilizing the phases established by Miller et al management and restoration methods will vary. An large majority of the conifer encroachment in MLRA 46 will fall into the early two phases of Miller's Phases.
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 and/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 this is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means 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
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 Altered State (2).
If following utilizing the phases established by Miller et al management and restoration methods will vary. An large majority of the conifer encroachment in MLRA 46 will fall into the early two phases of Miller's Phases.
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 and/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 this is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means 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
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 Degraded State (3).
If following utilizing the phases established by Miller et al management and restoration methods will vary. An large majority of the conifer encroachment in MLRA 46 will fall into the early two phases of Miller's Phases.
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 and/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 this is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means 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.
