State 1
Reference State

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

Community 1.1
Diverse grasses, shrubs, and forbs (diagnostic plant community)

Figure 5. Community 1.1 on a plateau shoulder in Colfax County, August 2018. The Ephemeral Drainageways site is visible in the background. New Mexico feathergrass is not always so dominant in this phase.

This plant community occurs on eroded soils—where productive potential and species diversity have been lost with topsoil and the seedbank it held. This community is a mix of grass, shrub, and forb species; with grasses usually being dominant. However, shrubs are much more abundant than in Community 1.2, and reach codominance at some locations. Among the grasses, warm-season species—particularly blue grama in a sod-bound state—are dominant, but cool-season grasses are at least well-represented. While one or more decreaser species (sideoats grama and/or western wheatgrass) is often present, New Mexico feathergrass is notably absent. Conversely, increaser species such as purple threeawn and ring muhly are often quite abundant. If topsoil remains, its thickness has been reduced considerably. Foliar cover is between 50 and 75 percent, and bare ground ranges from 10 to 40 percent. Total canopy cover of warm-season grasses is between 30 and 60 percent. Cool-season grass cover is typically 5 percent or less. Shrubs and forbs account for up to 35 percent and 5 percent cover, respectively. Encroaching oneseed juniper has been observed on this phase, and is especially likely where this site lies directly below the Limy Escarpments site. Annual production averages around 650 pounds per acre, but can range between 450 and 1,000 pounds per acres, depending mostly on annual weather patterns.

This community exists where season-long grazing has been practiced, thus it has experienced an increase in shrub vigor and a decrease in grass vigor. Under heavy, continuous herbivory, the depth of grass roots decreases—giving shrubs a competitive advantage in acquiring water and nutrients. As the turnover of grass roots diminishes, energy flow begins to lessen due to a decrease in soil organic matter. The loss of organic matter in situ, coupled with a loss in topsoil that occurs during transition T1A, translate to reduced water-holding capacity and nutrient availability. While prolonged grazing would have been uncommon prior to the introduction of livestock, fire was an important factor in keeping shrub species from gaining a competitive advantage and stimulating the growth of grasses.

Community 1.2
At risk: Diverse grasses, shrubs, and forbs—eroding

Figure 6. Community 1.2 on a gentle plateau riser in Colfax County, September 2017. New Mexico Feathergrass, sideoats grama, and wolfstail are all well-represented here.

This community is a mix of grass, shrub, and forb species; with grasses being dominant. However, shrubs are much more abundant than in Community 1.1, and approach codominance at some locations. Among the grasses, warm-season species are dominant, but cool-season grasses are at least well-represented. Decreasers such as New Mexico feathergrass, sideoats grama, and western wheatgrass are present, but with lesser abundance than in the reference community. Some topsoil remains, but its thickness has been reduced considerably. Foliar cover is between 55 and 80 percent, and bare ground ranges from 10 to 40 percent. Total canopy cover of warm season grasses is between 30 and 65 percent. Cool-season grass cover is typically 5 percent or less, but can range as high as 20 percent. Shrubs and forbs account for up to 25 percent and 5 percent cover, respectively. Encroaching oneseed juniper has been observed on this phase, and is especially likely where this site lies directly below the Limy Escarpments site. Annual production averages around 700 pounds per acre, but can range between 500 and 1,100 lbs/ac, depending mostly on annual weather patterns.

This community exists where season-long grazing has been practiced, thus it has experienced an increase in shrub vigor and a decrease in grass vigor. Under heavy, continuous herbivory, the depth of grass roots decreases—giving shrubs a competitive advantage in acquiring water and nutrients. As the turnover of grass roots diminishes, energy flow begins to lessen due to a decrease in soil organic matter. The loss of organic matter in situ, coupled with a loss in topsoil that occurs during pathway 1.2A, translate to reduced water-holding capacity and nutrient availability. While prolonged grazing would have been uncommon prior to the introduction of livestock, fire was an important factor in keeping shrub species from gaining a competitive advantage and stimulating the growth of grasses.

Pathway P1.1A
Community 1.1 to 1.2

Diverse grasses, shrubs, and forbs (diagnostic plant community)

At risk: Diverse grasses, shrubs, and forbs—eroding

This pathway represents a period of heavy grazing, typically season-long, which advantages the growth and reproduction of shrubs and suppresses herbaceous species that are more palatable and/or less resilient under grazing pressure. Under such a grazing regime, and in the absence of fire and/or chemical treatments, broom snakeweed and fringed sage increase in abundance and vigor. Early seral grasses such as purple threeawn and ring muhly also increase under continuous grazing. Conversely, western wheatgrass, sideoats grama, and New Mexico feathergrass will diminish unless given significant periods of rest during their growing seasons. Despite having significant gravel cover, this site is quite susceptible to erosion. As grass cover diminishes and soils are trampled during continuous grazing, soils become even more vulnerable to the effects of wind, raindrop impact, and runoff. Thus, significant amounts of soil are lost in this pathway.

Pathway P1.2A
Community 1.2 to 1.1

At risk: Diverse grasses, shrubs, and forbs—eroding

Diverse grasses, shrubs, and forbs (diagnostic plant community)

This pathway represents prescribed grazing or rest from grazing. In either case, herbaceous plants that are palatable and/or sensitive to grazing increase in vigor and abundance, and shrubs are at a competitive disadvantage.

State 2
Eroded State

Community 2.1
Sod-bound blue grama, other grasses, shrubs, and forbs—eroded

Figure 7. Community 2.1 on a fan remnant in Mora County, October 2018. Shrub dominance is rather moderate for this phase.

Figure 8. A plant community transitioning from phase 2.1 to phase 2.3 in San Miguel County, November 2017. Most of the broom snakeweed here is dead, and most of the blue grama is sod-bound.

This plant community occurs on eroded soils—where productive potential and species diversity have been lost with topsoil and the seedbank it held. This community is a mix of grass, shrub, and forb species; with grasses usually being dominant. However, shrubs are much more abundant than in Community 1.1, and reach codominance at some locations. Among the grasses, warm-season species are dominant, but cool season grasses are at least well-represented. While one or more decreaser species (sideoats grama and/or western wheatgrass) is often present, New Mexico feathergrass is notably absent. Conversely, increaser species such as purple threeawn and ring muhly are often quite abundant. If topsoil remains, its thickness has been reduced considerably. Foliar cover is between 50 and 75 percent, and bare ground ranges from 10 to 40 percent. Total canopy cover of warm season grasses is between 30 and 60 percent. Cool-season grass cover is typically 5 percent or less. Shrubs and forbs account for up to 35 percent and 5 percent cover, respectively. Encroaching oneseed juniper has been observed on this phase, and is especially likely where this site lies directly below the Limy Escarpments site. Annual production averages around 650 pounds per acre, but can range between 450 and 1,000 lbs/ac, depending mostly on annual weather patterns.

This community exists where season-long grazing has been practiced, thus it has experienced an increase in shrub vigor and a decrease in grass vigor. Under heavy, continuous herbivory, the depth of grass roots decreases—giving shrubs a competitive advantage in acquiring water and nutrients. As the turnover of grass roots diminishes, energy flow begins to lessen due to a decrease in soil organic matter. The loss of organic matter in situ, coupled with a loss in topsoil that occurs during transition T1A, translate to reduced water-holding capacity and nutrient availability. While prolonged grazing would have been uncommon prior to the introduction of livestock, fire was an important factor in keeping shrub species from gaining a competitive advantage and stimulating the growth of grasses.

Community 2.2
Blue grama, other grasses, shrubs, and forbs—eroded

Figure 9. Community 2.2 in Colfax County, September 2017. Note the cespitose habit of blue grama. While this grass species has recovered to some degree, New Mexico Feathergrass and topsoil remain absent.

This plant community occurs on eroded soils—where productive potential and species diversity have been lost with topsoil and the seedbank it held. This community is a mix of grass, shrub, and forb species; with grasses being dominant. However, shrubs are typically quite abundant. While at least one cool-season grass species generally remains, warm-season grasses—particularly blue grama with a sod-bound habit—are quite dominant. Decreasers such as sideoats grama and western wheatgrass are often low in abundance, and New Mexico feathergrass is absent. Conversely, increaser species such as purple threeawn and ring muhly are often quite abundant. The original topsoil is either gone or very thin. The most notable difference between communities 2.2 and 2.1 is that in the former, blue grama has recovered to a cespitose (bunchgrass) habit. Foliar cover is between 55 and 80 percent, and bare ground ranges from 10 to 40 percent. Total canopy cover of warm-season grasses is between 35 and 70 percent. Cool-season grass cover is typically 5 percent or less. Shrubs and forbs account for up to 20 percent and 5 percent cover, respectively. Annual production averages around 700 pounds per acre, but can range between 500 and 1,000 pounds per acre, depending mostly on annual weather patterns.

While this community has not experienced season-long grazing in a number of years, it still shows evidence of such management in the past. Most notably, topsoil is either absent or else quite thin. Thus, water-holding capacity and nutrient availability are both lower in the soils here than in State 1. Since the turnover of grass roots is the main driver of decomposition in grassland soils, this community can be expected to exhibit greater rates of nutrient cycling and accumulation of soil organic matter than community 2.1. While prolonged grazing would have been uncommon prior to the introduction of livestock, fire was an important factor in keeping shrub species from gaining a competitive advantage and stimulating the growth of grasses. Without this variable, shrubs will remain competitive.

Community 2.3
Grasses—eroded

Figure 10. Community 2.3 in Colfax County, August 2018. Blue grama is sod-bound and dominant, and shrubs are nearly absent.

Figure 11. Figure 10. Community 2.3 in San Miguel County, November 2017. This site was chemically treated 5 years prior. Note that shrubs have already re-established, and the community is transitioning to phase 2.2.

This plant community typically occurs where herbicides have recently been applied to suppress shrubs. Thus, grasses are dominant. However, species richness among grasses is no higher than in communities 2.1 and 2.2; and total species richness is quite low. While decreasers such as sideoats grama and western wheatgrass are present, their abundance is generally low, and New Mexico feathergrass is absent. Foliar cover is between 60 and 90 percent, and bare ground ranges from 5 to 30 percent. Total canopy cover of warm-season grasses is between 50 and 80 percent. Cool-season grass cover is typically 5 percent or less. Shrubs and forbs each account for less than 5 percent and 5 percent cover. Annual production averages around 800 pounds per acre, but can range between 600 and 1,000 pounds per acre, depending mostly on annual weather patterns.

Pathway P2.1A
Community 2.1 to 2.2

Sod-bound blue grama, other grasses, shrubs, and forbs—eroded

Blue grama, other grasses, shrubs, and forbs—eroded

Community Pathway: This pathway represents prescribed grazing or rest from grazing. In either case, herbaceous plants that are palatable and/or sensitive to grazing increase in vigor and abundance, and shrubs are at a competitive disadvantage. The most obvious change is that blue grama recovers from its sod-bound habit and begins to assume the habit of a bunchgrass.

Pathway P2.1B
Community 2.1 to 2.3

Sod-bound blue grama, other grasses, shrubs, and forbs—eroded

Grasses—eroded

This pathway represents the suppression of shrubs. This can result from a dry period during late summer, or from chemical treatments. Since fire requires significant biomass, this disturbance is probably quite rare in Community Phase 2.1.

Pathway P2.2A
Community 2.2 to 2.1

Blue grama, other grasses, shrubs, and forbs—eroded

Sod-bound blue grama, other grasses, shrubs, and forbs—eroded

This pathway represents a period of heavy grazing, typically season-long, which advantages the growth and reproduction of most shrubs, and suppresses herbaceous species that are more palatable and/or less resilient under grazing pressure. Blue grama responds to grazing pressure by assuming a sod-bound habit.

Pathway P2.2B
Community 2.2 to 2.3

Blue grama, other grasses, shrubs, and forbs—eroded

Grasses—eroded

This pathway represents phenomena which suppress shrubs as well as many forbs. This pathway could involve fire, chemical treatments, or a late summer drought. Since significant biomass is required to carry a fire, a period of deferred grazing is probably a necessary precursor.

Pathway P2.3A
Community 2.3 to 2.1

Grasses—eroded

Sod-bound blue grama, other grasses, shrubs, and forbs—eroded

This pathway represents a resurgence of shrubs and forbs following herbicide treatments. Concurrent season-long grazing forces blue grama into a sod-bound state and gives shrubs a competitive advantage over grasses. Additionally, shrubs enjoy a competitive advantage in the eroded, calcareous soils of State 2.

Pathway P2.3B
Community 2.3 to 2.2

Grasses—eroded

Blue grama, other grasses, shrubs, and forbs—eroded

This pathway represents a resurgence of shrubs and forbs following herbicide treatments. Concurrent prescribed grazing maintains some vigor among palatable grass species and allows blue grama to maintain a cespitose habit. However, shrubs remain at a competitive advantage in the eroded, calcareous soils of State 2.

Transition T1A
State 1 to 2

Slow variables: Continued encroachment by shrubs, coupled with the loss of herbaceous plant production, leads to decreases in total canopy cover and soil organic matter. The result is an increase in the rate of wind and water erosion—leading to the loss of topsoil and an associated decrease in available water and nutrients. Trigger event: A severe drought kills already-weakened perennial grasses, resulting in a loss in canopy cover. This, in turn, accelerates erosion. Threshold: The vigor and cover of perennial grasses is reduced to a point at which some perennial grasses die, and soil surfaces become highly susceptible to erosion.

Restoration pathway R2A
State 2 to 1

An increase in the competitive advantage of various perennial grass species through physical, chemical, and biological management practices. This restoration pathway will likely require long-term, multifaceted approaches and high-energy inputs. In order to return to State 1, erosion will have to be reversed, grazing will have to be tightly-controlled, and the re-introduction of extirpated plant species may be required. Favorable weather patterns may also be necessary.