State 1
Reference State

Community 1.1
Historic Climax Plant Community (HCPC)

Western/thickspike wheatgrasses and green needlegrass are common cool season mid grasses on this ecological site. They account for about 80% of total plant production in the HCPC. Needleandthread, another cool season mid-grass is common and tends to replace the green needlegrass when it is stressed by lack of moisture, grazing pressure, etc. About 5% of the total production is comprised of a mix of cool season short grasses and grasslike plants. These species include sandberg bluegrass, prairie junegrass, needleleaf sedge and threadleaf sedge. American vetch, a cool season nitrogen-fixing legume, is one of the most important members of the forb community. Milk vetches and prairie thermopsis are additional members of the legume family which may occur in the HCPC. Other common forbs include onion, hoods phlox, scarlet globemallow, wooly plantain, and biscuitroot. The latter group contains a mix of warm and cool season species whose relative occurrence on the site is largely influenced by the timing and amount of precipitation. Forbs contribute about 5% of the total annual production. Nuttall saltbush and winterfat are the two most important browse species occurring on the site. While Nuttall saltbush expresses itself during the cool season, winterfat is a warm season plant. Shrubs such as big sagebrush, greasewood, silver sagebrush, pricklypear cactus and fringed sagebrush may also be found in the HCPC. Shrubs normally make up about 10% of the total annual production. Broom snakeweed, annual bromes, and annual forbs are not a part of the HCPC. Their presence indicates possible ecological deterioration, or downward trend. Trend is difficult to interpret because large areas of bare ground between plants are fairly common. Total annual production averages 600 lbs/ac during normal years. However, production declines as the site regresses from the HCPC to lower successional communities. Regression may result from grazing management strategies that do not allow adequate recovery periods between grazing events, drought, and/or the disruption of the normal fire sequence. Following regression from the HCPC, soil structure appears to influence species composition. Surface layers that are vesicular, with large angular peds (blocky clods, etc) appear to limit or restrict the establishment and growth of short grasses (especially blue grama) (White and Lewis 1969). Consequently, the percentage of bare ground increases as the production of green needlegrass and western wheatgrass decline on these soils. In contrast, production of shallow-rooted and/or predominantly lateral-rooted species such as needleandthread, blue grama, sandberg bluegrass, prairie junegrass, hairy goldenaster, and hoods phlox increase when surface soils are more granular, with smaller peds, etc. The large cracks that form between the peds of the heavy soils are theorized to restrict shallow root growth and/or shear the lateral roots that have thin cortices, resulting in a reduction of the short grasses. Regardless of soil shrink/swell realities, winterfat and Nuttall saltbush may also be replaced by broom snakeweed, fringed sagewort, etc on the site. Cheatgrass and Japanese brome may invade the site. As the result of these vegetative changes, there is less litter to protect the soil and less infiltration. Hydrologic cycles are impaired when plant communities are unable to effectively use precipitation. Plant basal cover averages 15%. Litter varies from 40-50%. Consequently, bare ground may range from 35-55%. Thus, infiltration is not optimized and runoff and erosion are not minimized on the Dense Clay 10-14” p.z. ecological site. Runoff and soil erosion normally increase as the HCPC regresses to earlier seral states. The major plant species composition and production by dry weight are shown for the HCPC in the following table. Total annual production has been derived from several sources, and has been adjusted to represent a typical annual moisture cycle.

Community 1.2
Plant Community A

Range inventories conducted by NRCS on the Fort Peck and Fort Belknap Reservations indicate similarity indices of 45-64% are indicative of Community A. Non-prescribed grazing and drought reduce plant height and plant litter. Bare ground increases as the production of HCPC species decline. Surface runoff and soil temperature increases, and infiltration decreases. Production of shallow-rooted short grasses and sedges is limited by the large cracks that form between the peds as the soils dry. Pricklypear cactus is conspicuous in this community. In contrast to the HCPC, total annual production averages about 475 lbs/ac. However, western and thickspike wheatgrasses and green needlegrass still contribute 70% of the annual production. However, they are less vigorous and individual plant growth is reduced from what it is in the HCPC. Production of the short grasses and lower-successional forbs increases slightly to what it was in the HCPC. Although total shrub production did not change, production of silver sagebrush tends to replace production of winterfat and Nuttall saltbush. Plant community A is called a “pre-threshold community”. It is critical that this community be recognized and strategies implemented to prevent further regression. Although this community can improve to the HCPC through successional processes, further disturbance will result in regression to a lower state (State #2). Once Community A regresses to a lower state, normal successional processes are restricted.

Community 1.3
Plant Community B

NRCS range inventories indicate that Community B is characterized by similarity indices of 45-64%. The Community is dominated by a mix of medium and short grasses. Blue grama, threadleaf sedge, needleandthread and sandberg bluegrass increased in the community by replacing some of the mid grasses. However, western and thickspike wheatgrass and green needlegrass continued to contribute about 50% of the total annual production (average of 375 lbs/ac.). In comparison to the HCPC, sandberg bluegrass, blue grama, and other short grasses have increased. In addition, sand dropseed and tumblegrass may appear in the community. Warm season forbs increase and replace American vetch and other high-successional forbs. The warm season half-shrub, fringed sagewort, may also increase in this community. Pricklypear cactus and broom snakeweed are conspicuous. In comparison to the HCPC, litter varies from 25-35%. Bare ground increases to 50-60%. Thus, rills, flow patterns and movement of litter deposits are visible. Plant community B is called a “pre-threshold community”. It is critical that this community be recognized and strategies implemented to prevent further regression. Although this community can improve to the HCPC through successional processes, further disturbance will result in regression to a lower state (State #3). Once Community B regresses to a lower state, normal successional processes are restricted.

Pathway CP HPCP to A
Community 1.1 to 1.2

Non-prescribed grazing, drought and/or a cessation of the natural fire regime will cause regression from HCPC to Communities A. The pathway to Community A occurs on soils with vesicular, irregular, coarse granules, and blocky clods. Large cracks form between the peds (aggregates) as these soils dry. The regression to either Plant Community A may occur within a couple of years.

Pathway CP HCPC to B
Community 1.1 to 1.3

Non-prescribed grazing, drought and/or a cessation of the natural fire regime will cause regression from HCPC to Communities B. The pathway to Plant Community B occurs on soils with much smaller soil peds. Large cracks between peds are not a normal occurrence on these soils. The regression to either Plant Community A or B may occur within a couple of years.

Pathway CP A to HCPC
Community 1.2 to 1.1

The Dense Clay 10-14” p.z. site is resilient within the Reference State. Normal growing conditions, the implementation of prescribed grazing, or the re-introduction of the natural fire regime will move Plant Communities A to the HCPC. This succession can occur within a couple of years.

Pathway CP B to HCPC
Community 1.3 to 1.1

The Dense Clay 10-14” p.z. site is resilient within the Reference State. Normal growing conditions, the implementation of prescribed grazing, or the re-introduction of the natural fire regime will move Plant Communities B to the HCPC. This succession can occur within a couple of years.

State 2
Plant Community C

Community 2.1
Plant Community C

Regression of Plant Community A crosses a threshold and results in Plant Community C. This community is a steady state, which is resistant to change. It is characterized by a significant reduction in production of medium-height, cool season grasses. The amount of bare ground increases significantly. The wheatgrasses contributed about 50% of total annual growth. Individual wheatgrass plants produce few seed heads and can be low in vigor. Similarity indices during the NRCS inventories on Fort Peck and Fort Belknap (2001-2004) were less than 35% for this Community. Pricklypear cactus, broom snakeweed and annual bromes are often common in this community. Total annual production averaged 325 lbs/ac, a 20% reduction from Community A. Litter cover averages about 15%. Water flow patterns are numerous and there is moderate active pedestalling. Bare ground is moderately to much higher than expected. Compared to the HCPC, production of tall and medium height grasses has decreased, and bare ground has increased. The ecological processes of energy flow, hydrologic cycle, and nutrient cycle are disrupted.

State 3
Plant Community D

Community 3.1
Plant Community D

Regression of Plant Community B ends in Plant Community D. This community is a steady state, which is resistant to change. It is characterized by a mix of warm and cool season short grasses. Blue grama, needleandthread and sandberg bluegrass are the most common plants. Western and thickspike wheatgrasses contribute about 15% to the total annual production. Production of low-successional forbs decreased relative to Community B. Total annual production usually varies from 250-300 lbs/ac during favorable years. The NRCS inventories indicate a few winterfat and Nuttall saltbush plants persist in this community. However, dry weight production of these high-successional shrubs decreased relative to the dry weigh

Transition T1a
State 1 to 2

Plant Communities A are much less resistant to disturbance than the HCPC. Lower production, lower vegetative cover, less litter, and increased bare ground increases susceptibility to disturbance, stress etc. Extended drought and non-prescribed grazing are the most common causes of retrogression to either States 2.

Transition T1b
State 1 to 3

Plant Communities B are much less resistant to disturbance than the HCPC. Lower production, lower vegetative cover, less litter, and increased bare ground increases susceptibility to disturbance, stress etc. Extended drought and non-prescribed grazing are the most common causes of retrogression to either States 3.

Restoration pathway R2a
State 2 to 1

Plant community C is resistant to significant succession. The adverse soil conditions and a theorized inadequate seed bank of high successional species greatly restrict potential for succession to State #1. Although succession usually does not occur within a reasonable length of time, anecdotal evidence indicates succession may occur with the combination of prescribed grazing, the resumption of a normal fire regime, and an extended period of favorable precipitation. Favorable environmental factors may favor succession of Plant Communities C to Plant Communities A. These possibilities are depicted by dashed arrows in the state and transition diagram. In comparison to “normal” ecological sites (Silty 10-14” p.z., Clayey 10-14” p.z. and Sandy 10-14” p.z.) having soils > 20 inches in depth, the average annual aboveground production on this Dense Clay 10-14” p.z. ecological site is 50-60% less. Mechanical treatments and range seeding are not recommended on this site.

Restoration pathway R3a - D to B
State 3 to 1

Plant community D is resistant to significant succession. The adverse soil conditions and a theorized inadequate seed bank of high successional species greatly restrict potential for succession to State 1. Although succession usually does not occur within a reasonable length of time, anecdotal evidence indicates succession may occur with the combination of prescribed grazing, the resumption of a normal fire regime, and an extended period of favorable precipitation. Favorable environmental factors may favor succession of Plant Community D to Plant Community B. These possibilities are depicted by dashed arrows in the state and transition diagram. In comparison to “normal” ecological sites (Silty 10-14” p.z., Clayey 10-14” p.z. and Sandy 10-14” p.z.) having soils > 20 inches in depth, the average annual aboveground production on this Dense Clay 10-14” p.z. ecological site is 50-60% less. Mechanical treatments and range seeding are not recommended on this site.