State 1
Reference State

Community 1.1
Historic Climax Plant Community (HCPC) Mid and tall cool-season perennial grasses, cool and warm-season perennial grasses, 5 percent native forbs, and 10 percent native shrubs.

Mid and tall cool-season perennial grasses, cool and warm-season perennial grasses, 5 percent native forbs, and 10 percent native shrubs. Western/thickspike wheatgrass, bluebunch wheatgrass and green needlegrass are common cool season mid grasses on this ecological site. Alkali sacaton, a tall warm season grass occurs on this site in the eastern glaciated plains. These high-successional grasses account for about 75% of total plant production in the HCPC. Needle and thread, another cool season mid grass is common and tends to replace the green needlegrass when it is stressed by lack of moisture, grazing or etc. About 10% of the total production is comprised of a mix of warm and cool season short grasses and grasslike plants. These species include: blue grama, sandberg bluegrass, plains reedgrass, 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. White and purple prairie clover are important warm season legumes. Additional nitrogen is fixed by lower successional legumes (milkvetches, scurfpeas, and prairie thermopsis). Onion, hoods phlox, scarlet globemallow, wooly plantain, and biscuitroot often occur in the HCPC. 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, greasewood and silver sagebrush are the most important browse species occurring on this site. While the former two species make their major growth and flower during the cool season, silver sagebrush is a warm season species. Shrubs such as big sagebrush and pricklypear cactus may occur in some areas. Fringed sagebrush, a half-shrub 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 within the HCPC averages 900 lbs/ac during normal years. Thus production is 300 lbs/ac higher than it is on the Dense Clay 10-14” p.z. ecological site, and 400 lbs/ac less than on the Clayey 10-14” p.z. ecological site. Production declines as the HCPC 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. The above disturbances favor the replacement of green needlegrass, bluebunch wheatgrass, and western/thickspike wheatgrass by needle and thread, blue grama, sandberg bluegrass, prairie junegrass, hairy goldenaster, and hoods phlox. Nuttall saltbush may also be replaced by broom snakeweed, fringed sagewort, etc. 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 varies from 7-20%. Litter varies from 40-50%, and bare ground ranges from 25-45%. Thus, surface runoff and erosion are potential concerns on the Clay Pan 10-14” p.z. ecological site. Runoff and soil erosion 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 Reduced production, mid and tall cool-season perennial grasses, cool- and warm-season short grasses, 5 percent forbs and 10 percent shrubs.

Reduced production, mid and tall cool-season perennial grasses, cool- and warm-season short grasses, 5 percent forbs and 10 percent shrubs. Total annual production is about 80% of the HCPC. Western and thickspike wheatgrasses, and green needlegrass still contribute approximately 60% of the annual production. However, they are less vigorous and individual plant growth is reduced from what it is in the HCPC. The short grass production increases in comparison to the HCPC. Plant height and plant litter are reduced while bare ground increases. Surface runoff and soil temperature increases, infiltration decreases, and shallow-rooted short grasses and sedges gain a competitive advantage over medium height, deep-rooted cool season perennial grasses. They are able to compete more successfully with the mid-grasses because of the ability of relatively shallow root systems to utilize shallowly penetrating moisture, characteristic of this site. Total shrub production continues to represent about 5% of total annual production. However, vigor of the prairie clovers and American vetch has decreased relative to the vigor of hoods phlox and other low-successional forbs. Total shrub production remains at about 10% of the total annual production.

Community 1.3
Plant Community B - Pre-threshold Community Lower production, mid cool-season perennial grasses, short cool and warm-season perennial grasses, increase of lower successional forbs and half-shrubs.

Lower production, mid cool-season perennial grasses, short cool and warm-season perennial grasses, increase of lower successional forbs and half-shrubs. This Community is dominated by a mix of medium and short grasses. Blue grama, threadleaf sedge, needle and thread and sandberg bluegrass increased in the community by replacing some of the mid grasses. However, western and thickspike wheatgrass and green needlegrass continue to contribute nearly 50% of the total annual production. In comparison to Community A, the short grasses contain more blue grama, a warm season species. Sand dropseed and tumblegrass may also begin to appear in the community. Warm season forbs increase and replace American vetch and other high-successional forbs. The warm season half-shrub, fringed sagewort, increases in production. Pricklypear cactus and broom snakeweed are conspicuous in this community. Annual production is 40-60% of potential for the site. Plant species in this community tend to exhibit more salt tolerant characteristics than the species found in the HCPC or Community A. Infiltration is moderately reduced due to adverse changes in plant community composition and/or distribution. The amount of bare ground is moderately higher than expected for this site (bare ground = 45-60%). In comparison to the HCPC, total plant cover varies from 30-40%. Litter is reduced to 10-15%, which is moderately less, relative to site potential and weather. Active rill formation is slight at infrequent intervals, mostly in exposed areas. Water flow patterns match what is expected for the site, erosion is minor with some instability and deposition (USDI and USDA 2000). Plant community B is called the “pre-threshold community”. It is critical that this community be recognized and strategies implemented to prevent further regression. Although this community can improve to either Community A or HCPC through successional processes, further disturbance will result in regression to a lower state. Once Community B regresses to a lower state, normal successional processes are restricted.

Pathway 1.1A
Community 1.1 to 1.2

No fire, non-prescribed grazing, drought (3 to 5 years) Non-prescribed grazing, drought and/or a cessation of the natural fire regime will cause regression from HCPC to Community A.

Pathway 1.2A
Community 1.2 to 1.1

Fire (natural interval 10 to 12 years), prescribed grazing Favorable growing conditions, the implementation of prescribed grazing, or periodic fire will move Plant Community A to the HCPC. This succession can occur within a couple of years.

Pathway 1.2B
Community 1.2 to 1.3

No fire, non-prescribed grazing, prolonged drought (5 to 7 years) Community A will regress to Community B under non-prescribed grazing, prolonged drought, or an extended period without fire. The rate of regression varies with the kind, intensity, frequency, and duration of the disturbances. Severe drought may cause retrogression within a couple years.

Pathway 1.3A
Community 1.3 to 1.2

Fire, prescribed grazing, favorable precipitation The Clay Pan 10-14” p.z. ecological site is resilient within the Reference State. Prescribed grazing and/or a period of favorable precipitation will induce succession from Community B to Community A within a reasonable time frame.

State 2
Degraded State

Community 2.1
Plant Community C Short cool- and warm-season perennial grasses, half-shrubs and lower successional forbs, medium-height cool-season grasses, cactus and annual species present, increased bare ground, and decreased total annual production

Short cool- and warm-season perennial grasses, half-shrubs and lower successional forbs, medium-height cool-season grasses, cactus and annual species present, increased bare ground, and decreased total annual production Plant Community C is characterized by a significant reduction in species composition by weight of medium-height, cool season grasses. Wheatgrasses contribute about 25% of total annual growth. Plants produce few seed heads and are low in vigor. This community is dominated by low-successional grasses and sedges. Blue grama, prairie junegrass, other short grasses, sedges and clubmoss contribute about 50% of the total annual production. Clubmoss cover is usually most severe on soils with loamy A and E horizons. Broom snakeweed, fringed sagewort and pricklypear cactus are conspicuous in the community. Japanese brome, cheatgrass, annual forbs (fanweed and pepperweed), and curlycup gumweed will be present. Total annual production is reduced about 75% from levels in the HCPC. Percent composition of forbs and shrubs are highly variable from place to place and from year to year in this community. Variability is apparent in productivity and occurrence of individual species. Litter cover averages about 10%, which is a large reduction relative to site potential. Water flow patterns are numerous and there is moderate active pedestalling. In communities that are not characterized with clubmoss, bare ground is moderately to much higher than expected. There is moderate soil loss or degradation in interspaces with some degradation beneath plant canopies. Compared to the HCPC, there has been a structural shift from medium height to short grasses, and a functional shift from cool to warm season plants. Reproductive capability of cool season plants is greatly reduced relative to recent climatic conditions.

Transition T1A
State 1 to 2

Non-prescribed grazing, no fire, extended drought (greater than 7 years) However, Community B is much less resistant to perturbations than Community A. Lower production, lower vegetative cover, less litter, and increased bare ground contribute to increase Community B’s susceptibility to disturbance. Extended drought and non-prescribed grazing can lead to further retrogression (State 2). The threshold separating Communities B and C appears to be the functional threshold, below which the type, amount, and pattern of vegetation is often inadequate to prevent accelerated soil erosion.

Restoration pathway R2A
State 2 to 1

Prescribed grazing, fire (natural interval 10 to 12 years), prolonged favorable precipitation. Plant community C is a steady state. It is resistant to significant succession. Blue grama, other short grasses, sedges and clubmoss form a competitive community. The adverse soil conditions and a theorized inadequate seed bank of species found in State #1 greatly restrict potential for succession to State #1. When clubmoss cover is more than 20-25%, succession is not expected to occur within a reasonable length of time. However, significant succession may occur with the combination of prescribed grazing, implementation of the natural fire regime, and an extended period of favorable moisture. This potential is depicted with the dashed line in the state and transition diagram. In comparison to more common ecological sites with moderately deep to deep soils (ie, Silty 10-14” p.z., Clayey 10-14” p.z., and Sandy 10-14” p.z.), annual production on a Clay Pan 10-14” p.z. ecological site is about 30% less. Therefore, vegetation response to mechanical treatments and range seeding will be less than the response expected on the higher producing sites (NRCS Conservation Practice Standard 548-1).