Ecological dynamics
This ecological site developed through time under the influence of climate, geologic parent materials, fire, plants and animals. Research consistently shows that precipitation is the principal factor altering productivity on ecological sites in the Northern Great Plains (Heitschmidt et al. 2005). The same authors concluded that grazing reduces herbage standing crop, whereas its effects on above ground net primary production varies with timing of grazing and precipitation events, along with the functional and structural composition of the plant community.
It is believed that, prior to the arrival of European man, fire occurred on 5-7 year interval (Frost 1998). These fires were ignited by lightning and by early man in his attempts to manipulate the environment. Clearly, the current role of fire on the Glaciated Plains is much reduced from its historical importance.
Plant community interpretations are based on the Historic Climax Plant Community (HCPC). The HCPC was determined by evaluating rangeland relic areas, and other areas protected from excessive disturbance. The HCPC is comprised of a mixture of cool and warm season perennial grasses, forbs and shrubs. About 85% of the annual production is from grasses and grasslike plants, most of which is produced during the cool season. Forbs and shrubs contribute 10% and 5%, respectively, to total annual production. Total annual production averages 1600 lbs/ac during normal years.
This site is moderately resistant and resilient to disturbances. Departures from the HCPC generally result from management actions, drought, a change in the natural fire regime, colonization and recruitment of noxious weeds, etc.. As the HCPC regresses to lower seral stages, the deep-rooted perennial grasses such as little bluestem and prairie sandreed are replaced by blue grama, sandberg bluegrass, fringed sagewort, scurfpeas, threadleaf sedge, hairy goldaster, green sagewort, and many flowered aster. In early seral stages, the dominance of these short grasses, warm season forbs and half-shrubs in the plant community disrupts ecological processes, impairs the biotic integrity of the site, and adversely affects resiliency. The site becomes more susceptible to erosion. The system’s ability to recover to higher seral states is restricted or impeded.
Successional pathways of the Sandy 10-14” p.z. ecological site cannot be satisfactorily described using traditional theories of plant succession leading to a single climax community (Briske et al. 2005). This ecological site is more aptly described using state-and-transition vegetation dynamics in a non-linear framework. A “state” is an alternative, persistent vegetation community that is not simply reversible in the linear successional framework. States are depicted as seral stages, while pathways between states are “transitions.” As the HCPC regresses to an early seral state, it is theorized that a threshold is crossed somewhere within the mid seral state. Plant communities occurring below this threshold are in a steady state. Transitions may be triggered by climatic events, fire, grazing, farming, burning, etc.
Three important plant communities and the successional pathways within the Reference State (State 1) are shown in the following diagram. In addition, transitions from Community B (State 1) to State 2 (Community C) and State 3 (Community D) are also illustrated. The diagram also depicts a third transition from State 1 (Reference State) to State 4. Ecological processes are discussed in the plant community descriptions, which follow the diagram.
Community 1.1
Decreaser dominant
Tall- and medium-height cool- and warm-season perennial grasses, about ten percent perennial native forbs; about 5 percent native shrubs; total annual production is 1600 pounds per acre.
The interpretive plant community for this site is the Historic Climax Plant Community (HCPC). Cool season tall and mid-grasses (such as prairie sandreed grass, western wheatgrass, Indian ricegrass, bluebunch wheatgrass, and needle and thread grass) dominate the HCPC. These native, perennial grasses represent about 80% of the total annual plant production in the community. Little bluestem is uncommon on this site. Bluebunch wheatgrass is the dominant grass on this site.
Less common species in the HCPC include plains muhly, prairie junegrass, threadleaf sedge, plains reedgrass, sandberg bluegrass and blue grama. Dotted gayfeather, and purple and white prairie clovers are important warm season forbs. American vetch may be the most common cool season forb. The group of inconspicuous forbs that should be present in small amounts include scarlet globemallow, penstemon, many-flowered aster, erigeron, scurfpeas, and hairy goldenaster. Total forb production normally represents about 10% of the total annual production.
Silver sagebrush, yucca, prairie rose and western snowberry may occur in the HCPC. Overall, shrubs account for about 5% of the annual plant production.
Range inventory data collected (in 2001 and 2004) on the Fort Peck and Fort Belknap Indian Reservations indicate total above ground production varies from 1,270 to 2,550 lbs/ac. The latter inventory was conducted during a favorable precipitation period, which probably explains why the production is slightly higher than the 1600 lbs/ac which is normally expected on this site. Average annual production is expected to be slightly higher and lower than 1600 lbs/ac, respectively on more mesic and xeric portions of the Glaciated plains. During the inventories on the Reservations, similarity indices (SI) >75% were recorded within the HCPC.
This plant community is well adapted to the glaciated plains. Precipitation is the most important factor influencing production. The functional and structural diversity of plant species (perennials (with a few annuals and biennials), cool and warm season grasses, forbs and shrubs) optimize the capture of solar energy and maximize subsequent plant growth through the efficient use of available soil water and nutrient cycling. Following a disturbance which reduces the competitiveness of the species at HCPC, the taller, warm and cool season grasses (Indian ricegrass, bluebunch wheatgrass, western/thickspike wheatgrass) decrease. They are replaced by shorter height species such as needle and thread, blue grama, sand dropseed, and fringed sagewort. With further disturbance, annual bromes, wooly plantain, fluffgrass, and red threeawn become conspicuous. With proper grazing management and non-drought conditions, the HCPC species will replace these lower successional species within a few years.
Basal plant cover averages 35%. Litter is in contact with about 60% of the soil surface. Less than 5% of the soil surface should be bare, or unprotected by litter, rock, moss, and plant canopy. Bare ground should be less than 2 inches in diameter. Rills should not be present and water flow patterns should be barely observable.
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 precipitation cycle.
Table 6. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Grass/Grasslike |
942 |
1547 |
1961 |
| Forb |
123 |
157 |
168 |
| Shrub/Vine |
56 |
90 |
112 |
| Total |
1121 |
1794 |
2241 |
Table 7. Ground cover
| Tree foliar cover |
0%
|
| Shrub/vine/liana foliar cover |
0%
|
| Grass/grasslike foliar cover |
0%
|
| Forb foliar cover |
0%
|
| Non-vascular plants |
0-5%
|
| Biological crusts |
0-2%
|
| Litter |
40-60%
|
| Surface fragments >0.25" and <=3" |
0-3%
|
| Surface fragments >3" |
0-1%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0-1%
|
Table 8. Soil surface cover
| Tree basal cover |
0%
|
| Shrub/vine/liana basal cover |
1-2%
|
| Grass/grasslike basal cover |
25-30%
|
| Forb basal cover |
1-5%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
0%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0%
|
Table 9. Canopy structure (% cover)
| Height Above Ground (m) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.15 |
– |
0-20% |
0-10% |
0-40% |
| >0.15 <= 0.3 |
– |
0-40% |
0-30% |
0-50% |
| >0.3 <= 0.6 |
– |
0-30% |
0-40% |
0-8% |
| >0.6 <= 1.4 |
– |
0-10% |
0-20% |
0-2% |
| >1.4 <= 4 |
– |
– |
– |
– |
| >4 <= 12 |
– |
– |
– |
– |
| >12 <= 24 |
– |
– |
– |
– |
| >24 <= 37 |
– |
– |
– |
– |
| >37 |
– |
– |
– |
– |
Community 1.2
Increaser co-dominant
Lower production; shift in species composition; medium- and tall-height cool- and warm-season perennial grasses; about ten percent native forbs and five percent native shrubs.
Total plant production averages about 1200 lbs/ac in this Plant Community, or 75% of the production at the HCPC. Production of the tall, cool and warm season perennial bunchgrasses (green needlegrass, and bluebunch wheatgrass) decreased from the HCPC. In contrast, production of the medium height rhizomatous western/thickspike wheatgrasses and the lower-successional needle and thread grass increased. In comparison to the HCPC, the relative production of short height grasses and sedges such as blue grama, prairie junegrass, plains reedgrass and threadleaf sedge increased to about 20% of the total plant production. Sand dropseed may show up in some communities. Exact response by these species varies with the kind of disturbance (drought, grazing, etc.) and with precipitation (amount and timing).
Native forb production continues to account for about 10% of the total production. However, scurfpeas and hairy goldenaster increase at the expense of the prairie clovers and American vetch. Shrubs account for less than 10% of the total production. However, the half-shrub fringed sagewort often increases. These increases following disturbance are due to enhanced growth of established plants and seedling recruitment. Not only do individual plants that survive the disturbance grow bigger and produce more seed, but seed is dispersed beginning in summer and continued through the winter (Bai and Romo 1997). SI indices from 55-75% are associated with this community. Litter cover decreases to 50% and bare ground increases to 5-10%. In contrast to the HCPC, range conservationists have slight to moderate concerns regarding plant functional/structural group shifts, decreasing amount of litter, and increased presence of lower successional plants.
Community 1.3
Increaser dominant, at risk
Medium- and short-height cool-season perennial grasses; increase of lower-successional forbs; increase of lower-successional shrubs; some invasive plants present; more bare ground, and less litter; total annual production is 800 pounds per acre.
Plant Community B is dominated by a mix of cool and warm season perennial grasses such as needle and thread, western/thickspike wheatgrass, blue grama, plains reedgrass, prairie junegrass and upland sedges. Only a few individual plants of bluebunch wheatgrass, green needlegrass and little bluestem remain in the Community. The short grass and grasslike plants make up more than 30% of the total production. Total vegetative production declines to about 900 lbs/ac in a normal year.
Hairy goldenaster, scarlet globemallow, scurfpeas and other warm season forbs increase at the expense of the prairie clovers and American vetch. Green sagewort and fringed sagewort, a half-shrub, increases at the expense of winterfat and other desirable forage species. Forbs and shrubs, respectively account for more than 10% and 5% of the total plant production. SI indices for this community vary from 45-55%.
Plant basal cover varies from 20-25%. Litter provides cover for about 35-40% of the ground, while bare ground increases to 10-15%. An examination of the soil surface suggests that there is inadequate regeneration of desired species, inadequate vigor of key species, and possible increases in amount of bare ground.
Plant Community B is fairly resilient, but it is not highly resistant to disturbance. It is the “pre-threshold” community. Therefore, it is critical that this community be recognized and strategies implemented to prevent further regression. Community B can readily regress to a lower state, from which succession back to the HCPC community or Plant Community A would be restricted.
Pathway 1.1a
Community 1.1 to 1.2
Non-prescribed grazing, drought (3 to 5 years), and no fire
Successional pathways from the HCPC are influenced by frequency, timing and intensity of grazing, amount and timing of precipitation, fire, insect infestations, colonization and recruitment of noxious weeds, etc. As communities regress from HCPC, short warm and cool season grasses increase at the expense of mid and tall cool season grasses.
Pathway 1.1b
Community 1.1 to 1.3
Extended drought (greater than 7 years), non-prescribed grazing, no fire
Pathway 1.2a
Community 1.2 to 1.1
Prescribed grazing, fire, normal or favorable precipitation
Plant Community A is resilient. Successional processes can return Plant Community A to the HCPC. The process is facilitated by prescribed grazing, the incorporation of the natural fire regime into the system, and by normal precipitation.
Pathway 1.2b
Community 1.2 to 1.3
Prolonged drought (5 to 7 years), non-prescribed grazing, no fire
Prolonged drought, non-prescribed grazing, and the continued absence of fire in the system causes retrogression to Community B. The effects of drought and poor grazing management are readily apparent with careful observation.
Pathway 1.3a
Community 1.3 to 1.2
Fire, prescribed grazing, favorable precipitation
Favorable precipitation, prescribed grazing and a normal fire regime are normally required for succession to higher communities (HCPC and/or Plant Community A). Management strategies should focus on proper utilization and grazing deferment to increase vigor and seed production of desirable plants, and to increase litter cover.
Community 2.1
Clubmoss short-grass
Clubmoss; warm- and cool-season short-height perennial grasses; total annual production less than 500 pounds per acre; invasive species present.
Community C occurs on this site when there is an argillic horizon present.
Clubmoss, blue grama, prairie junegrass, sandberg bluegrass, and other short grasses dominate this community. Although some western wheatgrass persists as single shoots with few seed stalks, it is difficult to find green needlegrass, little bluestem and bluebunch wheatgrass. Japanese brome and cheatgrass often occur in this community.
Wooly plantain, hoods phlox, hairy goldenaster and western yarrow are common forbs. Fringed sagewort (a half-shrub) usually increases while the shrubs decrease in abundance. Total vegetative production averages about 550 lbs/ac.
Dense clubmoss was present at 50% of the data collection plots located on the Sandy Site during the range inventories on the Fort Peck and Belknap Reservations in 2001-2004. In some cases, it formed a mat-like carpet with 20-70% ground Cover. The presence of clubmoss on these sites is indicative of an argillic horizon. There are very few seedlings of desirable species emerging through the clubmoss. Some researchers hypothesize that this is due to an inadequate seedbank (Romo and Bai 2004). SI indices of less than 25% are associated with Community C.
Soil erosion is normally not a serious problem because of the cover provided by clubmoss. However, NRCS specialists often reported that they were concerned about inadequate litter, slight surface erosion by water, and noxious plants. The clubmoss disrupts the hydrologic cycle (capture, storage and redistribution of precipitation) by impeding infiltration and percolation. Less vegetative growth is available for transfer to litter, and nutrient cycling is delayed or impeded.
In comparison to the State 1 communities, State 2 is less efficient in capturing solar energy and converting it to carbohydrates for plant growth. The absence of tall and mid cool season perennial grasses, plus the shift from cool season plants to warm season plants, indicates that the structural and functional processes of the site have been disrupted.
Community 3.1
Short-grass dominant
Short-height, warm- and cool-season perennial grasses; lower-successional forbs; more than five percent native shrubs; invasive species more prevalent; more bare ground.
Plant Community D occurs on soils that do not have an argillic horizon. This Community is dominated by blue grama, prairie junegrass, sandberg bluegrass, threadleaf sedge, and other short grasses and grass-like plants. Western wheatgrass and needle and thread are minor components of the community.
Clubmoss is present on many sites, but is much less dominant than in State 2. Hoods phlox, wooly plantain, hairy goldenaster, cudweed sagewort, and scarlet globemallow are common forbs. Fringed sagewort is a common half-shrub. Broom snakeweed and prickly pear cactus increase in response to the more xeric environment (less plant cover, less litter, more evaporative losses, lower humidity, etc.). Total vegetative production averages about 650 lbs/ac. SI indices of 15-35% are associated with this community.
In contrast to communities in State 1, range conservationists express moderate to extreme concerns about plant community composition, functional/structural groups, litter, annual production, and invasive plants. Each of the primary processes: 1) hydrology (the capture, storage and redistribution of precipitation), 2) energy capture (conversion of sunlight to plant and animal matter), and 3) nutrient cycling (the cycle of nutrients through the physical and biotic components of the environment) has been degraded beyond the point of self-repair within a reasonable length of time and without external inputs of energy. For example, when tall, high producing, perennial grasses are replaced by short grasses (blue grama, clubmoss and prairie junegrass), the abilities of the plant community to maximize the conversion of solar energy to plant biomass and efficiently utilize available precipitation are impaired. Less solar energy is captured and converted to plant carbohydrates. Plant productivity declines, and there are fewer plants and less litter to protect the soil. As bare ground increases, infiltration decreases and/or surface runoff and soil evaporation increases. Because ecological processes of the site are no longer balanced and sustained, shallow rooted, warm season species continue to gain a competitive advantage over the tall, deep rooted, perennial species. The biotic integrity of the site is degraded. Thus, the regression from Community B to either State 2 or State 3 crosses a threshold. Thresholds are defined as a point in space and time at which one or more of the primary ecological processes responsible for maintaining the sustained equilibrium of the state degrades beyond the point of self-repair.
Community 4.1
Go Back Land
Seeded to mostly introduced species.
More than a million acres of former cropland in the Glaciated Plains are seeded to introduced and native species. These seedings resulted from Society’s concerns regarding land stewardship and erosion, and have been largely funded by the Federal Government. The government programs have spanned from the 1940’s (Bankhead Jones Act) to the present (Conservation Reserve Program-CRP).
Crested wheatgrass was the primary species seeded under the direction of the Bankhead Jones Act. Crested wheatgrass, intermediate and pubescent wheatgrasses, smooth bromegrass, and some native grasses were seeded during the Soil Bank Programs of the 1960-1970 era. Both introduced and native species were seeded during the CRP program (1985-present). There are over 220,000 acres of CRP in Valley County alone.
The future of these “go back lands” is not predicted in the state and transition model. Depending on government programs and agricultural prices, these lands could stay in permanent vegetation with limited haying and grazing, be fully used as pasture for grazing livestock, or be converted to cropland.
Transition T1A
State 1 to 2
Extended drought (greater than 7 years), non-prescribed grazing, no fire
Any combination of extended drought, non-prescribed grazing and unfavorable climatic patterns can cause regression from Plant Community B to lower States. Soil scientists have observed that the presence of an argillic horizon in the soil will normally result in State 2. When soils do not have an argillic horizon, regression usually leads to State 3. These relationships may not occur in all communities or locations (Van Dyne and Vogel 1967).
Context dependence. When soils have an argillic horizon
Transition T1B
State 1 to 3
Extended drought (greater than 7 years), non-prescribed grazing, no fire
Any combination of extended drought, non-prescribed grazing and unfavorable climatic patterns can cause regression from Plant Community B to lower States. Soil scientists have observed that the presence of an argillic horizon in the soil will normally result in State 2. When soils do not have an argillic horizon, regression usually leads to State 3. These relationships may not occur in all communities or locations (Van Dyne and Vogel 1967).
Context dependence. When soils do not have an argillic horizon
Transition T1C
State 1 to 4
Cultivated, Seeding
Restoration pathway R2A
State 2 to 1
Mechanical treatment (see NRCS Job sheet 548), Seeding, or mechanical treatment, prescribed grazing with precipitation.
The implementation of prescribed grazing, re-implementation of the natural fire regime and a favorable precipitation pattern normally will not induce succession from States 2 and 3. Succession from these States back to State 1 usually requires a significant input of energy.
Mechanical treatments are often used to induce and facilitate succession on this ecological site. Mechanical treatments should not be used on slopes greater than 10% (See NRCS Conservation Practice 548). Although seeding normally is not recommended following a mechanical treatment, the absence of key species may make it necessary to seed following treatment in State 2. Because wind erosion is a concern, a long-term comprehensive management plan is essential to the successful management of these states. Without adequate grazing deferment following treatment and a prescribed grazing plan, the desired effects of mechanical treatment will not be achieved. Failure to follow a comprehensive plan may result in economic losses (Kulshreshtha et al 2002). Although Kulshreshtha et al concluded that mechanical treatments were not economically feasible in Saskatchewan, experience along Montana’s Highline suggests otherwise. With prescribed grazing and plant succession, the effective life of treatment should be greater than 10 years (life expectancy used by researchers).
Range seeding is usually not necessary following mechanical treatment of State 3. The number of desired plants (and seed) is usually adequate to facilitate succession.
The necessity of proper management should not be overlooked on this productive ecological site. Research has documented succession occurring, during favorable precipitation cycles, in many Northern Great Plains plant communities. Experience indicates that fire (if there is adequate fuel) reduces clubmoss cover. At locations where the surface soil is intact and has not been adversely impacted by erosion, prolonged favorable climatic conditions combined with proper management may induce succession from Plant Communities C and D across the threshold (to State 1). It is theorized that the significant input of energy that is normally required to move succession across a threshold may not be needed.
Restoration pathway R3A
State 3 to 1
Prescribed grazing with favorable precipitation, fire
The implementation of prescribed grazing, re-implementation of the natural fire regime and a favorable precipitation pattern normally will not induce succession from States 2 and 3. Succession from these States back to State 1 usually requires a significant input of energy.
Mechanical treatments are often used to induce and facilitate succession on this ecological site. Mechanical treatments should not be used on slopes greater than 10% (See NRCS Conservation Practice 548). Although seeding normally is not recommended following a mechanical treatment, the absence of key species may make it necessary to seed following treatment in State 2. Because wind erosion is a concern, a long-term comprehensive management plan is essential to the successful management of these states. Without adequate grazing deferment following treatment and a prescribed grazing plan, the desired effects of mechanical treatment will not be achieved. Failure to follow a comprehensive plan may result in economic losses (Kulshreshtha et al 2002). Although Kulshreshtha et al concluded that mechanical treatments were not economically feasible in Saskatchewan, experience along Montana’s Highline suggests otherwise. With prescribed grazing and plant succession, the effective life of treatment should be greater than 10 years (life expectancy used by researchers).
Range seeding is usually not necessary following mechanical treatment of State 3. The number of desired plants (and seed) is usually adequate to facilitate succession.
The necessity of proper management should not be overlooked on this productive ecological site. Research has documented succession occurring, during favorable precipitation cycles, in many Northern Great Plains plant communities. Experience indicates that fire (if there is adequate fuel) reduces clubmoss cover. At locations where the surface soil is intact and has not been adversely impacted by erosion, prolonged favorable climatic conditions combined with proper management may induce succession from Plant Communities C and D across the threshold (to State 1). It is theorized that the significant input of energy that is normally required to move succession across a threshold may not be needed.
