Ecological dynamics
This ecological site developed through time under the influence of climate, geological parent material, 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 theorized that these lands burned on a natural interval of 5-7 years (Frost 1998). Fires were ignited by lightning and by Early Americans who were attempting to manipulate the environment.
The resultant historic climax plant community (HCPC) is the basis for plant community interpretations. 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 grasses, forbs and shrubs. About 85% of the annual production is from grasses and sedges, most of which is produced during the cool season. Forbs and shrubs contribute 10% and 5%, respectively, to total annual production. Total vegetative production averages 1600 lbs/ac during normal years.
This site is resistant and resilient to disturbance. Departures in the HCPC are brought about by management actions, drought, a change in the natural fire regime, colonization and recruitment of noxious weeds, etc. The integrity of the site can be readily damaged with the continued absence of prescribed grazing and during prolonged drought. As the HCPC regresses to lower seral stages, the deep-rooted perennial grasses are replaced by blue grama, sandberg bluegrass, fringed sagewort, hoods phlox, threadleaf sedge, hairy goldenaster, and dense clubmoss. The dominance of these “lower-successional” species in the plant community disrupts ecological processes, impairs the biotic integrity of the site, and restricts the system’s ability to recover to higher seral states. The potential of succession back to the HCPC varies with the interaction of all environmental factors.
State and Transition Diagram
Trends in plant community dynamics, states, transitional pathways and thresholds have been evaluated and determined through experience and research. Successional pathways of the Silty 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). 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. Succession back to the HCPC does not occur within a reasonable length of time, and/or without a large input of energy.
Three plant communities and the successional and regressional pathways that commonly occur within the Reference State (State #1) are shown in the following diagram. In addition, the transitions from Plant Community B (State #1) to State #2 (Plant Community C) and State #3 (Plant Community D) are also illustrated. A third transition denotes the pathway from State #1 to an introduced perennial grass seeding (State #4). Ecological processes are discussed in the plant community descriptions, which follow the diagram.
Community 1.1
Historic Climax Plant Community (HCPC)
Tall and medium-height cool-season perennial grasses, about 10 percent perennial native forbs, about 5 percent native shrubs, bare ground equals 0 to trace
Tall and medium-height cool-season perennial grasses, about 10 percent perennial native forbs, about 5 percent native shrubs, total annual production @ 1600 lbs/ac, bare ground equals 0 to trace.
The interpretive plant community for this site is the Historic Climax Plant Community (HCPC). Cool season tall and mid-grasses (such as green needlegrass, western wheatgrass, thickspike wheatgrass, porcupine grass and needle- and thread grass) dominate the HCPC. These cool season grasses represent about 75% of the total annual plant production in the community. Bluebunch wheatgrass is often the dominant species on the Silty 10-14” p.z. site in the central Glaciated Plains. Bluebunch wheatgrass becomes increasingly scarce on this site as one moves east of Hinsdale, MT, while little bluestem becomes increasingly scarce as one moves west.
Prairie junegrass, upland sedges and plains reedgrass (cool season species) and blue grama (a warm season species) also occur in the HCPC. Dotted gayfeather, scurfpeas, prairie clovers and other forbs make up less than 10% of the annual production. American vetch, groundplum milkvetch, purple and white prairie clover and scurfpea are important because of their ecological role in the nitrogen cycle.
Winterfat is the most prevalent shrub and is also a valuable forage plant for wildlife and livestock forage, but it seldom produces more than 80 lbs/ac in any community. Silver sagebrush and western snowberry commonly occur in the lower landscape positions of this site. They have some value for wildlife but tend to be restricted to lower landscapes that may benefit from rare flooding and livestock forage. 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 scheduling of the inventories coincided with favorable precipitation cycles. Therefore, it is recommended that Thus, total annual production averages 1600 lbs/ac during normal years. Production varies from 1100 lbs/ac in unfavorable years to 2000 lbs/ac during favorable years. Average annual production is expected to increase and decrease, respectively on more mesic and xeric portions of the Glaciated plains. Similarity indices (SI) greater than 75% were recorded within the HCPC.
This plant community is well adapted to the glaciated plains. Precipitation is the most important factor influencing production (Heitschmidt et al 2005). The functional and structural diversity of plant species (annuals, perennials, 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 prolonged disturbance which reduces the competitiveness of tall bunchgrasses, production of rhizomatous mid-grasses and short grasses increase. When disturbances are sustained for a prolonged period, woolly plantain, annual bromes or other annual species may invade a community. With proper grazing management and normal precipitation, these invader species normally do not persist for more than a few years.
Litter covers about 60% of the soil surface. Bare ground varies from 0 to Trace.
Rills should not be present and water flow patterns should be barely observable.
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 precipitation cycle.
Table 6. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
935 |
1360 |
1700 |
| Forb |
110 |
160 |
200 |
| Shrub/Vine |
55 |
80 |
100 |
| Total |
1100 |
1600 |
2000 |
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 |
50-60%
|
| Surface fragments >0.25" and <=3" |
0-3%
|
| Surface fragments >3" |
0-2%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0-1%
|
Table 8. Soil surface cover
| Tree basal cover |
0%
|
| Shrub/vine/liana basal cover |
1-3%
|
| Grass/grasslike basal cover |
20-30%
|
| 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 (ft) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.5 |
– |
0-20% |
0-10% |
0-40% |
| >0.5 <= 1 |
– |
0-40% |
0-30% |
0-50% |
| >1 <= 2 |
– |
0-30% |
0-40% |
0-8% |
| >2 <= 4.5 |
– |
0-10% |
0-20% |
0-2% |
| >4.5 <= 13 |
– |
– |
– |
– |
| >13 <= 40 |
– |
– |
– |
– |
| >40 <= 80 |
– |
– |
– |
– |
| >80 <= 120 |
– |
– |
– |
– |
| >120 |
– |
– |
– |
– |
Community 1.2
Plant Community A
Medium and tall cool-season perennial grasses, more than 10 percent perennial forbs, more than 5 percent shrubs
Shift in species composition, lower production, medium and tall cool-season perennial grasses, more than 10 percent perennial forbs, more than 5 percent shrubs
Total production averages about 1300 lbs/ac for this community, about 80% of the production in the HCPC. Vigor and production of the warm season bunchgrasses (little bluestem and sideoats grama) and tall cool season bunchgrasses (bluebunch wheatgrass, green needlegrass, porcupine grass) are reduced. Production of the rhizomatous midgrasses (western and thickspike wheatgrass) and the short cool (prairie junegrass, sandberg bluegrass) and warm (blue grama) increase. Production of needle and thread also increases as it tends to replace green needlegrass, especially on soils with with less moisture holding capacity.
Exact response by the lower successional species (blue grama, threadleaf sedge, sandberg bluegrass, fringed sagewort, silver sagebrush, etc.) vary with the kind of disturbance (drought, cattle, etc.) and with precipitation (amount and timing).
SI indices from 55-75% are associated with Plant Community A. In contrast to the HCPC, range conservationists have slight concerns regarding lower infiltration rates and potentially higher runoff rates, plant functional/structural group shifts, decreasing amount of litter, and increased presence of invasive plants.
Community 1.3
Plant Community B - Pre-Threshold Community
Medium and short-height cool and warm-season perennial grasses, increase of low-successional forbs, about 15 percent shrubs, bare ground equals 10 to 15 percent.
Medium and short-height cool and warm-season perennial grasses, increase of low-successional forbs, about 15 percent shrubs, total annual production at 800 lbs/ac, bare ground equals 10 to 15 percent.
Plant Community B is dominated by medium and short height cool and warm season perennial grasses. Production of western wheatgrass, thickspike wheatgrass and needle and thread (medium height grasses) is similar (from 300-400 lbs/ac) to total production of the short grasses and sedges (blue grama, prairie junegrass, sandberg bluegrass, threadleaf sedge, and plains reedgrass). Remnants of little bluestem, bluebunch wheatgrass and green needlegrass remain in communities within the central portions of the Glaciated Plains. These desirable bunchgrasses usually produce from 100-200 lbs/ac in this Plant Community.
Production of hairy goldenaster, scarlet globemallow, scurfpeas, hoods phlox, western yarrow and other lower-successional forbs increases relative to the production of the prairie clovers and American vetch. Production of lower successional forbs, fringed sagewort (half-shrub) and the native shrubs averages 320 lbs/ac. During the 2002-2004 range inventories conducted on the Fort Peck and Belknap Reservations, Similarity indices (SI) for this community varied from 25-55%.
Total forage production averages about 800 lbs/acre, a 50% decline from the high seral state. In contrast to the HCPC, range conservationists express moderate to high concerns about plant community composition, functional/structural groups, litter, annual production, and invasive plants. Although plant Community B is fairly resilient, 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 to Plant Community A would be restricted.
Pathway 1.1A
Community 1.1 to 1.2
No fire, no prescribed grazing, drought (3 to 5 years)
Transition pathways from the HCPC are influenced by non-prescribed grazing, drought, cessation of the natural fire regime, colonization and recruitment of noxious weeds, etc.
Pathway 1.2A
Community 1.2 to 1.1
Fire, prescribed grazing, normal precipitation
Plant Community A is resilient. Successional processes can readily return this community to the HCPC. Succession is facilitated by prescribed grazing and the incorporation of the natural fire regime. This process can occur during periods of normal precipitation.
Pathway 1.2B
Community 1.2 to 1.3
No fire, no prescribed grazing, prolonged drought (5 to 7 years)
Non-prescribed grazing, drought, colonization and recruitment of noxious weeds, and the continued absence of the natural fire regime will result in regression to Plant Community B.
Pathway 1.3A
Community 1.3 to 1.2
Fire, prescribed grazing, favorable precipitation
Successional processes can readily return Plant Community B to Plant Community A. Succession is facilitated by prescribed grazing, re-introduction of the natural fire regime, and a period of favorable precipitation.
State 2
Argillic Degraded State
Community 2.1
Plant Community C
Clubmoss, few warm- and cool-season short-height perennial grasses, lower-successional forbs, some invasive plants
Clubmoss, few warm- and cool-season short-height perennial grasses, lower-successional forbs, some invasive plants
Clubmoss, blue grama, sandberg bluegrass, and prairie junegrass dominate Plant Community C. At some locations, clubmoss will form a mat-like carpet over 30-70% of the ground. Although some western wheatgrass plants persist as single shoots with few seed stalks, it is difficult to find green needlegrass, little bluestem, bluebunch wheatgrass and other tall bunchgrasses. There are few seedlings of high-successional species emerging through the clubmoss-blue grama sod. Some researchers believe that this is due to an inadequate seedbank (Romo and Bai 2004).
Wooly plantain, hoods phlox, hairy goldenaster and scarlet globemallow are common forbs. Fringed sagewort and pricklypear cactus are usually common in this Community. Japanese brome, cheatgrass and a few annual forbs are distributed throughout the Community, but generally contribute less than 10% of the total production.
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. For example, when tall, high producing, cool season grasses are replaced by increasers (such as 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 clubmoss increases, it is theorized that 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 gain a competitive advantage over the deep rooted, cool season species. The biotic integrity of the site is degraded. Thus, the transition from Plant Community B (State #1) to Plant Community C (State #2) 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.
State 3
Non-Argillic Degraded State
Community 3.1
Plant Community D
Short, warm- and cool-season perennial grasses, few medium-height cool-season perennial grasses, lower-successional forbs, more than 20 percent shrubs, invasive species more prevalent.
Short, warm- and cool-season perennial grasses, few medium-height cool-season perennial grasses, lower-successional forbs, more than 20 percent shrubs, invasive species more prevalent.
Plant Community D is dominated by short height cool and warm season perennial grasses (blue grama, prairie junegrass, plains reedgrass, sandberg bluegrass). A few high-successional medium and tall height perennial grasses persist in this community. Production of Japanese brome and cheatgrass accounts for 10 of total annual production. Total annual production of this community normally varies from 400-600 lbs/ac.
Hairy goldenaster, scarlet globemallow, western yarrow, aster, biscuitroot, scurfpea, wallflower and other lower-successional forbs are common. In comparison to Plant Community B, production of fringed sagewort, prickly pear cactus and broom snakeweed generally increases significantly.
The ecological concerns described for Plant Community C are also inherent in Plant Community D. 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. For example, when tall, high producing, cool season grasses are replaced by increasers (such as 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. Without the thick clubmoss cover, the potential for erosion is actually higher in this community than it is in Plant Community C.
Community 4.1
Plant Community E
Former cropland that has been mostly seeded to perennial introduced grasses
Former cropland that has been mostly seeded to perennial introduced grasses
More than a million acres of former cropland in the Glaciated Plains have been 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. These programs spanned from the 1940s (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 wheatgrass, 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 majority of which occur on the Silty 10-14” p.z. ecological site.
The transition of these seeded communities from State #1 is depicted in the state-and-transition model. However, their future is not predicted. Depending on subsequent government programs and agricultural prices, these lands could stay in permanent vegetation with limited haying and grazing, be used as permanent pasture, or be converted to cropland.
Transition T1A
State 1 to 2
When soils have an argillic Horizon and go through extended drought (greater than 7 years), no prescribed grazing no fire
Plant Community B regresses to Plant Community C (State 2) determined by the presence of an argillic horizon.
Transition T1B
State 1 to 3
non-argillic, extended drought (greater than 7 years), no prescribed grazing, no fire
Plant Community B regresses to Community D (State 3)determined by the absence of an argillic horizon.
Transition T1C
State 1 to 4
Cultivation, seeding
Restoration pathway R2A
State 2 to 1
Mechanical treatment, seeding, prescribed grazing, normal precipitation
Plant Community C is a steady state. It is resistant to further disturbance, and it lacks the resiliency to return to the Reference State. Anecdotal reports indicate that succession from a clubmoss-dominated community can be facilitated with livestock impact (hoof action, urination, etc.). However, significant succession has not been documented in research studies. Therefore, it is recommended that mechanical treatment is required to return this plant community to the Reference State (State 1). Because the seedbank of high-successional species is believed to be inadequate, it may be necessary to seed desirable species following the mechanical treatment.
Restoration pathway R3A
State 3 to 1
Prescribed grazing, favorable precipitation, fire
Community D is fairly resistant. Further regression is unlikely with prescribed grazing and normal precipitation. As a steady state, this community is not highly resilient. Ecological concepts and perspectives suggest that succession from this Community to the Reference State 1 is not likely to occur without significant inputs (i.e., mechanical treatment). However, anecdotal information suggests that succession from Plant Community D to State 1 may occur when prescribed grazing is combined with an extended period of favorable precipitation. The rate of succession would be influenced by the presence of a high-quality seedbank.
