Ecological dynamics
Vegetation Dynamics:
Loamy Bottom ecological site produces about 3000 pounds per acre of biomass annually.
Regarding saline-alkali soils Daubenmire (page 50) wrote, “It seems impossible to find areas where one can be confident that the vegetation has not been somewhat altered by domesticated animals.” The same is also true of loamy bottoms, riparian areas and wetlands. Some areas were also manipulated by tillage or other farming practices.
Basin wildrye, also called Great Basin wildrye, is at the core of the Loamy Bottom ecological site and warrants a degree of understanding. Basin wildrye is a cool season bunchgrass but is considered weakly rhizomatous. It has coarse, robust stems and leaves, grows to 5 to 7 feet tall and sometimes exceeds three feet in diameter, and thus, is one of the highest producing species. Basin wildrye is commonly found on loamy bottoms, mildly to moderately saline-sodic soils and on the tops of loamy mounds. It tolerates alkaline soils and seasonal flooding but not anaerobic conditions. On a good Loamy Bottom ecological site, basin wildrye, given good plant vigor, can take ownership even with invasive species in the community.
Basin big sagebrush and Wyoming big sagebrush overlap in range and elevation. Basin big sagebrush plants are taller (up to 13 feet) and typically have a single main trunk. Wyoming big sagebrush is considerably shorter (3 to 5 feet), and plants have multiple main stems branching from the ground. Big sagebrush in a long-lived, multi-branched, evergreen shrub. Sagebrush has a significant rooting system, composed of a two-part rooting structure with a primary deep taproot, and a shallow extensive network of finer roots that spread laterally. This rooting system allows big sagebrush to survive in the hottest and driest portions of the sagebrush range by tapping into groundwater sources deep into the soil profile itself. This also allows sagebrush to be more competitive with bunchgrasses when the landscape positions and soils are less ideal for grass species to maintain the competitive advantage.
The stability and resiliency of the reference communities on Loamy Bottom ecological sites is directly linked to the health and vigor of basin wildrye. Given the opportunity (good vigor and favorable moisture), basin wildrye can establish ownership and expand across the Loamy Bottom ecological site. Basin wildrye expands via two processes: (1) Tillering from basal buds for new shoots, and (2) new seedlings from germinating seed.
The natural fire regime maintains a patchy distribution of shrubs. Depending on the time interval since the last fire, the shrub canopy can be as little 0 to 3 percent or as much as 40 percent.
The natural disturbance regime for sagebrush-bunchgrass communities is periodic lightning-caused fires. The fire return intervals (FRI) listed in research for sagebrush steppe communities is quite variable. Ponderosa pine communities have the shortest FRI of about 10 to 20 years (Miller). The FRI increases as one moves to wetter forested sites or to drier shrub steppe communities. Given the uncertainties and opinions of reviewers, a mean of 75 years and a range of 50 to 100 was chosen for Wyoming big sagebrush communities (Rapid Assessment Model). The FRI for Loamy Bottom ecological site is the same as upland sites.
Some fires are spotty or do not burn hot enough to fully remove the sagebrush. Fires with light severity will remove less sagebrush and open smaller patches for grass and forb recovery, whereas the more severe fires will remove almost all the sagebrush and leave vast areas open to return to bunchgrass dominance. This is how the patchy distribution occurs. Rabbitbrush is a sprouting shrub and may also increase following fire.
Because basin wildrye produces a large amount of biomass, fire can burn and smolder in the crown of the plant for considerable time. This leaves basin wildrye plants much diminished. It can take a few years for basin wildrye to fully recover from the effects of fire.
Grazing is another common disturbance that occurs to this ecological site. Grazing pressure can be defined as heavy grazing intensity, or frequent grazing during reproductive growth, or season-long grazing. As grazing pressure increases the plant community unravels in stages:
1. More preferred grasses decline first and then basin wildrye plants produce fewer shoots and tillers and crowns become smaller.
2. As some basin wildrye plants die and other plants are weaker yet, native species such as sagebrush expands
3. As the decline continues invasive species such as knapweed, perennial pepperweed and cheatgrass colonize the site
4. With further decline the site can become a sagebrush-invasive weed community
Managing sagebrush steppe to improve the vigor and health of native bunchgrasses begins with an understanding of grass physiology. New growth for existing bunchgrasses begins each year from basal buds. Basin wildrye plants can expand via tillering, or new plants through natural reseeding. Regrowth from spring grazing comes mostly from photosynthesis.
In the spring each year it is important to monitor and maintain an adequate top growth: (1) to optimize regrowth following spring grazing, (2) so plants have enough energy to replace basal buds annually, and (3) to protect the elevated growing points of basin wildrye.
During seed formation, the growing points of basin wildrye become elevated 4 to 6 inches and are vulnerable to damage or removal. Repeated grazing during late spring is especially damaging. Over several years each native bunchgrass pasture should be rested during the critical period two out of every three years (approximately April 15through July 15). And each pasture should be rested the entire growing-season every third year (approximately
March 1 through July 15).
Basin wildrye and bluebunch wheatgrass remain competitive if:
(1) Basal buds are replaced annually,
(2) Enough top-growth is maintained for growth and protection of growing points, and
(3) The timing of grazing and non-grazing is managed over a several-year period. Careful management of late spring grazing is especially critical
In Washington, basin wildrye-sagebrush communities provide habitat for a variety of upland wildlife species.
State 1
Reference
State 1 represents sagebrush steppe with none to minor amounts of invasive or exotic weed species. All the functional, structural groups have one or more native species. Reference Community 1.1 is dominated by basin wildrye with some sagebrush. Community 1.2 is even more strongly bunchgrass dominated. Community 1.3 is dominated by sagebrush with basin wildrye as sub-dominate. Native forbs and other shrubs are prevalent and there are minor amounts of weeds (broadleaf or annual grasses). There is enough basin wildrye remaining for Community 1.3 to shift back to the other communities in the reference state as basin wildrye can be aggressive on favorable sites such as Loamy Bottom ecological site. On a good Loamy Bottom ecological site basin wildrye can and will push out other herbaceous species. At-risk Communities: • All communities in the reference state are at risk of invasion by exotic species. Annual or biennial weeds and annual grass seeds blow onto most sites annually • Community Phase 1.3, the heavy sagebrush community, has the highest risk of moving to State 2 which is dominated by invasive weeds or annual grasses • Any Loamy Bottom ecological site plant community with high sagebrush cover and low cover of basin wildrye will also have some invasive weeds • To seed or not to seed is the question after a fire. Community 1.3 should be seeded to basin wildrye to minimize weed infestation. Any site with low cover of basin wildrye and any site with low to moderate cover of weeds should be seeded after a fire. State 2 and Community 3.2 should also be seeded
Community 1.1
Basin Wildrye, Basin Big Sagebrush, and Wyoming Big Sagebrush
50% basin wildrye
25% bluebunch wheatgrass
10% Wyoming big sagebrush and basin big sagebrush
5% native forbs
Community 1.2
Basin wildrye and Bunchgrass
60% basin wildrye
25% bluebunch wheatgrass
5% sagebrush
10% native forbs
Community 1.3
Sagebrush
15% basin wildrye and bluebunch wheatgrass
50% sagebrush
25% other shrubs, native forbs, and other grasses
10% weeds
Pathway 1.1A
Community 1.1 to 1.2
Result: Shift from reference community 1.1 to bunchgrass community 1.2. Sagebrush cover is all but eliminated, while basin wildrye has a moderate increase in cover. Primary Trigger: Moderate-severity fire consumes above-ground plant biomass and kills almost all the sagebrush. With a lot of biomass, the fire burns into the crowns of basin wildrye, but some of the crown remains intact. So, basin wildrye survives and increases its vigor the next few years. For other bunchgrasses and forbs there is no impact to their crowns and these species return post-fire with good vigor. Post-fire the bunchgrasses are now more susceptible to grazing damage. Burned rangeland pastures need two growing seasons rest before grazing resumes or, the pastures can be lightly grazed during the dormant season the first two years post-fire. Beyond two years for the bunchgrasses to expand, moderate grazing intensity, and both critical period and growing season deferments must be implemented on burned pastures. Secondary Trigger: Several years above of average precipitation. High seasonal water table kills most of the sagebrush, allowing basin wildrye to assert almost total cover dominance. This is a rare occurrence, but it did happen in the mid-1980s. Ecological process: Fire kills sagebrush and it does not have any sprouting ability. A few sagebrush plants remain, but only in patches that did not burn. The reduction in sagebrush releases resources and increases light for grasses and forbs. Basin wildrye, bluebunch wheatgrass and other bunchgrasses have good vigor post-fire and expand via tillering and new seedlings.
Pathway 1.1B
Community 1.1 to 1.3
Result: shift from reference community 1.1 to heavy sagebrush community 1.3. Primary Trigger: With excessive grazing pressure (heavy grazing intensity, season long grazing or frequent late spring grazing) and a period of no fire, sagebrush increases its cover while basin wildrye, bluebunch wheatgrass and other bunchgrasses suffer a big decline. Ecological process: with consistent defoliation pressure basin wildrye and other bunchgrass have low vigor, shrinking crowns and some mortality. This gives sagebrush the opportunity to set new seedlings and expand its cover. Increased shade from the new sagebrush plants also plays a role in this process.
Pathway 1.2A
Community 1.2 to 1.1
Result: Shift from bunchgrass community 1.2 to reference community 1.1. Primary Trigger: Soil disturbances coupled with a period of no fire. Secondary Trigger: Several years of average or below normal precipitation leading to a significant drop in the lateral water flow and drying out the soil profile, which leads to fine root die-off of basin wildrye. Slight competitive advantage shifts to sagebrush. Good management is required to keep the basin wildrye loss to a minimum as sagebrush re-enters the community Ecological process: Spots with soil disturbance receive sagebrush seed from remnant plants in unburned patches or from adjacent sites, seed germinates in the spring and a few sagebrush seedlings establish. For most locations it may take up to 10 years for sagebrush to re-enter the community. With a slight increase in shade perennial bunchgrasses experience a slight decline.
Pathway 1.3A
Community 1.3 to 1.1
Result: Significant shift from heavy sagebrush community 1.3 to reference community 1.1. Primary Trigger: Moderate-severity fire consumes above-ground plant biomass and kills almost all the sagebrush. With a lot of biomass, the fire burns into the crowns of basin wildrye, but some of the crown remains intact. So, basin wildrye survives and increases its vigor the next few years. For bunchgrasses and forbs there is no impact to their crowns and these species return post-fire with good vigor. Post-fire the bunchgrasses are now more susceptible to grazing damage. Burned rangeland pastures need two growing seasons rest before grazing resumes or, the pastures can be lightly grazed during the dormant season the first two years post-fire. Beyond two years for the bunchgrasses to expand, moderate grazing intensity, and both critical period & growing season deferments must be implemented on burned pastures. Secondary Trigger: Several years above of average precipitation. High seasonal water table kills most of the sagebrush, allowing basin wildrye to assert almost total cover dominance. This is a rare occurrence, but it did happen in the mid-1980s. Ecological process: Fire kills sagebrush and it does not have any sprouting ability. A few sagebrush plants remain, but only in patches that did not burn. The reduction in sagebrush releases resources and increases light for grasses and forbs. Basin wildrye can aggressively attains the competitive edge and reclaims niches vacated by sagebrush. Bluebunch wheatgrass and other bunchgrasses have good vigor post-fire and expand via tillering and new seedlings.
State 2
Invaded
State 2 represents communities that have crossed a biological threshold. Invasive species dominate the site and virtually all the native functional, structural groups are missing. This state can occur with or without sagebrush. Dominant State 2 Species: Invasive weeds: mustard, prickly lettuce, perennial pepperweed, knapweeds Invasive annual grasses: annual bromes, cheatgrass Sagebrush, rabbitbrush R2 No Recovery within reason. Result: Shift from invasive species in State 2 back to Reference State. This restoration transition does not occur without a significant commitment of time & resource inputs to restore ecological processes, native bunchgrasses, sagebrush and native forb species. TWO OPTIONS: Option#1: Step 1 seed to introduced grasses; Step 2 seed to native species Step 1 shifting from State 2 to State 3: It will take two years or longer to kill annual species and to exhaust the seedbank of invasive weed seed. Site will then need to be seeded to introduced perennial species such as crested wheatgrass to restore soil properties before native species can survive and thrive on site. The seeded species rebuild some of the basic soil properties including increased soil organic matter, improved pore spaces and increased soil moisture within the soil profile. The site would also need several years of no significant fires and proper grazing management as well. See narrative for R1 recovery above. Step 2 shifting from State 3 to State 1: This assumes that the shift from State 2 to State 3 has been successful. Introduced grasses and any remaining weeds must be killed while maintaining soil structure to ensure a proper seedbed (cloddy, a little rough and trashy to provide safe sites for the seed). A pulverized dust mulch must be avoided at all costs. The seeding of native species could occur in two steps: (1) first year, use a grass seed mix to duplicate the Reference Community (mostly basin wildrye with other native bunchgrasses) so that broadleaf weeds may be controlled, and (2) second year re-introduce sagebrush and native forbs. Plugs may be used for sagebrush and native forbs rather than seed. Post-seeding the site would also need several years with no significant fires and proper grazing management as well to ensure plant establishment and vigor. Option #2: seed directly to native species Take two years or more to kill weeds and to exhaust the weed seedbank while maintaining soil structure. As in Option 1 above, the seeding of native species could occur in two steps: (1) first year, use a grass seed mix to duplicate the Reference Community (mostly basin wildrye with other native bunchgrasses) so that broadleaf weeds may be controlled, and (2) second year re-introduce sagebrush and native forbs. Plugs may be used for sagebrush and native forbs rather than seed. Post-seeding the site would also need several years with no significant fires and proper grazing management as well to ensure plant establishment and vigor.
Community 2.1
Invasive Annual and Biennial Weeds and Invasive Annual Grasses
State 3
Seeded
State 3 represents a site that has been seeded to desirable grasses such as basin wildrye or intermediate wheatgrass. Community 3.1 remains stable with 0.8 plant per square foot or greater of mid-sized bunchgrasses or with a full stand of basin wildrye.
Community 3.1
Seeded Grasses
Community 3.2
Shrubs and Seeded Grasses
Pathway 3.1A
Community 3.1 to 3.2
Result: shift from seeded grass community 3.1 to shrub grass community 3.2 with a mixture of seeded grasses and shrubs and invasive weeds Primary Trigger: Grazing pressure (heavy grazing intensity, season long grazing or frequent late spring grazing) to seeded grasses Ecological process: Due to consistent defoliation pressure seeded grass have low vigor, shrinking crowns and some mortality. This gives sagebrush the opportunity to set new seedlings and expand its cover. Increased shade from the new sagebrush plants also plays a role in this process.
Pathway 3.2A
Community 3.2 to 3.1
Result: shift from shrub/weed dominated community 3.2 back to community 3.1 dominated by seeded grasses. Primary Trigger: Human intervention to kill shrubs, reduce invasive weed population and to re-seed or inter-seed desirable grass species. Ecological process: shrub and weed control open the site to allow successful seeding. Herbicide application, tillage and seeding operation must be timely. Seed placement should ensure seed-soil contact at 1/8 to 1/4 inch depth. Post-seeding management should ensure that desirable grass seedlings become established and broadleaf weeds are controlled. After killing shrubs and weeds, and with a good population of remnant desirable grasses, it may be possible that the desirable grasses expand naturally without seeding.
Transition T1A
State 1 to 2
Result: Shift from Reference State (native shrub steppe with no invasive species) to State 2 which is dominated by invasive weeds or annual grasses. The pathway from State 1 to State 2 occurs as Community 1.3 declines until it crosses the biological threshold. This transition occurs once the cover of basin wildrye drops to 5 percent and invasive species cover is at least 40 percent. Primary Trigger: grazing pressure (heavy grazing, season-long grazing, or late spring grazing) to basin wildrye. Secondary Trigger: Frequent fires or one severe fire can have the same effect. Also, several years of drought can put the basin wildrye in decline. Ecological process: with consistent defoliation pressure basin wildrye and other bunchgrass have low vigor, shrinking crowns and mortality. Weed seeds from invasive species blow onto the site or are carried in with runoff water. On most sites weed seeds are waiting for an opportunity to colonize. As basin wildrye cover declines invasive species increase accordingly. Over time the invasive species expand to a position of dominance. Indicators: Decreasing cover of basin wildrye and increasing cover of invasive species. Increasing canopy gaps between native perennial species. Decreasing soil organic matter, soil water retention, limited water infiltration and percolation in the soil profile.
Restoration pathway R2A
State 2 to 3
This restoration transition does not occur without significant time and inputs to control weeds, prepare a seedbed, seed desirable species, and post-seeding weed control and management. This can require a commitment of two years or more for weed control. Care must be taken to maintain soil structure so that the seedbed has many safe-sites for the seed. Seed placement must be managed to achieve seed-soil contact at very shallow depth (about 1/8-1/4 inch is desired). Proper grazing management is essential to maintain the stand post-seeding. Basin wildrye and intermediate wheatgrass are highly adapted to the Loamy Bottom ecological site. The actual transition occurs when the seeded species have successfully established and are outcompeting the annual species for cover and dominance of resources.
Transition T3A
State 3 to 2
Result: Shift from State 3 (seeded grasses) to State 2 which dominated by invasive weeds or annual grasses. Primary Trigger: grazing pressure (heavy grazing, season long grazing, or frequent late spring grazing) to seeded grasses. Secondary Trigger: Frequent fires or a severe fire that burn out plant crowns of native species and give competitive advantage to the invasive species. This transition occurs when chronic heavy grazing has removed too much of the perennial bunchgrass cover allowing invasive annual species to colonize the site. As this continues the competitive advantage goes to the exotic species which are opportunistic and take most of the site’s resources. Ecological process: with consistent defoliation pressure seeded grasses have low vigor, shrinking crowns and mortality. Weed seeds from invasive species blow onto the site or are carried in with runoff water. On most sites weed seeds are waiting for an opportunity to colonize. As the cover of seeded grass declines invasive species increase accordingly. Over time the invasive species expand to a position of dominance. Indicators: shrinking crowns and mortality of desirable species, increasing gaps between perennial species, and increasing cover by invasive annual species.
