Ecological dynamics
Alkali Terrace produces about 3,000 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.” Some areas were also manipulated by tillage or other farming practices.
Basin wildrye, also called Great Basin wildrye, and inland saltgrass are at the core of the Alkali Terrace ecological site and warrant a degree of understanding. Basin wildrye is a tall, cool-season bunchgrass and has coarse, robust stems and leaves. It grows five to seven feet tall and sometimes exceeds three feet in diameter and, is one of the highest producing species. Basin wildrye is commonly found on loamy bottoms, saline-alkali soils and on the tops of loamy mounds. It tolerates alkaline soils and seasonal flooding but not anaerobic conditions. Basin wildrye is considered weakly rhizomatous.
Saltgrass is a short, warm-season, sod-forming grass that can form dense mats with its rhizomes and sometimes stolons. Saltgrass is one of the most common plants found on saline-alkaline soils. It is one of the most drought tolerant species. Being rhizomatous, saltgrass is tolerant of moderate to heavy grazing.
The natural disturbance regime for grassland 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 dries 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 sagebrush communities (Rapid Assessment Model).
Because basin wildrye produces a large amount of biomass, fire can burn and smolder in the crown of the plant for considerable time. This can leave basin wildrye plants much diminished. It can take years for basin wildrye to fully recover from the effects of fire. Saltgrass, being rhizomatous, is quite tolerant of fire, but due to limited fuel, often does not burn.
Grazing is another common disturbance that occurs in 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. Basin wildrye plants produce fewer shoots and tillers and become smaller allowing saltgrass to expand
2. As the decline continues invasive species such as perennial pepperweed and cheatgrass colonize the site
3. With further decline the site can become an invasive weed community
Saltgrass is quite tolerant of grazing, and as a warm-season grass it provides green forage a little longer than adjacent upland sites. Basin wildrye is not tolerant of heavy grazing especially in late spring when the growing points are elevated 4 to 6 inches above the soil surface. For Loamy Bottom, basin wildrye should be the key species to manage and monitor.
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.
During seed formation, the growing points of basin wildrye become elevated four to six 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 15 to July 15). And each pasture should be rested the entire growing season every third year (approximately March 1 to July 15).
Basin wildrye remains 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 and saltgrass communities provide habitat for a variety of upland wildlife species.
State 1
Reference Grassland Steppe with No Invasive Species
State 1 represents Alkali Terrace with no invasive or exotic species. All the functional, structural groups have one or more species. By cover saltgrass dominates the Reference Community By weight basin wildrye dominates the Reference Community Reference State Community Phases: 1.1 Reference Basin wildrye – Saltgrass 1.2 Rhizomatous Saltgrass – Basin wildrye Dominate Reference State Species: Basin wildrye, saltgrass At-risk Communities: • All communities in the reference state are at risk of invasive species. Annual or biennial weeds and annual grass seeds blow onto most sites annually
Community 1.1
Basin Wildrye and Saltgrass
65% basin wildrye
20% saltgrass
10% other native grasses
Community 1.2
Saltgrass and Basin Wildrye
25% basin wildrye
60% saltgrass
10% alkali cordgrass
Pathway 1.1A
Community 1.1 to 1.2
Result: Shift from Reference Community 1.1 (Basin Wildrye and Saltgrass) to Community 1.2 (Saltgrass and Basin Wildrye). Basin wildrye declines while saltgrass makes a corresponding increase. Also, alkali bluegrass declines and alkali cordgrass increases. Primary Trigger: Excessive grazing pressure (heavy grazing intensity, season long grazing or frequent late spring grazing) to basin wildrye. Ecological process: with consistent defoliation pressure basin wildrye and has low vigor, shrinking crowns and some mortality. Saltgrass rhizomes move into the areas vacated by basin wildrye and new saltgrass shoots become established.
Pathway 1.2A
Community 1.2 to 1.1
Result: Shift from rhizomatous grass community 1.2 back to Reference Community 1.1 with more bunchgrasses. Primary Trigger: Light to moderate grazing especially during dormant season, coupled with favorable moisture years allows basin wildrye to expand. Ecological process: Given the opportunity (good vigor and adequate soil moisture) basin wildrye plants gain the competitive edge and re-establishes dominance via tillering and new seedlings.
State 2
Invasive Species
State 2 represents Alkali Terrace where invasive broadleaf weeds and/or invasive annual grasses have prominence. Basin wildrye is all but missing and saltgrass remains as a patchwork of spots and clumps. State 2 can have two variations, both with or without rabbitbrush: 1. Broadleaf annual or biennial weeds with saltgrass patches 2. Annual grasses with saltgrass patches Community Phases for State 2: Invasive broadleaf annual or biennial weeds with patches of saltgrass Invasive annual grasses with patches of saltgrass Some Invasive Species in State 2: cheatgrass slender cinquefoil rabbitsfoot grass foxtail barley perennial pepperweed
Community 2.1
Invasive Species
Invasive annual and biennial broadleaf weeds with or without rabbitbrush
Foxtail barley
State 3
Seeded Grasses
State 3 represents a site that has been seeded to desirable grasses such as basin wildrye, beardless wildrye, tall wheatgrass, or western wheatgrass. Community Phases for State 3: 3.1 Seeded Grass 3.2 Shrub – Seeded Grass
Community 3.1
Seeded Grasses
85% seeded grasses
Community 3.2
Shrubs and Seeded Grasses
50% shrubs
40% seeded grasses
Pathway 3.1A
Community 3.1 to 3.2
Result: Shift from Community 3.1 Seeded Grasses to community 3.2 Shrub and Seeded Grasses. Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to desirable seeded grasses. Ecological Process: with consistent grazing pressure, seeded grasses have poor vigor, shrinking crowns and some mortality. Rabbitbrush seed which blows onto the site establishes a crop of seedlings. Rabbitbrush cover expands as the shrubs grow.
Pathway 3.2A
Community 3.2 to 3.1
Result: Shift from Community 3.2 shrub-seeded grasses to Community 3.1 seeded grasses Primary Trigger: chemical spraying to kill rabbitbrush coupled with proper grazing management. A good remnant population of basin wildrye in good vigor is required to respond to the herbicide treatment. Ecological Process: chemical spray kills rabbitbrush plants and this release resources. Basin wildrye expands via tillering and new seedlings.
Transition T1A
State 1 to 2
Result: Shift from Reference State to State 2 with invasive species Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to basin wildrye. Ecological process: with consistent grazing pressure basin wildrye has poor vigor, shrinking crowns and mortality. Initially, saltgrass increases but then declines with further grazing pressure. Invasive species colonize and as the deterioration continues, eventually dominate the site. Indicators: Increasing gaps between basin wildrye plants, decreasing cover of saltgrass and increasing cover of invasive species.
Restoration pathway R2A
State 2 to 3
Transition from State 2, a community dominated by invasive annual species, to State 3, which is predominately desirable seeded grasses. Species selection for the seeding is critical as the site is moderately saline-sodic. 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. It may take two years or longer to kill invasive annual species and remaining saltgrass, and to exhaust the seedbank of invasive weed seeds. 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 a very shallow depth (about 1/8 inch is desired). Species that can tolerate the saline-sodic conditions include basin wildrye, beardless wildrye, tall wheatgrass, and western wheatgrass. Proper grazing management is essential to maintain the stand post-seeding. 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 with invasive species Primary Trigger: Grazing pressure (heavy intensity, season long grazing, frequent late spring grazing) to desirable seeded grasses. Ecological Process: with consistent grazing pressure desirable grasses have poor vigor, shrinking crowns and mortality. This allows invasive species to colonize and then expand to a position of dominance. Indicators: increasing gaps between basin wildrye plants, increasing cover of invasive species
