Ecological site group description

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

Physiography

Hierarchical Classification
Major Land Resource Area (MLRA): 9 – Palouse and Nez Perce Prairie

LRU – Common Resource Areas (CRA):
9.1 - Channeled Scablands
9.12 - Moist Loess Islands
9.2 - Palouse Hills
9.3 - Dissected Loess Uplands
9.4 - Deep Loess Foothills
9.5 - Warm Canyons and Dissected Uplands

Site Concept Narrative:

In the upland setting ecological sites are often expansive, and thus, can be delineated and separated on aerial photos. But in the landscape position of bottoms, basins and depressions this is rarely the case as small changes in soil chemistry, the water table and elevation or aspect results in significant changes in plant community composition. In short distances there are often big swings of available water holding capacity, and soils can go from hydric to non-hydric, or from saline-sodic to not. So, in bottoms, riparian areas and depressions, ecological sites and community phases occur as small spots, strips and patches, or as narrow rings around vernal ponds. And generally, in a matter of steps one can walk across several ecological sites. On any given site location, two or more of these sites occur as a patchwork – Loamy Bottom, Alkali Terrace, Sodic Flat, Wet Meadow, Herbaceous Wetland and Riparian Woodland. These ecological sites may need to be mapped as a complex when doing resource inventory.

Diagnostics:

The first thing you notice about Loamy Bottom is the much taller vegetation and vastly more production than any upland site. The tall, upright bunchgrasses can be taller than 6 feet. Another striking feature of Loamy Bottom is that it provides excellent protection from wind for livestock and wildlife, and good habitat (hiding cover, nesting cover, standing winter forage).

Loamy Bottom is part of the lentic (standing water) ecosystem, but this site is not a wetland, nor or the soils hydric. It occurs on moisture receiving sites such as bottoms, draws, basins and depressions. This site also occurs as a narrow zonal ring around ponds, lakes and vernal pools. Loamy bottom is an important “hinge site” as it connects upland sites with riparian areas, wetlands and saline-sodic sites.

Soils are deep and unrestricted for plant growth. The soils are silt loam or sandy loam texture and are not saline or sodic, and not hydric. In addition, the landscape position of this site could be conducive to soils possibly containing andic soil properties, i.e. volcanic ash. These andic soil properties can be important for productivity in that they retain larger amounts of water compared to other parent materials (higher water-holding capacity (AWC)), have high cation exchange capacity (CEC) and high availability of organically bound plant nutrients.

Across the sagebrush steppe region in MLRA 8, this site is a basin wildrye-sagebrush site. Within MLRA 9, Loamy Bottom has several variations with basin wildrye as the constant in all instances. In the channel scablands area threetip sagebrush and basin big sagebrush are prevalent. But in the loess hills, the only shrub, rabbitbrush, is a minor component, and the site is exclusively dominated by basin wildrye in the reference condition. In the Palouse Hills basin wildrye with rose and snowberry are present. The variations are lumped into one ecological site because Loamy Bottom represents only a fraction of the landscape and basin wildrye is dominant in every variation. Also, use, management and production are similar across all variations.

While tall bunchgrasses dominate the reference state overstory, mid-sized bunchgrasses and forbs fill the interspaces. The overstory layer is head-high or taller basin wildrye. Cool-season bunchgrasses form one or two distinct understory layers. Bluebunch wheatgrass or Nelson’s needlegrass, if present, form the mid-grass layer, while Sandberg bluegrass is the shortest grass layer.

Virtually all the Loamy Bottom sites have been farmed in the Palouse. Loamy Bottom in the channeled scabland and loess hills have been heavily disturbed as well.

Principle Vegetative Drivers:

The vegetative expression of Loamy Bottom is driven by three situations. First, this site receives both surface runoff and discharging groundwater from adjacent upland ecological sites. Second, the soils are deep and have unrestricted rooting. Third, the soils are well drained and remain in an anaerobic condition for only a short period of time. This makes Loamy Bottom far more productive than any upland site.

Influencing Water Features:

A plant’s ability to grow on a site and overall plant production is determined by soil-water-plant relationships:
1. Whether rain and melting snow run off-site or infiltrate into the soil
2. Whether soil condition remain aerobic or become saturated and anaerobic
3. How quickly the soil reaches the wilting point

Loamy Bottom receives both surface runoff and discharging groundwater from nearby upland sites. The soils are deep, well drained, and unrestricted, and thus, remain saturated for only a short period in late winter to early spring. With adequate cover of live plants and litter, there are no water infiltrating restrictions on Loamy Bottom.

Physiographic Features:

The landscape is part of the Columbia basalt plateaus and Northern Rocky foothills.

In the upland setting ecological sites are often expansive, and thus, can be delineated and separated on aerial photos. But in the landscape position of bottoms, basins and depressions this is rarely the case as small changes in soil chemistry, the water table and elevation or aspect results in significant changes in plant community composition. In short distances there are often big swings of available water holding capacity, and soils can go from hydric to non-hydric, or from saline-sodic to not. So, in bottoms, riparian areas and depressions, ecological sites and community phases occur as small spots, strips and patches, or as narrow rings around vernal ponds. And generally, in a matter of steps one can walk across several ecological sites. On any given site location, two or more of these sites occur as a patchwork – Loamy Bottom, Alkali Terrace, Sodic Flat, Wet Meadow, Herbaceous Wetland and Riparian Woodland. These ecological sites may need to be mapped as a complex when doing resource inventory.

Loamy bottom covers all three geographic areas covered in PESs of MLRA 9; Channeled Scablands, Palouse Hills, and Loess Hills.

Physiographic Division: Intermontane Plateau and Northern Rocky Mountain System
Physiographic Province: Columbia Plateau and Northern Rocky Mountains
Physiographic Sections: Walla Walla Plateau and Blue Mountain Section

Landscapes: hills and plateaus
Landform: floodplains, drainageways, terraces

Elevation: Dominantly 1,000 to 4,000 feet
Slope: Total range: 0 to 5 percent
Central tendency: 0 to 3 percent
Aspect: Occurs on all aspects

Geology:

MLRA 9 is almost entirely underlain by Miocene basalt flows. Columbia River basalt is covered by wind-blown loess with a thickness up to 246 feet thick. The oldest layer of loess accumulated between 2 and 1 million years ago, while the uppermost layers of Palouse Loess accumulated between 15,000 years ago and modern times. The mid layers of loess were deposited episodically between 77,00 year and 16,00 years ago. The Palouse Loess largely consists of the wind-blown sediments eroded from the Hanford formation that were periodically deposited by repeated Missoula Floods within the Eureka Flats area.

Climate

The climate across MLRA 9 is characterized by moderately cold, wet winters, and relatively dry summers. The climate is characterized by moderately cold, wet winters, and hot, dry summers, with limited precipitation due to the rain shadow effect of the Cascades. Taxonomic soil climate is primarily a xeric moisture regime and mesic temperature regime.

Mean Annual Precipitation:
Range: 16 – 28 inches
Winter precipitation, primarily snow, occurs during low-intensity, Pacific-frontal storms. During winter these storms produce occasional rains that fall on frozen or thawing ground surfaces. High intensity, convective thunderstorms produce some rain during the growing season. Precipitation is evenly distributed throughout fall, winter and spring.

Mean Annual Air Temperature:
Range: 42 to 52 F
Central Tendency: 47 – 50 F
Freezing temperatures generally occur from late-October through early-April. Temperature extremes are -10 degrees in winter and 110 degrees in summer. Winter fog is variable and often quite localized, as the fog settles on some areas but not others.

Frost-free Period (days):
Total range: 60 to 180
Central tendency: 100 to 140
The growing season for Loamy Bottom is March through August.

Soil features

Edaphic:

The soils are deep, well drained and formed in loess. Loamy Bottom commonly occurs adjacent to Wetland complex, Riparian complex and one of the Loamy ecological sites.

Representative Soil Features:

This ecological site components are dominantly Cumulic and Vitrandic taxonomic subgroups of Haploxerolls great groups of the Mollisols taxonomic order. Soils are dominantly very deep. Average available water capacity of about 8 inches (20.3 cm) in the 0 to 40 inches (0-100 cm) depth range.

Soil parent material is dominantly mixed alluvium derived from loess possibly mixed with minor amounts of ash in the upper part of the soil.

The associated soils are Caldwell, Mondavi and similar soils.

Dominate soil surface is silt loam to cobbly loam, with ashy modifier sometimes occurring as well.

Dominant particle-size class is fine-silty to course-loamy.

Fragments on surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 5

Fragments within surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 5
Average: 1

Fragments within surface horizon ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 5
Average: 1

Subsurface fragments > 3 inches (% Volume):
Minimum: 0
Maximum: 5
Average: 2

Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 15
Average: 2

Drainage Class: Range from somewhat poorly drained to moderately well drained.
Water table depth: 20 to greater than 50 inches

Flooding:
Frequency: None to Occasional

Ponding:
Frequency: None

Saturated Hydraulic Conductivity Class:
0 to 10 inches: Moderately high
10 to 40 inches: Moderately high

Depth to root-restricting feature (inches):
Minimum: Greater than 60
Maximum: Greater than 60

Electrical Conductivity (dS/m):
Minimum: 0
Maximum: 0

Sodium Absorption Ratio:
Minimum: 0
Maximum: 0

Calcium Carbonate Equivalent (percent):
Minimum: 0
Maximum: 0

Soil Reaction (pH) (1:1 Water):
0 - 10 inches: 5.6 to 8.4
10 - 40 inches: 5.6 to 9.0

Available Water Capacity (inches, 0 – 40 inches depth):
Minimum: 5.7
Maximum: 8.9
Average: 8

Vegetation dynamics

Ecological Dynamics:

Loamy Bottom produces about 3000-5000 pounds/acre of biomass annually.

Loamy Bottom has several variations with basin wildrye as the constant:
1. Basin wildrye – three-tip sagebrush, basin big sagebrush (Channeled Scabland)
2. Basin wildrye with no shrub in the loess hills area (a little rabbitbrush)
3. Basin wildrye – rose/snowberry (Palouse Hills)

Regarding saline-alkali soils Daubenmire 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. These areas have been heavily grazed, and drained, filled or straightened to enable farming.

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 3 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.

The stability and resiliency of the reference communities on Loamy Bottom 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 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 10-20 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 50-100 was chosen for Wyoming sagebrush communities (Rapid Assessment Model). The FRI for Loamy Bottom is the same as upland sites. This would place the historic FRI for grassland steppe around 30-50 years.

The shrubs on Loamy Bottom – threetip sagebrush, rabbitbrush, rose and snowberry – all sprout 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.
2. Basin wildrye plants produce fewer shoots as crowns become smaller. Unpalatable forbs increase.
3. As the decline continues invasive species such as knapweed, perennial pepperweed and annual grasses colonize the site
4. With further decline the site can become a shrub-invasive weed community

Managing grasslands 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 4-6 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 15–July 15). And each pasture should be rested the entire growing-season every third year (approximately March 1 – 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-sagebrush communities provide habitat for a variety of upland wildlife species.


Supporting Information:

Associated Sites:
Loamy Bottom is associated with other ecological sites in bottoms and basin areas of MLRA 9, including Wetland Complex, Riparian Complex, Loamy bunchgrass,
Loamy dwarf shrub, Shallow Stony, and Cool Loamy.

Similar Sites:
MLRAs 6, 7 & 8 have a similar Loamy Bottom ecological site.

Inventory Data References (narrative):
Data to populate Reference Community came from several sources: (1) NRCS ecological sites from 2004, (2) Soil Conservation Service range sites from 1980s and 1990s, (3) Daubenmire’s habitat types, and (4) ecological systems from Natural Heritage Program

Major Land Resource Area

MLRA 009X
Palouse and Nez Perce Prairies

Subclasses

• R009XY930WA–Loamy Bottom

Stage

Provisional

Contributors

Kevin Guinn, C. Smith, R. Fleenor, K. Paup-Lefferts