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): 8 – Columbia Plateau

LRU – Common Resource Areas (CRA):
8.1 - Channeled Scablands
8.2 - Loess Islands
8.3 - Okanogan Drift Hills
8.4 - Moist Pleistocene Lake Basins
8.5 - Moist Yakima Folds
8.6 - Lower Snake and Clearwater Canyons
8.7 - Okanogan Valley


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 that strikes you about Loamy Bottom – the vegetation is much taller, and vastly more productive than any upland site. The tall, upright bunchgrasses and shrubs 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 provides 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.

Within MLRA 8, Loamy Bottom has several variations with basin wildrye as the constant in all instances. Across most of the sagebrush steppe region, this site is a basin wildrye-basin or Wyoming big sagebrush site. In Douglas County and southern Okanogan County threetip sage is prevalent. But in the grassland regions the only shrub, rabbitbrush, is a minor component. The last variation is basin wildrye-rose. 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 is similar across all variations.

While tall bunchgrasses and tall, fire-sensitive shrubs dominate the reference state overstory, mid-sized bunchgrasses and forbs fill the interspaces. The overstory layer is basin wildrye with head-high or taller Basin big or Wyoming big sagebrush. 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.

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 0-3% or as much as 40%.


Principle Vegetative Drivers:

The vegetative expression of Loamy Bottom is driven by two situations. First, this site receives both surface runoff and discharging groundwater from adjacent upland ecological sites. Second, the soils are deep and unrestricted. This makes Loamy Bottom far more productive and 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 plateau. Loamy bottom sites commonly occur on non-wetland bottoms, draws, basins, & depressions and often loamy bottom is one of the narrow bands around ponds, lakes, vernal pools, springs and seeps. 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. 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, Wetland Complex and Riparian Complex. These ecological sites may need to be mapped as a complex when doing resource inventory.

Physiographic Division: Intermontane Plateau
Physiographic Province: Columbia Plateau
Physiographic Sections: Walla Walla Plateau Section

Landscapes: Hills, valleys and plateaus
Landform: Floodplains, drainageways and depressions

Elevation: Dominantly 500 to 3,000 feet
Slope: Total range: 0 to 30 percent
Central tendency: 0 to 5 percent
Aspect: Occurs on all aspects


Geology:

This MLRA is almost entirely underlain by Miocene basalt flows. Columbia River basalt is covered in many areas with as much as 200 feet of loess and volcanic ash. Small areas of sandstones, siltstones, and conglomerates of the Upper Tertiary Ellensburg Formation are along the western edge of this area. Some Quaternary glacial drift covers the northern edge of the basalt flows, and some Miocene-Pliocene continental sedimentary deposits occur south of the Columbia River, in Oregon.

A wide expanse of scablands in the eastern portion of this MLRA, in Washington, was deeply dissected about 16,000 years ago, when an ice dam that formed ancient glacial Lake Missoula was breached several times, creating catastrophic floods. The geology of the northernmost part of this MLRA is distinctly different from that of the rest of the area. Alluvium, glacial outwash, and glacial drift fill the valley floor of the Okanogan River and the side valleys of tributary streams. The fault parallel with the valley separates pre-Tertiary metamorphic rocks on the west, in the Cascades, from older, pre-Cretaceous metamorphic rocks on the east, in the Northern Rocky Mountains. Mesozoic and Paleozoic sedimentary rocks cover the metamorphic rocks for most of the length of the valley on the west.

Climate

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 either xeric (12 – 16 inches PPT) or aridic moisture regimes (10 – 12 inches PPT) with a mesic temperature regime.

Mean Annual Precipitation:
Range: 10 – 16 inches
Seventy to seventy-five percent of the precipitation comes late October through March as a mixture of rain and snow. June through early October is mostly dry.

Mean Annual Air Temperature:
Range: 44 to 54 F
Central Tendency: 48 – 52 F
Freezing temperatures generally occur from late-October through early-April. Temperature extremes are 0 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: 90 to 200
Central tendency: 110 to 160
The growing season for loamy bottom is March through end of July.

Soil features

Edaphic:

The soils are deep, well drained, formed in loess, alluvium and unrestricted for plant growth. The soils are silt loam or sandy loam texture and are not saline or sodic, and not hydric. Loamy Bottom commonly occurs adjacent to Alkali Terrace, Sodic Flat, Wet Meadow Herbaceous Wetland and Riparian Woodland, ecological sites. It also occurs with upland sites such as Loamy, Stony, and Cool Loamy.


Representative Soil Features:

This ecological site components are dominantly Typic, Xeric, Torrifluventic and Pachic taxonomic subgroups of Haploxerolls, Endoaquolls and Argixerolls great groups of the Mollisols taxonomic order, with Aridisols occurring as well. Soils are dominantly deep or very deep but limited moderately deep occurs as well. Average available water capacity of about 5.0 inches (12.7 cm) in the 0 to 40 inches (0-100 cm) depth range.

Soil parent material is dominantly mixed alluvium and loess.

The associated soils are Benge, Brickmill, Cleman, Esquatzel, Hermiston, Kayak, Onyx, Weirman and similar soils.

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

Dominant particle-size class is fine to sandy-skeletal.

Fragments on surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 2

Fragments within surface horizon > 3 inches (% Volume):
Minimum: 0
Maximum: 30
Average: 5

Fragments within surface horizon ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 35
Average: 10

Subsurface fragments > 3 inches (% Volume):
Minimum: 0
Maximum: 25
Average: 5

Subsurface fragments ≤ 3 inches (% Volume):
Minimum: 0
Maximum: 45
Average: 10

Drainage Class: Range from somewhat poorly drained to well drained.
Water table depth: 20 to greater than 60 inches

Flooding:
Frequency: None to occasional

Ponding:
Frequency: None

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

Depth to root-restricting feature (inches):
Minimum: 40
Maximum: greater than 60

Electrical Conductivity (dS/m):
Minimum: 0
Maximum: 5

Sodium Absorption Ratio:
Minimum: 0
Maximum: 5

Calcium Carbonate Equivalent (percent):
Minimum: 0
Maximum: 30

Soil Reaction (pH) (1:1 Water):
0 - 10 inches: 5.1 to 9
10 - 40 inches: 5.6 to 9

Available Water Capacity (inches, 0 – 40 inches depth):
Minimum: 0.8
Maximum: 9.7
Average: 5.0

Vegetation dynamics

Ecological Dynamics:

Loamy Bottom produces about 4000 pounds/acre of biomass annually.

Loamy Bottom has several variations with basin wildrye as the constant:
1. Basin wildrye – sagebrush (basin, Wyoming)
2. Basin wildrye – three-tip sage (Douglas and Okanogan Co.)
3. Basin wildrye with no shrub in grassland areas in MLRA 8 (a little rabbitbrush)
4. Basin wildrye – rose

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 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. On a good Loamy Bottom site, basin wildrye, given good plant vigor, can take ownership even with invasive species in the community.

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.

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 topgrowth: (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 8, including Alkali Terrace, Sodic Flat, Wet Meadow, Wetland Complex and Riparian Complex. Loamy Bottom is also associated with upland sites such as Loamy, Stony, Very Shallow and Cool Loamy.

Similar Sites:
MLRAs 7 Columbia Basin and MLRA 9 Palouse Prairie 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 008X
Columbia Plateau

Subclasses

• R008XY930WA–Loamy Bottom

Stage

Provisional

Contributors

Provisional Site Author: Kevin Guinn

Technical Team: K. Moseley, G. Fults, R. Fleenor, W. Keller, K. Bomberger, C. Gaines, K. Paup-Lefferts