Natural Resources
Conservation Service

Ecological site R034BY011UT

River Flood Plain (Fremont Cottonwood)

Last updated: 3/05/2022
Accessed: 05/26/2026

Home / esd CATALOG / MLRA 034B / ecological site R034BY011UT

USC

Metric

General information

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.

Click to explore map

Figure 1. Mapped extent

Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.

MLRA notes

Major Land Resource Area (MLRA): 034B–Warm Central Desertic Basins and Plateaus

MLRA 34B occurs in is in Utah (70 percent) and Colorado (30 percent). It makes up about 12,850 square miles (33,290 square kilometers). A small part of the area is in the High Plateaus of Utah Section of the Colorado Plateaus Province of the Intermontane Plateaus. The northern part of the MLRA occurs in the Uinta Basin Section, which is bounded by the Uinta Mountains to the north, the Wasatch Range to the west, the Roan Plateau to the south, and the Rabbit Hills to the east. The southern part of the MLRA occurs in the northern third of the Canyon Lands Section. This section is bounded by the Roan Plateau to the north, the Wasatch Plateau to the west, the southern end of the San Rafael Swell to the south, and the western slope of the Rocky Mountains to the east. Elevation ranges from 4,100 feet (1,250 meters) near Green River, Utah, to 7,500 feet (2,285 meters) at the base of the Wasatch Range and the Roan Plateau.

Most of this area is covered by residual basin-floor materials and materials washed in from the surrounding mountains and plateaus. Shale and sandstone are the dominant rock types. The Tertiary-age Green River, Uinta, and Duchesne Formations dominate the northern part of the MLRA. The southern part is dominated by Cretaceous-age materials with lesser amounts of Jurassic and Triassic materials. The dominant Cretaceous formations are Mancos Shale, Dakota Sandstone, and the members of the Mesa Verde Group. The dominant Jurassic formations are the Morrison, Entrada, and Navajo. The dominant Triassic formations are the Chinle and Moenkopi. Quaternary alluvial, eolian, and glacial deposits occur in both parts of the MLRA.

The average annual precipitation in most of this area ranges from 6 to 10 inches (150 to 255 millimeters). A small part of this area receives as much as 24 inches of annual precipitation.
Much of the precipitation occurs as high-intensity, convective thunderstorms during the period July through September. May and June are usually the drier months. Precipitation is more evenly distributed throughout the year in the northern part of the MLRA than in the southern part, where there is a significant peak in late summer. The northern part of the MLRA receives more precipitation as snow during winter than the southern part. The average annual temperature ranges from 41 to 54 degrees F (5 to 12 degrees C). The freeze-free period averages 170 days and ranges from 110 to 235 days.

The dominant soil orders in this MLRA are Aridisols and Entisols. Mollisols occur at the higher elevations, particularly in the northern part of the MLRA. The dominant soil temperature regime is mesic, and the dominant soil moisture regime is aridic. The soils receiving less than 8 inches (205 millimeters) of precipitation annually have an aridic soil moisture regime. The soils receiving 8 to 12 inches (205 to 305 millimeters) have an aridic soil moisture regime that borders on ustic. The soils receiving 12 to 16 inches (305 to 405 millimeters) generally have an ustic soil moisture regime that borders on aridic. The dominant soil mineralogy is mixed and soils are formed in slope alluvium or residuum derived from shale or sandstone. Many of the soils are shallow or moderately deep to shale or sandstone bedrock. The soils at the lower elevations generally have significant amounts of calcium carbonate, salts, and gypsum.

Ecological site concept

This site occurs on flood plains of large, meandering rivers slopes are mostly 0 to 2 percent. Elevations range from 4700 to 5800 feet. Characteristic soils in this site are deep and moderately well drained. They formed in mixed alluvium derived mainly from sedimentary parent materials. Soils are flooded during high runoff and may be affected by a fluctuating water table during parts of the plant growing period. The water supplying capacity is 3 to 4 inches. Average annual soil loss in potential is approximately 1 ton per acre. Soil moisture regime is typic aridic to ustic aridic and soil temperature regime is mesic. Annual precipitation ranges from 5-12 inches annually.

Table 1. Dominant plant species

Tree	(1) Populus fremontii
Shrub	Not specified
Herbaceous	(1) Poa nevadensis (2) Elymus trachycaulus

Download full description

Physiographic features

This site occurs on flood plains of large, meandering rivers slopes are mostly 0 to 2 percent. Elevations range from 4700 to 5800 feet.

Table 2. Representative physiographic features

Landforms	(1) Flood plain (2)
Runoff class	Very low
Flooding duration	Brief (2 to 7 days)
Flooding frequency	None to rare
Elevation	4700 – 5800 ft
Slope	0 – 2 %
Ponding depth	0 in
Water table depth	24 – 48 in
Aspect	W, NW, N, NE, E, SE, S, SW

Climatic features

Average annual precipitation is 5 to 12 inches. Approximately 55 percent occurs as rain from march through may. On the average, June through October are the driest months and march through may are the wettest months. This site is flooded during high flows by the river it is associated with. In average years, plants begin growth around march 1 and end growth around October 15.

Table 3 Representative climatic features

Frost-free period (characteristic range)
Freeze-free period (characteristic range)	110-140 days
Precipitation total (characteristic range)	10-10 in

Soil features

Characteristic soils in this site are deep and moderately well drained. They formed in mixed alluvium derived mainly from sedimentary parent materials. The water supplying capacity is 3 to 4 inches. Average annual soil loss in potential is approximately 1 ton per acre. Soil moisture regime is typic aridic to ustic aridic and soil temperature regime is mesic. Annual precipitation ranges from 5-12 inches annually.

Table 4. Representative soil features

Parent material	(1) Alluvium – sedimentary rock
Surface texture	(1) Fine sandy loam
Family particle size	(1) Coarse-loamy
Drainage class	Moderately well drained
Permeability class	Moderate
Depth to restrictive layer	60 in
Soil depth	60 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (Depth not specified)	3 – 4 in
Calcium carbonate equivalent (Depth not specified)	2 – 10 %
Electrical conductivity (Depth not specified)	2 – 4 mmhos/cm
Sodium adsorption ratio (Depth not specified)	5 – 10
Soil reaction (1:1 water) (Depth not specified)	7.9 – 9
Subsurface fragment volume <=3" (Depth not specified)	2 %
Subsurface fragment volume >3" (Depth not specified)	Not specified

Ecological dynamics

Community Phase 1.1: Reference State
The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. The description of the Reference State was determined by NRCS Soil Survey Type Site Location information and familiarity with rangeland relict areas where they exist. The Reference State would have been in any of three phases depending on stream gradient and how recently fire had occurred or when beavers had last been present. Along steeper stream gradients, succession would have rapidly proceeded from low-statured graminoids (1.1), to shrubs (1.2), and lastly to trees that reproduce in their own shade (1.3). A complete list of species by lifeform for the Reference State is available in accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this document. Along gentle gradients beavers would have consumed all the largely deciduous woody stems and constructed dams. Once the nearby food and building materials were exhausted, the colony of beavers would have moved to another reach of the stream, making the abandoned dams and depleted stretch vulnerable to blow out from the next large convectional storm. This phase is short since most of the woody species re-sprout and are dominant again within a decade or so.

The resulting drop in the water table would have stressed the moisture-demanding woody species and favored the graminoids, allowing the graminoids to eventually reclaim the drier streamside banks. Thus, rather than one plant community becoming stable, these stretches of stream would have been in a continual state of change. Fur trapping in the 1820s-1830s resulted in the reduction of beaver by about 95% . Without these animals to maintain their stair-step configuration of dams, the whole hydrologic regime of these drainages changed. What were once small perennial streams became ephemeral, and succession was truncated. Beaver have not returned in number until recent decades (when the fur trade diminished and furbearers began to be raised on farms). Thus, by the time of the European settlement period, huge changes in these systems had already taken place.

Community Phase 1.1: graminoid dominance (rushes & sedges)
This early seral phase would have been dominated by rushes (Juncus spp.). Heavy local utilization by browsers or beaver would have kept back the woody species, allowing this graminoid phase to persist.

Community Pathway 1.1a:
Along gentler stream gradients, ponding caused by construction of beaver dams would have brought the water table up in areas that would have otherwise been dry. Heavy grazing by bison and/or elk would have reduced the graminoids, giving way first to some taller forbs. The same successional process would have taken place along steeper gradients, but at a more rapid rate.

Community Phase 1.2: mesic shrub dominance
A set of mesic shrubs including willow and/or basin big sagebrush would have quickly overtopped the graminoids, unless shrubs were cropped by moose or beaver.

Community Pathway 1.2a:
The presence of cottonwood seeds being carried by water would have provided for the rapid succession from shrubs to a gallery forest.

Community Pathway 1.2b:
As the supply of palatable deciduous shrubs and trees increased, beaver numbers would also have increased. With time, a heavy concentration of beaver and moose would have reduced the woody component, with the exception of the less palatable shrubs causing the canopy to open up.

Community Phase 1.3: gallery forest
Without beaver, tree cutting, and/or fire, a thick streamside (gallery) forest dominated by shade-tolerant cottonwood would have developed.

Community Pathway 1.3a:
A strong convectional storm associated with flash flooding would have blown out existing beaver dams. Unless the beavers were still occupying the area and rebuilt their dams, the water table would have eventually returned to previously lower levels. This would have allowed the graminoids to reclaim the site. Wildfire would have had a similar effect by removing most of the woody vegetation and debris, thereby re-opening the site to graminoids.

Community Pathway 1.3b:
This community pathway would be similar to 1.2b, except less intense. Flash flooding may blow out existing beaver dams following convectional storm events, but some smaller-statured trees and shrubs would persist, leaving enough woody material such that beavers could subsist and rebuild their dams.

Transition T1a: from State 1 to State 2 (Reference State to Xerified Shrub and Tree Dominated Drained State)
The simultaneous introduction of European livestock and exotic plant species, the near extirpation of beaver along with its influence on the hydrologic regime, and a warmer drier climate were all factors involved in the transition to State 2. A return to State 1 would not be impractical because of these issues.

Community Phase 2.2: Xerified Shrub and Tree Dominated Drained State
State 2 is similar to State 1 in form and function, with the exception of the presence of non-native plants and animals, possible extinctions, and a different climate. State 2 is a description of the ecological site shortly following Euro-American settlement. This state can be regarded as the current potential. Depending on the size of the watershed above, the stream could well have changed from a perennial to ephemeral drainage. Many of the same species of plants found in the Reference State continue to exist in the latter situation because of hyporheic (i.e. below ground) movement of water, although the period of greenery and its productivity are lessened. The introduction of cattle put pressure on the graminoids (2.1a) and hastened the conversion to shrubs (2.2). The lack of beaver dams meant that sediment moved more rapidly downstream with flashy (short duration, high intensity) precipitation events. Stream channelization occurred with increased rates of flow, leading to xerification of the streamside. With beaver temporarily absent, livestock numbers relatively reduced due to lack of forage, and lack of natural disturbances (2.2a), the shrubs and trees grow larger and shade out many of the forage species favored by livestock (2.3). The most disturbed phase of this State would be the graminoid-dominant phase (2.1), which occurs if moose effectively browse out the shrubby vegetation (2.2b). Kentucky bluegrass (Poa pratensis) was introduced at some sites for livestock forage; however it is not capable of holding the stream banks together during convectional storms.

Community Phase 2.1: graminoid dominance
This graminoid-dominated phase is frequently dominated by Kentucky bluegrass. The Forest Service regards this as an introduced species, but it is preferred by livestock over other native graminoids. It is, however, less able to protect stream banks than its native counterparts because of its shallower, weaker roots.

Community Pathway 2.1a:
Heavy season-long use by cattle will diminish the grass component and allow an increase in tall forbs. Sheep will consume most of the forbs and shrubs, but will leave the less palatable ones.

Community Phase 2.2: mesic shrub dominance
This plant community will be dominated by unpalatable mesic shrubs with an understory of unpalatable herbs including thistles and horsetail. Species composition will depend upon the type of livestock utilizing the area.

Community Pathway 2.2a:
Without sheep and/or beaver consumption of shrubs and sapling trees, the shrub phase quickly transforms to a gallery forest.

Community Pathway 2.2b:
Browsing of palatable woody species will cause a retardation of the shift to shrub and tree dominance.

Community Phase 2.3: gallery forest
This plant community is dominated by cottonwood, a shade-tolerant species, which will persist in the absence of wildfire, wood cutting, and/or large storm events.

Community Pathway 2.3a:
A gallery forest can persist in the absence of fire or wood cutting, creating a jack-strawing of downed trees that will make access to the site difficult for large animals.

Transition T2a: from State 2 to State 3 (Xerified Shrub and Tree Dominated Drained State to Improved Pasture State)
Since there is diminished forage production in the woody plant-dominated phases of State 2, some private landholders have, through prescribed fire and mechanical treatments, cleared out the streamside vegetation and planted exotic species such as smooth brome or crested wheatgrass to replace the native species.

State 3: Improved Pasture State

Community Phase 3.3: Improved Pasture State
Some private land owners have bulldozed the streamside vegetation to remove trees needed by beavers to pond up the stream and/or to remove shade to increase forage production for livestock. Introduced species such as crested wheatgrass and smooth brome have been planted as the site became xerified, but more conducive to cattle grazing. The early seral vegetation created constitutes Phase 3.1. With time and heavy cattle grazing (3.1a), the tendency is for the original shrubs and trees to return (3.2). If introduced grass dominance is desired, mechanical or chemical retreatment to reduce the woody plants will be required (3.2a).

Community Phase 3.1: planted pasture
This plant community will be dominated by introduced species such as crested wheatgrass and smooth brome.

Community Pathway 3.1a:
In order to maintain an herbaceous-dominant phase, the native woody species may require re-treatment using mechanical or chemical means.

Community Phase 3.2: woody encroachment
This plant community will be a mix of introduced grasses and native shrubs that have re-established following a period of heavy continuous season-long grazing.

Community Pathway 3.2a:
Some re-establishment of native shrubs will occur if the site is heavily grazed during the growing season of the grasses.

State and transition model

Custom diagram

Standard diagram

More interactive model formats are also available. View Interactive Models

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Reference State

State 1 submodel, plant communities

1.1. Reference State

State 1
Reference State

Community 1.1
Reference State

The dominant aspect of the plant community is an open savannah of cottonwood with an understory of willows and grass. The composition by air-dry weight is approximately 45 percent perennial grasses, 10 percent forbs, and 45 percent shrubs.

Figure 2. Annual production by plant type (representative values) or group (midpoint values)

Table 5. Annual production by plant type

Plant type	Low (lb/acre)	Representative value (lb/acre)	High (lb/acre)
Shrub/Vine	535	587	658
Grass/Grasslike	535	587	658
Forb	120	134	154
Tree	10	42	80
Total	1200	1350	1550

Table 6. Ground cover

Tree foliar cover	10-20%
Shrub/vine/liana foliar cover	20-20%
Grass/grasslike foliar cover	40-40%
Forb foliar cover	0-10%
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 7. Canopy structure (% cover)

Height Above Ground (ft)	Tree	Shrub/Vine	Grass/ Grasslike	Forb
<0.5	–	–	–	–
>0.5 <= 1	–	–	–	4-6%
>1 <= 2	–	–	39-41%	–
>2 <= 4.5	–	19-21%	–	–
>4.5 <= 13	–	–	–	–
>13 <= 40	–	–	–	–
>40 <= 80	14-16%	–	–	–
>80 <= 120	–	–	–	–
>120	–	–	–	–

Additional community tables

Table 8. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)
Tree
0	Dominant Trees			14–70
	Fremont cottonwood	POFR2	Populus fremontii	14–70	–
Shrub/Vine
0	Dominant Shrubs			280–490
	narrowleaf willow	SAEX	Salix exigua	140–210	–
	basin big sagebrush	ARTRT	Artemisia tridentata ssp. tridentata	70–140	–
	rubber rabbitbrush	ERNA10	Ericameria nauseosa	70–140	–
3	Sub-Dominant			140–330
	Shrub (>.5m)	2SHRUB	Shrub (>.5m)	70–140	–
	yellow rabbitbrush	CHVI8	Chrysothamnus viscidiflorus	14–42	–
	skunkbush sumac	RHTRT	Rhus trilobata var. trilobata	14–42	–
	golden currant	RIAU	Ribes aureum	14–42	–
	greasewood	SAVE4	Sarcobatus vermiculatus	14–42	–
Grass/Grasslike
0	Dominant Grasses			438–700
	slender wheatgrass	ELTR7	Elymus trachycaulus	210–280	–
	Sandberg bluegrass	POSE	Poa secunda	210–280	–
	western wheatgrass	PASM	Pascopyrum smithii	14–70	–
	saltgrass	DISP	Distichlis spicata	14–70	–
1	Sub-Dominant Grasses			140–308
	Grass, annual	2GA	Grass, annual	42–70	–
	Grass, perennial	2GP	Grass, perennial	42–70	–
	squirreltail	ELEL5	Elymus elymoides	14–42	–
	meadow barley	HOBR2	Hordeum brachyantherum	14–42	–
	mountain rush	JUARL	Juncus arcticus ssp. littoralis	14–42	–
	alkali sacaton	SPAI	Sporobolus airoides	14–42	–
Forb
2	Sub-Dominant			462–910
	Forb, annual	2FA	Forb, annual	140–210	–
	Forb, perennial	2FP	Forb, perennial	140–210	–
	Fremont's goosefoot	CHFR3	Chenopodium fremontii	14–42	–
	narrowleaf goosefoot	CHLE4	Chenopodium leptophyllum	14–42	–
	Rocky Mountain beeplant	CLSE	Cleome serrulata	14–42	–
	western tansymustard	DEPI	Descurainia pinnata	14–42	–
	curlycup gumweed	GRSQ	Grindelia squarrosa	14–42	–
	povertyweed	IVAX	Iva axillaris	14–42	–
	mountain pepperweed	LEMO2	Lepidium montanum	14–42	–

Interpretations

Animal community

This site provides proper grazing for cattle and sheep during all seasons of the year.

This site provides food and cover for wildlife. Wildlife using this site include jackrabbit, coyote, kangaroo rat, snake, hawk, and mule deer.

Hydrological functions

The soil is in hydrologic group B. The runoff curve numbers are 61 through 79 depending on the condition of the watershed

Recreational uses

Recreation activities are hiking and hunting.

Wood products

Firewood

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)	V. Keith Wadman, NRCS Retired.
Contact for lead author	shane.green@ut.usda.gov
Date	05/23/2012
Approved by
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Rill occurrance is highly variable. This site is subject to frequent disturbance caused by seasonal flooding with its' associated soil scouring and deposition activities. Where rills are present they should be less than 1 inch deep, somewhat widely spaced (10 to 15 feet), and may be connected. They will often run the length of the streambank to a point of depositional interruption. An increase in rill development may be observed following large storm events or spring runoff periods. Rill development may also increase where the site is adjacent to other sites that produce large amounts of runoff (i.e. steeper sites, slickrock, etc.)
Presence of water flow patterns:
Water flow patterns are common. They may be stright and/or sinuous and wind around perennial plant bases. They may be long (15 to 25 feet), 1 to 3 feet wide, and spaced from 5 to 20 feet apart. They should become somewhat stable between flooding events. This site will often act as a soil filter and trap large amounts of sediment. These become ideal locations for the establishment of new riparian vegetation.
Number and height of erosional pedestals or terracettes:
Plants are expected to show some pedestalling where they are adjacent to water flow patterns. Exposed roots may be present where scouring has occurred. Terracettes are also typically present following flooding events. They often develop behind debris such as twigs and tree branches that act as dams within water flow patterns.
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground is variable on this site, but should range from 25 to 40%. Bare ground openings should be approximately 1 to 3 feet in size and may be connected as flow channels. Adapted rhizomatous riparian vegetation will often re-populate these opening between flood events.
Number of gullies and erosion associated with gullies:
None at site level. Widely scattered landscape level gully channels, however, are a normal component of desert environments. Where landscape gullies are present, they should be stable, partially vegetated on their sides and bottoms, with little evidence of head-cutting. Some slight increase in disturbance may be evident following significant weather events or when gullies convey considerable runoff from higher elevation rocky or naturally eroding areas.
Extent of wind scoured, blowouts and/or depositional areas:
No evidence of wind generated soil movement. Wind caused blowouts and depositional areas are not present.
Amount of litter movement (describe size and distance expected to travel):
Litter accumulates in place at the base of plant canopies between flood events. Following significant flood events, litter is expected to be transported downstream by water. Considerable accumulation is observed behind obstructions such as rocks and woody debris.
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
This sites soil stability rating is highly variable. A rating of 3 to 5 should occur on areas with stable soils, with a rating of 1 to 4 on depositional materials. The average should be in the 2 to 4 range. Surface textures will typically vary from sands and gravels in depositional areas to sandy loams, loams and clay loams on stable soils.
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
(Colorow) Soil surface is typically 0 to 5 inches deep. Surface texture is a sandy loam and structure is moderate and strong very thin, thin and medium platy. The A-horizon color is pale brown (10YR 6/3). Soils have an Ochric epipedon that extends 5 inches into the soil profile. The A horizon is normally deeper and better developed on the more stable portions of the streambank. Use the specific information for the soil you are assessing found in the published soil survey to supplement this description.
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Perennial vegetation helps anchor streambanks, reducing soil scouring and increasing deposition. Good spatial distribution of plants also slows runoff by obstructing surface flows, allowing time for increased infiltration. With the physiographic location of this site being in low lying areas, it often acts as a terminal accumulation site for runoff.
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None. This site will normally have textural variation within its' soil profile. These should not be mistaken for compaction layers.
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):

Dominant:
Trees (Fremont cottonwood) > Sprouting Shrubs (Coyote willow, rubber rabbitbrush) >> Perennial Grasses (slender wheatgrass, Nevada bluegrass) > Perennial grasslikes (arctic rush, scouring rush) > Perennial Forbs (Rocky mountain beeplant).

Sub-dominant:
Non-sprouting Shrubs (basin big sagebrush) > Rhizomatous Grasses (Alkali sacaton, western wheatgrass) >> Perennial Forbs (narrowleaf goosefoot).

Other:
Functional/structural groups may appropriately contain non-native species if their ecological function is the same as the native species in the reference state. Biological soil crust is variable in its' expression where present on this site and is measured as a component of ground cover. Perennial and annual forbs can be expected to vary widely in their expression in the plant community based upon departures from average growing conditions.

Additional:
Disturbance regimes include seasonal flooding, insects, and infrequent fire. Temporal variability can be caused by fires, droughts, insects, etc. Spatial variability can be caused by runoff, soil pH, and topography. Fremont cottonwood is very sensitive to fire and may be replaced by other, more fire tolerant woody species such as narrowleaf cottonwood, with repeated fire. Following a recent disturbance such as drought, or flooding damage that removes woody vegetation, forbs and perennial grasses and grasslikes may dominate the community. If a disturbance has not occurred for an extended period of time, woody species may continue to increase on the site, reducing herbaceous species. Yearly variations in flow and large floods that scour vegetation and deposit sediment on floodplains are ideal microsites for willow and cottonwood seeds. These conditions may reflect community phases within the reference state.
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
There should be no mortality or decadence in either trees, shrubs or grasses during years with average to above average precipitation. During severe (multi-year) droughts that affect groundwater levels, up to 15% of the trees and shrubs may die. Minor mortality of perennial grasses and grasslikes may also occur during these drought periods. There may be partial mortality of individual grasses, grasslikes and shrubs during less severe droughts.
Average percent litter cover (%) and depth ( in):
Litter cover is highly variable on this site and ranges from 15 to 30%. Depth should be 1/2 inch thickness in the interspaces and up to 2.5 inches under perennial plant canopies.
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Annual production in air-dry herbage should be approximately 1300 to 1400 pounds per acre on an average year. Production could vary from 1150 to 1600 pounds per acre during drought or above-average years.
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
Tamarisk, knapweed species, Russian thistle, mustard species, filarie, other non-native annual forbs and grasses.
Perennial plant reproductive capability:
All perennial plants should have the ability to reproduce sexually or asexually in most years, except in drought years. Rhizomatous plants including rushes and sedges are often the first to re-establish following flooding, coyote willow and Fremont cottonwood seedlings and saplings should also be present.

Download reference sheet

Natural ResourcesConservation Service