Natural Resources
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Ecological site R028AY418UT
Mountain Loam (Bigtooth Maple)
Last updated: 5/02/2025
Accessed: 07/12/2026
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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.
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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): 028A–Ancient Lake Bonneville
MLRA 28A occurs in Utah (82 percent), Nevada (16 percent), and Idaho (2 percent). It encompasses approximately 36,775 square miles (95,246 square kilometers). A large area west and southwest of Great Salt Lake is a salty playa. This area is the farthest eastern extent of the Great Basin Section of the Basin and Range Province of the Intermontane Plateaus. It is an area of nearly level basins between widely separated mountain ranges trending north to south. The basins are bordered by long, gently sloping alluvial fans. The mountains are uplifted fault blocks with steep side slopes. Most of the valleys are closed basins containing sinks or playa lakes. Elevation ranges from 3,950 to 6,560 feet (1,204 to 2,000 meters) in the basins and from 6,560 to 11,150 feet (1,996 to 3,398 meters) in the mountains. Much of the MLRA has alluvial valley fill and playa lakebed deposits at the surface from pluvial Lake Bonneville, which dominated this MLRA 13,000 years ago. A level line of remnant lake terraces on some mountain slopes indicates the former extent of this glacial lake. The Great Salt Lake is what remains of the pluvial lake.
Mountains in the interior of this MLRA consist of tilted blocks of marine sediments from Cambrian to Mississippian age with scattered outcrops of Tertiary continental sediments and volcanic rocks. The average annual precipitation is 5 to 12 inches (13 to 30 cm) in the valleys and ranges up to 49 inches (124 cm) in the mountains. Most of the rainfall in the southern LRU occurs as high-intensity, convective thunderstorms during the growing season (April through September). The driest period is from midsummer to early autumn in the northern LRU. Precipitation in winter typically occurs as snow. The average annual temperature is 39 to 53 °F (4 to 12 °C). The freeze-free period averages 165 days and ranges from 110 to 215 days, decreasing in length with increasing elevation. The dominant soil orders in this MLRA are Aridisols, Entisols, and Mollisols. Soils are dominantly in the mesic or frigid soil temperature regime, aridic or xeric soil moisture regime, and mixed mineralogy. The soils are generally well drained, loamy or loamy-skeletal, and very deep.LRU notes
The Basin and Range North LRU exhibits dry summer with stronger xeric patterns than the Basin and Range South LRU. Ranges in the north LRU are about 50 percent Paleozoic sedimentary/metasedimentary (limestone/quartzite dominant) and about 10 percent Tertiary volcanics. The basin floors are between 4,200 and 5,100 feet (1,280 to 1,554 meters) in elevation. Pinyon and juniper sites have a greater percentage of Utah juniper (Juniperus osteosperma) in the plant community than pinyon pine (Pinus edulis or monophylla). The Basin and Range North have few semidesert ecological sites with Utah juniper. Cool-season grasses, such as bluebunch wheatgrass (Pseudoroegneria spicata), are dominant in the plant community, while warm-season grasses are largely absent or a small component of the plant community.
Ecological site concept
The Mountain Loam (Bigtooth Maple) site is located on steep mountain slopes (30 to 70 percent) between 6,300 and 8,000 feet (1,920 to 2,438 meters). The soil is clayey-skeletal and deep. The precipitation ranges from 17 to 31 inches (432 to 787 mm). The dominant vegetation is bigtooth maple (Acer grandidentatum), mountain big sagebrush (Artemisia tridentata ssp. vaseyana), and bluebunch wheatgrass (Pseudoroegneria spicata). Total canopy cover in the Reference State is about 10 percent grasses, 10 percent forbs, 10 percent shrubs, and 20 percent trees.
Associated sites
R028AY324UT Upland Shallow Loam (Utah Juniper - Singleleaf Pinyon)
This site will occur in convex positions in shallow soils.
Similar sites
R047XA418UT Mountain Loam (bigtooth maple)
This site is mapped in both MLRA 28A and MLRA 47A and has been used interchangeably.
Table 1. Dominant plant species
Tree (1) Acer grandidentatum
Shrub Not specified
Herbaceous Not specified
Physiographic features
The Mountain Loam (Bigtooth Maple) site occurs in drainages on the steep west facing mountain slopes at lower elevations and north and west facing mountain slopes at steep upper elevations. Slopes are typically between 30 and 70 percent. This site is found at elevations between 6,300 and 8,000 feet (1,920 to 2,438 meters). Flooding does not occur on this site.
Table 2. Representative physiographic features
Landforms (1) Mountain slope
Flooding frequency None Ponding frequency None Elevation 6300 – 8000 ft Slope 30 – 70 % Aspect W, NW Climatic features
The climate is characterized by warm, dry summers, cold, snowy winters and moist springs. The average annual precipitation is between 17 and 31 inches. October through May is the wettest part of the year and June through August are the driest. The effective moisture for plant growth is the portion that falls during the plant dormant period, which wets the soil deeply in the spring.
Table 3 Representative climatic features
Frost-free period (characteristic range) Freeze-free period (characteristic range) Precipitation total (characteristic range) 20-30 in Frost-free period (average) Freeze-free period (average) 110 days Precipitation total (average) 20 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Due to its landscape position, the Mountain Loam (Bigtooth Maple) site is not typically influenced by streams or wetlands. It may be influenced by overland flow during heavy thunderstorms and/or during wetter spring runoff periods.
Soil features
The characteristic soils are greater than 60 inches deep and well drained. The soil was formed in colluvium derived from limestone, sandstone, shale and/or quartzite. The surface horizon has a loam texture. Rock fragments occur infrequently on the soil surface and make up less than 15 percent of the soil cover and less than 40 percent of the subsoil volume. Available water capacity ranges from 4 to 5 inches in the upper 40 inches of soil. These soils are neutral and are not calcareous on the surface. The soil moisture regime is xeric and the soil temperature regime is frigid.
Soil Map Units that may contain this site:
Soil Survey Area: Soil Components (Map units in parentheses)
Fairfield-Nephi Area (UT608): Hamtah (HaF)Table 4. Representative soil features
Parent material (1) Colluvium – limestone and sandstone
Surface texture (1) Loam
Drainage class Well drained Permeability class Slow Surface fragment cover <=3" 11 – 0 % Surface fragment cover >3" 3 – 0 % Available water capacity
(Depth not specified)4.1 – 5.4 in Subsurface fragment volume <=3"
(Depth not specified)22 – 0 % Subsurface fragment volume >3"
(Depth not specified)18 – 0 % Ecological dynamics
The Mountain Loam (Bigtooth Maple) site is found in the Great Salt Lake Area of the Basin and Range Ecological Provence. It developed under the natural ecological conditions found there, including the normal influences of native wildlife herbivory, fire and climate. Bigtooth maple dominates the tree canopy and mountain big sagebrush dominates the shrub layer. A mix of other shrubs including snowberry and serviceberry are commonly found. Perennial herbaceous species occurrence and production is directly related to overstory canopy density with bluebunch wheatgrass and Great Basin wildrye (Leymus cinereus) found most often. This site can be invaded by annual grasses and forbs, but these species have only been documented with low cover and low production.
Bigtooth maple can be found in a variety of different site conditions. It is fairly drought-tolerant and can be found on drier slopes, but it is most often found in cooler drainages on north-facing slopes. The seedlings are shade-tolerant and can be found growing under the canopy of mountain big sagebrush. Fire frequency in this site is low and the bigtooth maple is generally fire tolerant. If fire occurs and the bigtooth maple stems are burned, the root crown may re-sprout. Sprouting is most likely to occur from younger plants growing on cooler more moist sites. This site historically would have been dominated by more grass that would have allowed more frequent fires which would have kept the maple cover low. Due to changes in management (i.e. fire suppression, livestock grazing) bigtooth maple has increased. If the trees mature, the stand becomes less susceptible to fire (Tollefson 2006).
Three possible stable states have been hypothesized for this ecological site. These plant communities may not represent every possibility, but they are the most prevalent and repeatable plant communities. As more data is collected, some of these plant communities may be revised or removed and new ones may be added. None of these plant communities should necessarily be thought of as the “desired plant community”. According to the USDA NRCS National Range and Pasture Handbook, the desired plant community will be determined by the decision makers and will meet minimum quality criteria established by the NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision. Specific community phases and transitions will be described in the narratives below.State and transition model
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Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 2 submodel, plant communities
State 3 submodel, plant communities
State 1
Reference StateThe Reference State is the least modified plant community that would have been dominated by bigtooth maple. Rocky Mountain juniper (Juniperus scopulorum) may also have been a common associate. The understory shrubs would have included mountain big sagebrush, antelope bitterbrush, and chokecherry (Prunus virginiana). Forbs would have included common yarrow (Achillea millefolium), arrowleaf balsamroot (Balsamorhiza sagittata), sticky purple geranium (Geranium viscosissimum), milkvetch (Astragalus spp.), and buckwheats (Eriogonum spp.), among others. Bluebunch wheatgrass, basin wildrye, and muttongrass (Poa fendleriana) would have been the dominant grasses.
Community 1.1
Scattered bigtooth maple/grass-forb-shrubsThis community is characterized by scattered bigtooth maple with a diverse understory of grasses, forbs and low shrubs. The composition by air-dry weight is approximately 40 percent perennial grasses, 30 percent shrubs, 25 percent trees and 5 to 10 percent forbs.
Figure 4. 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)Grass/Grasslike 560 860 1000 Shrub/Vine 420 645 750 Tree 350 538 625 Forb 140 215 250 Total 1470 2258 2625 Table 6. Ground cover
Tree foliar cover 20-20% Shrub/vine/liana foliar cover 10-10% Grass/grasslike foliar cover 10-10% Forb foliar cover 10-10% 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/
GrasslikeForb <0.5 – – – – >0.5 <= 1 – – – 5-15% >1 <= 2 – – 5-15% – >2 <= 4.5 – 5-15% – – >4.5 <= 13 – – – – >13 <= 40 15-25% – – – >40 <= 80 – – – – >80 <= 120 – – – – >120 – – – – Figure 5. Plant community growth curve (percent production by month). UT4182 , PNC. Excellent Condition.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 5 15 40 20 10 5 5 0 0 0 State 2
Thickened Bigtooth Maple and Low Shrubs StateState 2 occurred by the introduction of several non-native plants and animals, possible extinctions of native species, and a different climate. The plant community is very similar to State 1 with the exception that some introduced species are likely to be present. The herbaceous species still left in the understory are those more tolerant of grazing pressure and/or are relatively unpalatable to livestock such as Woods’ rose (Rosa woodsii) and mule-ears (Wyethia amplexicaulis). This state has potential of accelerated soil erosion. Where accelerated soil erosion has not yet occurred, the potential for stability in this state is high.
Community 2.1
Thickened Bigtooth Maple and Low Shrubs/Diminished Native Perennial HerbsThis community is characterized by thickened bigtooth maple and low shrubs, such as mountain big sagebrush, antelope bitterbrush, Woods’ rose, and chokecherry. While native perennial herbs have diminished, those remaining include arrowleaf balsamroot, common yarrow, and mules-ear.
State 3
Re-sprouting Shrubs/Introduced Non-natives StateThis state occurs following heavy, sustained grazing in conjunction with tree removal for firewood and fence-posts.
Community 3.1
Re-sprouting lower statured tall and low shrubs/ invasive understoryCommunity Phase 3.1 is characterized by re-sprouting shrubs, such as yellow rabbitbrush (Chrysothamnus viscidiflorus), rubber rabbitbrush (Ericameria nauseosa), and broom snakeweed (Gutierrezia sarothrae). Among the few native grasses are an abundance of non-native grasses such as cheatgrass.
Transition T1A
State 1 to 2The simultaneous introduction of exotic species, both plants and animals, possible extinctions of native flora and fauna, and climate change has caused State 1 to transition to State 2. The advent of heavy continuous season-long grazing by livestock and fire prevention also contributed to this transition. Reversal of such historic changes (i.e. a return pathway) back to State 1 is not practical.
Transition T2A
State 2 to 3Firewood harvest and/or wildfire will remove the trees while continued heavy livestock grazing during the growing season will further reduce the understory and open it up to introduced non-native species such as cheatgrass (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=BRTE" target="_blank" title="Open in plants.usda.gov"><i>Bromus tectorum</i></a>) and bulbous bluegrass (<a class="species-link" href="https://plants.usda.gov/core/profile?symbol=POBU" target="_blank" title="Open in plants.usda.gov"><i>Poa bulbosa</i></a>). A key indicator of the approach to this transition is the reduction of desirable forage and a loss of larger stems of maple. Sustained heavy grazing is the trigger for this transition.
Additional community tables
Table 8. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Shrub/Vine0 Primary Shrubs 308–550 mountain big sagebrush ARTRV Artemisia tridentata ssp. vaseyana 110–220 – yellow rabbitbrush CHVI8 Chrysothamnus viscidiflorus 66–110 – chokecherry PRVI Prunus virginiana 66–110 – mountain snowberry SYOR2 Symphoricarpos oreophilus 66–110 – 3 Secondary Shrubs 66 Saskatoon serviceberry AMAL2 Amelanchier alnifolia 22–66 – slender buckwheat ERMI4 Eriogonum microthecum 22–66 – Grass/Grasslike0 Primary Grasses 440–660 bluebunch wheatgrass PSSP6 Pseudoroegneria spicata 330–440 – basin wildrye LECI4 Leymus cinereus 110–220 – 1 Secondary Grasses 110–220 Geyer's sedge CAGE2 Carex geyeri 66–110 – slender wheatgrass ELTR7 Elymus trachycaulus 66–110 – slender wheatgrass ELTRS Elymus trachycaulus ssp. subsecundus 66–110 – prairie Junegrass KOMA Koeleria macrantha 66–110 – western wheatgrass PASM Pascopyrum smithii 66–110 – muttongrass POFE Poa fendleriana 66–110 – Kentucky bluegrass POPR Poa pratensis 66–110 – Sandberg bluegrass POSE Poa secunda 66–110 – Forb2 Forbs 110–220 common yarrow ACMI2 Achillea millefolium 22–66 – nettleleaf giant hyssop AGUR Agastache urticifolia 22–66 – arrowleaf balsamroot BASA3 Balsamorhiza sagittata 22–66 – tapertip hawksbeard CRAC2 Crepis acuminata 22–66 – Eaton's fleabane EREA Erigeron eatonii 22–66 – common motherwort LECA2 Leonurus cardiaca 22–66 – tailcup lupine LUCAC3 Lupinus caudatus ssp. caudatus 22–66 – Tree4 Trees 506–770 bigtooth maple ACGR3 Acer grandidentatum 440–660 – Rocky Mountain juniper JUSC2 Juniperus scopulorum 66–110 – Table 9. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
The Mountain Loam (Bigtooth Maple) site provides forage for cattle and sheep grazing during spring, summer, and fall.
Wildlife using this site include mule deer, elk, coyote, badger, fox, ruff grouse, mourning dove, and golden eagle.
This is a short list of the more common species found. Many other species are present as well and migratory birds are present at times.Hydrological functions
The hydrologic group is B. The hydrologic curve number is 61 when the vegetation is in good condition.
Recreational uses
Hiking and hunting.
Wood products
Firewood and fence dancers.
Other information
Threatened and endangered species include plants and animals.
Supporting information
Type locality
Location 1: Box Elder County, UT General legal description Found in Canyons West and South of Portage Contributors
G. Brock Benson
GBBApproval
Jamin Johanson, 5/02/2025
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) Jack Alexander, Range Specialist, Synergy Resource Solutions, Inc. Julia Kluck, Soil Scientist, Synergy Resource Solutions, Inc. Shane Green, State Range Specialist, Utah NRCS Contact for lead author Shane Green, Shane.Green@ut.usda.gov Date 02/09/2010 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
Very rare rills may be present. Rill development may increase following large storm events, but should begin to heal during the following growing season. Frost heaving will accelerate recovery. Rill development may increase when run inflow enters site from other sites that produce large amounts of runoff (i.e. steeper sites, slickrock, rock outcrop). -
Presence of water flow patterns:
Water flow patterns will be short (2-5’), narrow (<1’), and meandering; interrupted by plants and exposed rocks. Slight to no evidence of erosion or deposition associated with flow patterns. -
Number and height of erosional pedestals or terracettes:
Plants may have small pedestals (1”) where they are adjacent to water flow patterns, but without exposed roots. Terracettes should be few and stable. Terracettes should be small (3-6”) and show little sign of active erosion. Some plants may appear to have a pedestal but rather than be formed by erosion, the only place litter accumulates and soil collects is at plant bases forming the appearance of a pedestal. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
15-30% bare ground (soil with no protection from raindrop impact). Herbaceous communities are most likely to have lower values. As species composition by shrubs increases, bare ground is likely to increase. Poorly developed biological soil crust that is susceptible to raindrop splash erosion should be recorded as bare ground. Very few if any bare spaces of greater than 1 square foot. -
Number of gullies and erosion associated with gullies:
No gullies present. -
Extent of wind scoured, blowouts and/or depositional areas:
Very minor evidence of active wind-generated soil movement. Wind scoured (blowouts) and depositional areas are rarely present. If present they have muted features and are mostly stabilized with vegetation and/or biological crust. Gravel or desert pavement protects the site from wind scour. -
Amount of litter movement (describe size and distance expected to travel):
Most litter resides in place with some redistribution caused by water and wind movement. Very minor litter removal may occur in flow patterns and rills with deposition occurring at points of obstruction. The majority of litter accumulates at the base of plants. Some leaves, stems, and small twigs may accumulate in soil depressions adjacent to plants. Woody stems are not likely to move. On steep slopes (>30%), litter will move downhill to next obstruction. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
This site should have an erosion rating of 5 or 6 under plant canopies and a rating of 4 to 5 in the interspaces with an average rating of 5 using the soil stability kit test. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
This description is based on the soil (Hamtah), the only soil correlated with this site. Soil surface horizon is typically 21 inches deep. Structure is typically moderate find and medium subungular blocky. Color is typically dark grayish brown (10YR 4/2), very dark brown (10YR 2/2) moist. Mollic epipedon is common. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Vascular plants and any well-developed biological soil crusts (where present) will break raindrop impact and splash erosion. Spatial distribution of vascular plants and interspaces between well-developed biological soil crusts (where present) provide detention storage and surface roughness that slows runoff allowing time for infiltration. Crowns of trees and accumulating litter at base of trees appear to create a micro-topography that may enhance development of water flow patterns below the drip line of the canopy. Significant increases in pinyon-juniper canopy reduces understory vegetation and increases runoff. -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None. Naturally occurring soil horizons may be harder than the surface because of an accumulation of clay and should not be considered as 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 (bigtooth maple) > Cool season perennial bunchgrass, mid height (bluebunch wheatgrass)Sub-dominant:
Cool season perennial bunchgrass, tall (basin wildrye) > nonsprouting shrubs (mountain big sagebrush)Other:
other grasses > forbs > other shrubs, other treesAdditional:
Functional/structural groups may appropriately contain non-native species if their ecological function is the same as the native species in the reference state (e.g. crested wheatgrass and Russian wildrye may substitute for mid stature cool season perennial native bunchgrasses.). Biological soil crust is variable in its expression on this site and is measured as a component of ground cover. Forbs can be expected to vary widely in their expression in the plant community based upon departures from average growing conditions. -
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
During years with average to above average precipitation, there should be very little recent mortality or decadence apparent in either the shrubs or grasses. Some mortality of bunchgrass and other shrubs may occur during very severe (long-term) droughts. There may be partial mortality of individual bunchgrasses and shrubs during less severe drought. Long-lived species dominate site. Open spaces from disturbance are quickly filled by new plants through seedlings and reproductive reproduction (tillering). -
Average percent litter cover (%) and depth ( in):
Litter cover includes litter under plants. Most litter will be fine litter. Depth should be 1-2 leaf thickness in the interspaces and up to 1/2” under canopies. Litter cover may increase to 40-50% following years with favorable growing conditions. Excess litter may accumulate in absence of disturbance. Vegetative production may be reduced if litter cover exceeds 40%. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
2250#/acre. Even the most stable communities exhibit a range of production values. Production will vary between communities and across the MRLA. Refer to the community descriptions in the ESD. Production will differ across the MLRA due to the naturally occurring variability in weather, soils, and aspect. The biological processes on this site are complex; therefore, representative values are presented in a land management context. -
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:
Cheatgrass, annual sunflower, and flannel mullein -
Perennial plant reproductive capability:
All perennial plants should have the ability to reproduce sexually or asexually, except in drought years. Density of plants indicates that plants reproduce at level sufficient to fill available resource. Within capability of site there are no restrictions on seed or vegetative reproductive capacity.
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