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.
Ecological site concept
This site occurs on summits of fan remnants. Slopes gradients of 2 to 15 percent but slopes of 2 to 8 percent are most typical. Elevations are 800 to about 4700 feet.
A continuous desert pavement of at least 80 percent gravels covers the soil surface. Surface rock fragments are coated with a shiny patina (desert varnish) on the exposed surfaces. The rock fragments tend to be imbedded, leaving a smooth soil surface.
This site occurs on summits of fan remnants. Slopes gradients of 2 to 15 percent but slopes of 2 to 8 percent are most typical. Elevations are 800 to about 4700 feet.
Table 2. Representative physiographic features
Landforms
(1) Fan remnant
Elevation
800–4,700 ft
Slope
2–15%
Climatic features
The climate of the Mojave Desert has extreme fluctuations of daily temperatures, strong seasonal winds, and clear skies. The climate is arid and is characterized with cool, moist winters and hot, dry summers. Most of the rainfall falls between November and April. Summer convection storms from July to September may contribute up to 25 percent of the annual precipitation. Average annual precipitation is 3 to 7 inches. Mean annual air temperature is 57 to 75 degrees F. The average growing season is about 180 to 360 days.
Table 3. Representative climatic features
Frost-free period (average)
360 days
Freeze-free period (average)
Precipitation total (average)
7 in
Bar
Line
Figure 1. Monthly average minimum and maximum temperature
Influencing water features
There are no influencing water features associated with this site.
Soil features
The soil associated with this site are very deep and derived from mixed sources. A continuous desert pavement of at least 80 percent gravels covers the soil surface. Surface rock fragments are coated with a shiny patina (desert varnish) on the exposed surfaces. The rock fragments tend to be imbedded, leaving a smooth soil surface. The soils are well drained to excessively drained, available water capacity is very low and runoff is very low to low. Soil series associated with this site include Gypwash, Heleweiser, Oldspan and Varwash. The soils typically are loamy-skeletal and have an ochric epipedon and a calcic horizon.
Table 4. Representative soil features
Surface texture
(1) Gravelly fine sandy loam
(2) Extremely gravelly fine sandy loam
(3) Extremely gravelly loam
Family particle size
(1) Loamy
Drainage class
Well drained to excessively drained
Permeability class
Moderate to moderately rapid
Soil depth
72–84 in
Surface fragment cover <=3"
50–95%
Surface fragment cover >3"
10%
Available water capacity (0-40in)
1.8–3.9 in
Calcium carbonate equivalent (0-40in)
10–60%
Electrical conductivity (0-40in)
4 mmhos/cm
Sodium adsorption ratio (0-40in)
5
Soil reaction (1:1 water) (0-40in)
7.9–9
Subsurface fragment volume <=3" (Depth not specified)
8–70%
Subsurface fragment volume >3" (Depth not specified)
15%
Ecological dynamics
This is a very stable plant community so long as the desert pavement is not disturbed. This is a very low producing site with very restricted plant diversity. Annual forbs account for most of the variability in production. Introduced annual forbs and grasses may invade this site.
Most fires in the Mojave Desert are infrequent and of low severity because production of annual and perennial herbs seldom provides a fuel load capable of sustaining fire. Fires in creosotebush scrub were an infrequent event in pre-settlement desert habitats, because fine fuels from winter annual plants were probably sparse, only occurring in large amounts during exceptionally wet winters. Fire kills many creosotebush. Creosotebush is poorly adapted to fire because of its limited sprouting ability. Creosotebush survives some fires that burn patchy or are of low severity. Range ratany is a drought tolerant perennial. It is generally considered to be a climax species in desert communities. It is a valuable browse plant, however under heavy grazing pressure it will decrease. The intricately branched round shape of range ratany provides valuable shelter for small mammals and birds. Range ratany generally reproduces sexually from seed, but has also been known to sprout post fire (Griffith 1991).
Desert pavement formed as a function of eolian erosion and deposition, therefore the site is not vulnerable to wind erosion if surface clasts are intact. If disturbed, the fine grained materials of the vesicular horizon will be released into the air potentially causing ecological and health problems (Yonovitz and Drohan 2009). Anthropogenic disturbances disrupt the pavement surface and increase erosion. However, studies have shown that soil functions related to pore morphology are not significantly affected by disturbance. Characteristics of the vesicular horizon, including the non-connected nature of the pores and its effect on restricting infiltration are able to rapidly recover to pre-disturbance conditions (Yonovits and Droham 2009). The implications of this are that the increased availability of nitrogen will not facilitate increase vegetative growth because infiltration will continue to be impeded even following disturbance.
Well-developed desert pavements can require thousands of years to form (Graham et al. 2008). Even at maturity, pavement surfaces are characterized by a dynamic stability. Stone mobility is an important aspect of pavement longevity. Disturbances can also be repaired by this process if not too extensive (Haff and Werner 1996). Natural mechanisms influencing stone mobility include animal movement and running water.
This state is representative of the natural range of variability under pristine conditions. Plant community phase changes are primarily driven by long-term drought. Insect attack and wildfire are infrequent, but have long-term impacts on the plant community. The plant communities of this site are dynamic in response to changes in disturbance regimes and weather patterns.
Community 1.1 Reference Plant Community
The reference plant community is dominated by creosotebush.
Potential native vegetative composition is about 5% perennial and annual forbs and 95% shrubs. Approximate ground cover (basal and crown) is less than 4 percent.
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
23
71
143
Grass/Grasslike
1
2
4
Forb
1
2
3
Total
25
75
150
State 2 Invaded
The Invaded State is characterized by the presence of non-native annuals in the understory. A biotic threshold has been crossed, with the introduction of non-native annuals that cannot be removed from the system. Ecological resiliency has been reduced by the presence of non-native annual species and a reduction in the cover of desert pavement. Non-native species have the potential to alter disturbance regimes significantly from their natural or historic range of variability.
Introduced annuals such as red brome, schismus and redstem stork's bill have invaded the reference plant community and have become a dominant component of the herbaceous cover. This invasion of non-natives is attributed to a combination of factors including: 1) surface disturbances, 2) changes in the kinds of animals and their grazing patterns, 3) drought, and 4) changes in fire history. These non-natives annuals are highly flammable and promote wildfires where fires historically have been infrequent.
Community 2.1 Plant Community Phase 2.1
This community is compositionally similar to the Reference Plant Community, with the presence of non-native annuals and reduced surface gravels. Following small scale disturbances desert pavements are able to heal due to the mobility of surface clasts. This plant community is identified as “at-risk”. If surface disturbance is not discontinued the site will be highly susceptible to erosion.
State 3 Eroded State
The Eroded State is characterized by persistent and severe surface disturbance, reduced vegetative cover and increased bare ground. A biotic threshold has been crossed, with the loss of long-lived native vegetation. This threshold causes changes in abiotic components of the site leading to active soil erosion.
Community 3.1 Plant Community Phase 3.1
This plant community is characterized by loss of perennial vegetative cover and reduced surface gravels. Non-natives are present in the plant community. Rain, wind, and surface water all contribute to increased erosion. Ecological processes including infiltration and nutrient cycling are severely reduced.
Transition 1 State 1 to 2
The introduction of non-native species due to anthropogenic disturbances including OHV use, dry land farming, grazing, linear corridors, mining, military operations and settlements.
Transition 2 State 2 to 3
Continued surface disturbances will disturb protective surface creating an eroded state.
Additional community tables
Table 6. Community 1.1 plant community composition
Livestock Interpretations:
This site has limited value for livestock grazing, due to the very low forage production. Creosotebush is unpalatable to livestock. Consumption of creosotebush may be fatal to sheep.
Stocking rates vary over time depending upon season of use, climate variations, site, and previous and current management goals. A safe starting stocking rate is an estimated stocking rate that is fine tuned by the client by adaptive management through the year and from year to year.
Wildlife Interpretations:
Creosotebush is unpalatable to most browsing wildlife.
Hydrological functions
Runoff is very low to low and permeability is moderate to moderately rapid.
Other products
Creosotebush has been highly valued for its medicinal properties by Native Americans. It has been used to treat at least 14 illnesses. Twigs and leaves may be boiled as tea, steamed, pounded into a powder, pressed into a poultice, or heated into an infusion.
Other information
Once established, creosotebush may improve sites for annuals that grow under its canopy by trapping fine soil, organic matter, and symbiont propagules. It may also increase water infiltration and storage.
Supporting information
Type locality
Location 1: Clark County, NV
Township/Range/Section
T27S R65E S25
UTM zone
N
UTM northing
3938071
UTM easting
710939
General legal description
Approximately 14 miles northeast of Searchlight and 2 miles southeast of Opal Mountain on the west side of the Colorado River, Clark County, Nevada. This site also occurs in southern Lincoln and southern Nye Counties.
Other references
Graham R.C., D.R. Hirmas, Y.A. Wood, and C. Amrhein. 2008. Large near-surface nitrate pool in soils capped by desert pavement in the Mojave Desert, California. Geology. 36.3: 259-262.
Marshall, K. A. 1995. Larrea tridentata. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2010, May 24].
McFadden, L.D., S.G. Wells, and M.J. Jerinovich. 1987. Influences of eolian and pedogenic processes on the origin and evolution of desert pavement. Geology. 15: 504-508.
Pavlik, B.M. 2008. The California Deserts: an ecological rediscovery. University of California Press.
Wood, Y.A., R.C. Graham, and S.G. Wells. 2005. Surface control of desert pavement pedologic process and landscape function, Cima volcanic field Mojave Desert, California. Catena. 59: 205-230.
Yonovitz, M. and P.J. Drohan. 2009. Pore morphology characterists of vesicular horizons in undisturbed and disturbed arid soils; implication for arid land management. Soil Use and Management. 25: 293-302.
Contributors
GKB
Approval
Sarah Quistberg, 2/24/2025
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)
P Novak-Echenique
Contact for lead author
State Rangeland Management Specialist
Date
05/12/2010
Approved by
Sarah Quistberg
Approval date
Composition (Indicators 10 and 12) based on
Annual Production
Indicators
Number and extent of rills:
Rills are none. Rock fragments armor the soil surface.
Presence of water flow patterns:
None
Number and height of erosional pedestals or terracettes:
None
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are
not bare ground):
Bare Ground <20%; surface rock fragments up to 95%; shrub canopy < 5%.
Number of gullies and erosion associated with gullies:
None
Extent of wind scoured, blowouts and/or depositional areas:
None
Amount of litter movement (describe size and distance expected to travel):
Fine litter (foliage from grasses and annual & perennial forbs) expected to move distance of slope length during intense summer convection storms or rapid snowmelt events. Persistent litter (large woody material) will remain in place except during large rainfall events.
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range
of values):
Soil stability values should be 1 to 4 on most soil textures found on this site. (To be field tested.)
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Surface structure is typically strong very thick to moderate medium platy. Soil surface colors are light and typified by an ochric epipedon. Organic matter of the surface 2 to 3 inches is less than 1 percent.
Effect of community phase composition (relative proportion of different functional groups) and spatial
distribution on infiltration and runoff:
Sparse shrub canopy and associated litter provide some protection from raindrop impact.
Presence and thickness of compaction layer (usually none; describe soil profile features which may be
mistaken for compaction on this site):
Compacted layers are none. Subsoil argillic horizons should not be interpreted as compacted.
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):
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or
decadence):
Dead branches within individual shrubs common and standing dead shrub canopy material may be as much as 30% of total woody canopy; mature bunchgrasses commonly (<20%) have dead centers.
Average percent litter cover (%) and depth ( in):
Between plant interspaces trace to 5%, depth < ¼ inch
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
For normal or average growing season ± 75 lbs/ac. Favorable years ± 150 lbs/ac and unfavorable years ± 25 lbs/ac
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:
Potential invaders on this site include red brome, redstem filaree, and Mediterranean grass.
Perennial plant reproductive capability:
All functional groups should reproduce in average and above average growing season years. Little growth or reproduction occurs during extended or extreme drought conditions.
The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
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