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Upper Sonoran Desert Scrub

EVT 7091Sonoran Mid-Elevation Desert Scrub

CES302.035GNRShrubShrubland

Summary

This transitional desert scrub system occurs along the northern edge of the Sonoran Desert in an elevational band along the lower slopes of the Mogollon Rim/Central Highlands region between 750 and 1300 m. Stands occur in the Bradshaw, Hualapai, and Superstition mountains, among other desert ranges, and are found above Sonoran Paloverde-Mixed Cacti Desert Scrub (CES302.761) and below Mogollon Chaparral (CES302.741). Sites range from a narrow strip on steep slopes to very broad areas such as the Verde Valley. Climate is too dry for chaparral species to be abundant, and freezing temperatures during winter are too frequent and prolonged for many of the frost-sensitive species that are characteristic of Sonoran Paloverde-Mixed Cacti Desert Scrub (CES302.761), such as Carnegiea gigantea, Parkinsonia microphylla, Prosopis spp., Olneya tesota, Ferocactus sp., and Cylindropuntia bigelovii. Substrates are generally rocky soils derived from parent materials such as limestone, granitic rocks or rhyolite. The vegetation is typically composed of an open shrub layer of Larrea tridentata, Ericameria linearifolia, or Eriogonum fasciculatum with taller shrub such as Canotia holacantha (limestone or granite) or Simmondsia chinensis (rhyolite). The herbaceous layer is generally sparse.

Source: NatureServe Explorer

Vegetation

The vegetation is typically composed of an open shrub layer of Larrea tridentata, Ambrosia deltoidea, Ericameria linearifolia, or Eriogonum fasciculatum with taller shrubs such as Canotia holacantha (limestone or granite) or Simmondsia chinensis (rhyolite). Eastern Sonoran stands may have Acacia neovernicosa or Parthenium incanum preset that are more typical of Chihuahuan desert scrub. The herbaceous layer is generally sparse. The floristic description is based on several references including Brown (1982), Reid et al. (1999), and Sawyer et al. (2009).

Source: NatureServe Explorer

Environment

This desert scrub system occurs along the northern edge of the Sonoran Desert and forms an elevational band along the lower slopes of the Mogollon Rim/Central Highlands region between 750 and 1300 m. This system ranges from a narrow strip on steep slopes to very broad areas such as the Verde Valley. Stands also occur in the Bradshaw, Hualapai, and Superstition mountains, among other desert ranges. It is uncommon in the Mojave Desert. This system occurs above Sonoran Paloverde-Mixed Cacti Desert Scrub (CES302.761) and below Mogollon Chaparral (CES302.741) where climate is too dry for chaparral species to be abundant, and freezing temperatures during winter are too frequent and prolonged for many of the frost-sensitive species that are characteristic of Sonoran Paloverde-Mixed Cacti Desert Scrub (CES302.761). Substrates are generally rocky soils derived from parent materials such as limestone, granitic rocks or rhyolite. The environmental description is based on several references, including Brown (1982), Reid et al. (1999), NatureServe Explorer (2011), and Sawyer et al. (2009).

Source: NatureServe Explorer

Dynamics

Climate is the main driving ecological variable characterizing this system. Sites are too dry for chaparral species to be abundant, and freezing temperatures during winter are too frequent and prolonged for many of the frost-sensitive species that are characteristic of Sonoran Paloverde-Mixed Cacti Desert Scrub (CES302.761), such as Carnegiea gigantea, Parkinsonia microphylla, Prosopis spp., Olneya tesota, Ferocactus sp., and Cylindropuntia bigelovii. Fire appears to be infrequent by the presence of the fire-sensitive dominant shrub Larrea tridentata, which is very long-lived with clones living >10,000 years (Keeler-Wolf 2007) and very tolerant of drought and high temperatures with small, evergreen, resinous (highly flammable) leaves reducing evapotranspiration (Hamerlynck et al. 2002). It may die-back during extreme drought, but can sprout from the base (Meinzer et al. 1990). It has low recruitment and is slow to re-establish from seed (Keeler-Wolf 2007).

Simmondsia chinensis is important forage for wildlife species such as mule deer, jackrabbits, desert bighorn sheep (Gentry 1958, Miller and Gaud 1989), and may provide the best browse available within its range (Matthews 1994).

Source: NatureServe Explorer

Threats

Simmondsia chinensis is important forage for livestock such as cattle, goats and sheep (Matthews 1994). Cattle may browse Simmondsia chinensis severely enough to prevent any fruit development (Gentry 1958), and often consume it faster than it grows (Brooks 1978). However, in a study in southern Arizona, it appears tolerant of heavy browsing, but moderate browsing was recommended to maintain greater shrub size and forage production (Roundy and Dobrenz 1989).

Human development has impacted many locations throughout the ecoregion. High- and low-density urban and industrial developments also have large impacts. For example, residential development has significantly impacted locations within commuting distance to urban areas. Impacts may be direct as vegetation is removed for building sites or more indirectly through natural fire regime alteration, and/or the introduction of invasive species. Mining operations can drastically impact natural vegetation. Road building and power transmission lines continue to fragment vegetation and provide vectors for invasive species.

Source: NatureServe Explorer

Distribution

This system occurs along the northern edge of the Sonoran Desert in an elevational band along the lower slopes of the Mogollon Rim/Central Highlands region between 750 and 1300 m.

Source: NatureServe Explorer

Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Tree canopy

Carnegiea gigantea, Olneya tesota

Shrub/sapling (tall & short)

Canotia holacantha, Ericameria linearifolia, Hyptis emoryi, Larrea tridentata, Lycium andersonii, Parkinsonia microphylla, Simmondsia chinensis

Short shrub/sapling

Ambrosia dumosa, Encelia farinosa, Eriogonum fasciculatum, Opuntia bigelovii

Source: NatureServe Ecological System assessment

Ecologically Associated Animals (6)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Birds (2)

Common Name	Scientific Name	G-Rank
Greater Roadrunner	Geococcyx californianus	G5
Gila Woodpecker	Melanerpes uropygialis	G5

Reptiles (4)

Common Name	Scientific Name	G-Rank
Western Diamond-backed Rattlesnake	Crotalus atrox	G5
Panamint Rattlesnake	Crotalus stephensi	G4G5
Eastern Kingsnake	Lampropeltis getula	G5
Desert Spiny Lizard	Sceloporus magister	G5

Source: NatureServe Ecological System assessment

At-Risk Species Associated with this Ecosystem (1)

Species with conservation concern that are ecologically associated with this ecosystem type. G-Rank indicates global conservation status: G1 (critically imperiled) through G5 (secure). ESA status indicates U.S. Endangered Species Act listing.

Common Name	Scientific Name	G-Rank	ESA Status
Teddy-bear Cactus	Opuntia bigelovii	G3?	--

Source: NatureServe Ecological System assessment

Component Associations (1)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

Name	G-Rank
Ambrosia deltoidea / Simmondsia chinensis Shrubland	G4	NatureServe

State Conservation Ranks (1)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

State	S-Rank
AZ	SNR

Roadless Areas (14)

Inventoried Roadless Areas where this ecosystem is present, identified from LANDFIRE 2024 Existing Vegetation Type spatial analysis. Coverage indicates the proportion of each area occupied by this ecosystem type.

Arizona (14)

Area	Forest	Coverage	Hectares
Cimarron Hills	Coconino National Forest	11.1%	237.69
Lime Creek	Tonto National Forest	5.9%	1,010.16
Hackberry	Coconino National Forest	4.0%	289.71
Muldoon	Prescott National Forest	3.9%	92.25
Catalina St. Pk. Roadless Area	Coronado National Forest	3.5%	13.5
Horse Mesa	Tonto National Forest	2.6%	95.13
Sunset	Apache-Sitgreaves National Forests	2.1%	249.39
Boulder	Tonto National Forest	1.4%	235.62
Black Cross	Tonto National Forest	1.3%	30.78
Grief Hill	Prescott National Forest	1.2%	58.86
Picacho	Tonto National Forest	1.2%	23.13
Black Canyon	Prescott National Forest	1.0%	45.18
Butterfly Roadless Area	Coronado National Forest	1.0%	168.57
Sheridan Mountain	Prescott National Forest	0.5%	72.99

Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.