Apacherian-Chihuahuan Mesquite Upland Scrub

Photo Point 737
A south-facing slope, about one mile east of Four Mile Canyon, dominated by mesquite (Prosopis velutina), typically 4 to 5 feet tall and 41-60% cover, with associated whitethorn acacia, prickly pear, and snakeweed (Gutierrezia sarothrae). Bunchgrasses, especially Bouteloua curtipendala and Hilaria belangeri are present, but with less than 10% cover at this site. 4800 feet, 26 September 2011.
Photo Point 738
A view of a north-facing slope from the same station as the photo point above (PP 737), showing the effect of aspect. The cooler slope is dominated by juniper, scrub oak (Q. turbinella), and occasional single-needle pinyon. 4800 feet, 26 September 2011.
On the west side of the Galiuros, looking northeast toward Rhodes Peak on 17 December 2010, at 4100 feet. Here, about ½ mile south of Cienega Wash, mesquite, acacia, and prickly pear dominate, with associated barrel cactus, turpentine bush (Ericameria laricifolia) and buckwheat (Eriogonum wrighttii). Grasses are hardly apparent in December at this site, only a half-mile from a water tank. Photo by Lon and Queta.
The Apacherian-Chihuahuan Mesquite Upland Scrub ecosystem ranges from the lower limit of the study area at 3700 feet near the mouth of Kielberg Canyon on the west slope, to just over 5000 feet in numerous places. Most of this ecosystem is situated along the west slope between Kielberg and Schoenholzer Canyons, and on the northeast boundary, from Rattlesnake to Four Mile Canyon - among the lowest elevations in the entire study site.
This ecosystem takes in those lands with less than 10% cover of oak and conifers, but hold at least 15% cover of small trees and shrubs, most typically mesquite, fairyduster (Calliandra eriophylla), catclaw and whitethorn acacia, and wait-a-minute (Mimosa aculeaticarpa = M. biuncifera).  Grasses were also a feature of the ecosystem, but with an inverse relationship to the abundance of trees and shrubs. For instance, slopes holding only 20% tree/shrub cover could hold 25-40% grass cover, mostly typically sideoats, curly mesquite, and cane beardgrass. Exotic love grass (Eragrostis lehmanii) was uncommon.
On the east side of the Galiuros, this ecosystem transitions upslope to juniper savanna or woodland of single-needle pinyon and scrub oak, while on the west side the transition is usually to an oak encinal.
The majority of this ecosystem – 76% - was on steep slopes in excess of 10 degrees (>19%), in sharp contrast to the Apacherian-Chihuahuan Semi-Desert Grassland and Steppe, of which only 11% was on steep slopes.
In the Chiricahuas, Dragoon, and Dos Cabezas, this ecosystem occupied flats, fan, and steeper slopes, the latter often with much ocotillo, beargrass and rosette monocots (Agave, Yucca, Dasylirion wheeleri). In contrast, in the Galiuros there was no similar 'rosette' grassland, but instead oak encinal and/or juniper chaparral with large patches of bunchgrasses (see descriptions of these ecosystems). These were not mapped as part of this 'mesquite upland shrub.'
Other Vegetation Classifications
The Mesquite Upland Scrub ecosystem includes elements of several vegetation types mapped or described in other classification schemes. In each of the seven schemes referred to below, the * symbol marks the vegetation type most similar to the Mesquite Upland Scrub ecosystem.
And what is meant by ‘most similar’? For the USFS Plant “Habitat Type” (Potential Association) and the Brown, Lowe, and PaseBiome”, the * symbol denotes the best fit based on the description of the Habitat Type or Biome. For the Landfire, ReGap, and USFS PNVT and mid-scale dominance classifications, which are presently mapped as 30 meter pixels, the * symbol denotes the classification that was most commonly attributed within the Mesquite Upland Scrub, as mapped in this effort. The actual percentage attributed is given in parenthesis (%).
For example, the grassland polygons created by this study were used as a 'cookie-cutter' on the Landfire Existing Vegetation Type (EVT) layer (see methods). Within this study’s Mesquite Upland Scrub, 49% of the EVT pixels were attributed as Mogollon Chaparral, while 23% were Mesquite Upland Scrub.
Landfire Existing Vegetation Type (EVT, version 1.0.5)
Mogollon Chaparral (this includes the 'Quercus turbinella alliance')* (49%)
Apacherian-Chihuahuan Mesquite Upland Scrub (23%)
(Note: the Galiuros are mostly in Landfire's zone 15, but also extend in zone 25. The contact happens to be largely in the mesquite upland scrub, causing an apparent change in vegetation that is actually just an artifact of two maps with apparently different criteria. Zone 15 calls it Mogollon chaparral, while zone 25 gets it right, as mesquite upland scrub.)
Landfire Biophysical Setting (BpS, version 1.0.0, older but judged by the author as locally more accurate)
Mogollon Chaparral* (56%)
Apacherian-Chihuahuan Semi-Desert Grassland and Steppe (19%)
(Note: Apacherian-Chihuahuan Mesquite Upland Scrub is not a BpS in the Landfire scheme, but instead a shrub-invaded state of Apacherian-Chihuahuan Semi-Desert Grassland and Steppe)
USFS Mid-scale Dominance Type
Desert and Semi-desert Shrub Mix (27%) (ARPU5, FOSP2, OPUNT_PRVE, PRVE, SDMX, SEDX)
Grass Mix (13%) (ERAGR, GAMX, GPMX)
USFS Plant Habitat Type (Potential Association)
Not identified
USFS Potential Natural Vegetation Type (PNVT, based on 24 Oct 2011 draft map)
Semi-desert Grassland * (57%) (Note: Apacherian-Chihuahuan Mesquite Upland Scrub is not a PNVT in the Landfire scheme, but instead a shrub-invaded state of Semi-Desert Grassland)
Interior Chaparral (22%)
Madrean Encinal Woodland (20%)
Brown, Lowe, and Pase Biome
Semi-desert Grassland*
Southwest Regional Gap Ecological System (The top three were equally common attributions in the Gap map)
Apacherian-Chihuahuan Mesquite Upland Scrub * (38%)
Mogollon Chaparral (22%)
Madrean Pinyon-Juniper (19%)
Apacherian-Chihuahuan Piedmont Semi-Desert Grassland and Steppe (15%)


3748 ha
Area in acres: 
9261 acres