Apacherian-Chihuahuan Upland Scrub

ID:

Description:

The view north, at 4500 feet, Happy Camp Canyon, 13 September 2010, Dos Cabezas Mts. The dominant species is prickly pear, averaging 1.0 meter tall, with 15-39% cover, with Lehmans love grass running a close second, 0.7 meters tall, with 15-25% cover. The dark green shrubs are mesquite and catclaw, typically 1.5 meters tall and adding 10-14% cover combined. Common associates include Agave palmeri (1.0 meter,1-4% cover), Gutierrezia sarothrae (1-4%), and ocotillo (5-9%). Other common (1-4% cover) bunch grasses include sideoats and sprucetop grama.

Description

The Apacherian-Chihuahuan Mesquite Upland Scrub ecosystem ranges from the lower limit of the study area at 3900 feet in the foothills of the Dragoons to 6900 feet near Pothole Peak in the southeastern Chiricahua Mountains. It is a catch-all ecosystem, meaning that it takes in the lands that do not fit in other ecosystems, including many that have little or no mesquite (despite the name of the ecosystem, which comes from the NVCS). The unifying feature is a lack of trees (more than 3 meters), at least 10-15% shrub cover, and grass coverage generally less than 15%. In this scheme, ocotillo, beargrass and rosette monocots (Agave, Yucca, Dasylirion wheeleri) are shrubs.

This ecosystem is most similar to the Apacherian-Chihuahuan Semi-Desert Grassland, which is defined by less than 10-15% shrubs, “diverse perennial grasses” (NVCS), and elevations under 5500 feet. In practice, it was possible to distinguish between the semi-desert grassland and the upland scrub on alluvial fans and broad canyon bottoms, where the larger mesquite and catclaw were obvious on the imagery. But on the slopes it was more difficult to guess the identity of the shrubs. For instance, a common feature of these landscapes is the fairyduster (Calliandra eriophylla), a pretty little plant that pretty much vanishes when the grasses respond to the summer rains.

Without more time in the field, the solution was to simply map as “mesquite upland scrub’ all those areas lacking trees but holding a lot of unknown shrubs. Such places were found mostly on the SE side of the Chiricahuas, near Horseshoe Canyon; along Mesa Draw above Leslie Canyon National Wildlife Refuge; and skirting the Dragoons and Dos Cabezas on all sides, typically at elevations under 6000 feet. On slopes and fans below limestone mountains, this ecosystem is generally absent, with creosotebush and/or whitethorn the dominant species.

Much of the ecosystem in on relatively gentle terrain: 72% occupies slopes less than 10 degrees (18% slope), and 28% is on slopes greater than 10 degrees. In comparison, 20% of the pinyon-juniper-oak ecosystem is on slopes less than 10 degrees. Only 1% of the Madrean Upper Montane Conifer-Oak is on similar terrain.

The view north in Happy Camp Canyon, Dos Cabezas Mts., 4500 feet, 13 September 2010. The far slopes are dominated by prickly pear, while the valley bottom is primarily catclaw (Acacia greggii), 1.2 meters tall, with 25-39% cover. Common associates include mesquite, snakeweed, Fairyduster, and Lehman’s love grass. Both the slopes and the valley bottom are within the mesquite upland scrub ecosystem

The view NE on a slope above Horseshoe Canyon, Chiricahua Mts., 4800 feet, 12 June 2010. Grasses including Eragrostis and Setaria appear to dominate with 15-25% cover, but at this site a pair of annuals that includes a mustard (Lepidium) give a cover of 41-60%. Common associates include coral bean, desert broom, Agave palmeri, prickly pear and ocotillo.

The view NW from Happy Camp Canyon Road, about 1 mile SE of the Indian Bread Rocks, Dos Cabezas Mts., 4000 feet, 12 September 2010. Burroweed (Isocoma tenuisecta ), mesquite, and the annual needle grama grass were the most common species, with each giving 10-14% cover. Catclaw and wolfberry were common associates.

The view SE from the road to Council Rocks, west side of the Dragoons, 31 August 2010, 4900 feet. Lehman’s love grass with a 15-25% cover of mesquite.

Other Vegetation Classifications

The Apacherian-Chihuahuan Mesquite Upland Scrub ecosystem includes elements of several vegetation types mapped or described in other classification schemes. In each of the six schemes referred to below, the * symbol marks the vegetation type most similar to the Apacherian-Chihuahuan Mesquite Upland Scrub ecosystem.

And what is meant by ‘most similar’? For the USFS Plant “Habitat Type” (Potential Association), the USFS “Potential Natural Vegetation Type” (PNVT), and the Brown, Lowe, and Pase “Biome”, the * symbol denotes the best fit based on the description of the Habitat Type, PNVT, or Biome. For the Landfire, ReGap, and USFS mid-scale classifications, which are presently mapped at a 30 meter resolution and were used in creating the map, the * symbol denotes the classification that was most commonly attributed within the Apacherian-Chihuahuan Mesquite Upland Scrub, as mapped in this effort.

NOTE: In previous remote sensing efforts (ReGAP, Landfire), the computer algorithm attempts to identify the nature and origin of the shrubs – e.g., Sonoran Palo Verde or Chihuahuan Mixed Salt Desert – but often gets it wrong. For instance, there are no palo verde or salt desert shrubs in the study area, so they won’t be cited in the lists below. One effect of this misattribution is to diminish the number of 30-meter pixels attributed to the mesquite upland scrub in the reGAP and Landfire studies; hence, mesquite upland scrub is not the most commonly attributed ecosystem in the rankings below.

Landfire Existing Vegetation Type (EVT)
Apacherian-Chihuahuan Semi-Desert Grassland and Steppe*
Apacherian-Chihuahuan Mesquite Upland Scrub
Madrean Encinal
Madrean Pinyon-Juniper Woodland
Mogollon Chaparral (dense shrubs)
Madrean Oriental Chaparral (dense shrubs)

USFS Mid-scale Dominance Type
Desert and Semi-desert Shrub Mix * (ARPU5, FOSP2, OPUNT_PRVE, PRVE, SDMX, SEDX)
Grass Mix (ERAGR, GAMX, GPMX)
OakJP (JUDE2, JUDE2_QUAR, JUDE2_QUEM, JUDE2_QUERC, JUMO, JUNIP_QUERC, PICEB, PIMO, QUAR, QUAR_QUEM, QUEM, QUEM_QUOB, QUERC, QUOB)

USFS Plant Habitat Type (Potential Association)
Not determined

USFS Potential Natural Vegetation Type (PNVT)
Semi-desert Grassland *
(Note: the Provisional “Desert Communities – Upper” may, pending further research, describe much of this ecosystem. “Desert Communities – Lower”, does not, as the study area lacks species of lower desert communities.)

Brown, Lowe, and Pase Biome
Semi-desert Grassland *

Southwest Regional GAP Ecological System
Apacherian-Chihuahuan Semi-Desert Grassland and Steppe*
Apacherian-Chihuahuan Mesquite Upland Scrub
Madrean Encinal
Madrean Pinyon-Juniper Woodland
Mogollon Chaparral (dense shrubs)
Madrean Oriental Chaparral (dense shrubs)