Apacherian-Chihuahuan Semi-Desert Grassland and Steppe

The view west to Basset Peak, from a hill north of Ash Creek near the forest boundary, 4900 feet (1500 m), 2 October 2011. Bunchgrasses give 41-60% cover, with the most common species being Bouteloua curtipendala, B. gracilis, B. repens, Aristida ternipes, Bothriocloa barbanodis, and Lycurus setosus. Agave palmeri (or A. chrysantha) are ubiquitous, yet with only 1-4% cover; less obvious, but more common (10-14% cover), is Grindelia squarrosa (curlycup gumweed; synonym= Grindelia nuda var. aphanactis). At the toe of this slope the gumweed becomes the dominant. This site is similar to the Ecological Site Description (NRCS) for "Loamy Slopes 16-20" p.z."

 

Looking northeast from a ridge about ½ mile SE of Deer Creek Cabin, 5300 feet (1600 m), 13 May 2011. Before the summer storms, and after grazing, the grasses are short but still dominant, with 20-35% cover, mainly from Bothriocloa barbanodis and various gramas. Associates include Agave palmeri, sotol (Dasylirion wheeleri) and occasional juniper, oak and squawbush (Rhus trilobata) on cooler aspects. The drainage on the upper right was mapped as part of the Juniper Savanna.

In this view SSE towards the Winchester Mountains, 3 to 10 foot tall (1-3 m) Juniperus deppeana are common in this grassland on skeletal soils at the southeastern end of the Galiuros, between Bear Canyon and Ash Canyon. This photo shows the upper limit of 15-20% of trees and shrubs that were mapped as part of the grassland. 4900 feet (1500 m), Oct. 3, 2011.

 

The Apacherian-Chihuahuan Semi-Desert Grassland and Steppe ecosystem ranges from 4750 feet along the eastern boundary of the Coronado, to 6100 feet on the slopes of Saddle Mountain at the southern edge of the Galiuros.  The latter is an exception. The majority of the mapped lands are flattish alluvial fans that extend well past the forest boundary into Sulphur Springs and Aravaipa Valleys. Only 11% of the mapped grassland was on slopes exceeding 10 degrees (18%). Upslope, in steeper country, the grasslands typically grade into a juniper savanna.

 

The ecosystem is characterized by dominant and diverse perennial grasses, largely native. Perennial shrubs and trees typically have less than 15% total cover. Grassy areas with over 20% shrub and tree cover were mapped as either juniper savanna, Madrean encinal, or mesquite upland shrub. Areas with intermediate cover, 15-20% cover, could be mapped either way.

 

This ecosystem is not represented within the forest boundary on the west side, but likely existed there, in areas that are now mapped as part of the Apacherian-Chihuahuan mesquite upland scrub.

 

The Apacherian-Chihuahuan Semi-Desert Grassland and Steppe ecosystem includes elements of several vegetation types mapped or described in other classification schemes (although it is generally well-mapped by all methods). In each of the seven schemes referred to below, the * symbol marks the vegetation type most similar to the Apacherian-Chihuahuan Semi-Desert Grassland and Steppe ecosystem.

 

And what is meant by ‘most similar’? For the USFS Plant “Habitat Type” (Potential Association) and the Brown, Lowe, and Pase “Biome”, 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 Apacherian-Chihuahuan Semi-Desert Grassland and Steppe, 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 grasslands, 49% of the EVT pixels were attributed as Apacherian-Chihuahuan Semi-Desert Grassland and Steppe, while 24% were Mogollon Chaparral, and 15% were Apacherian-Chihuahuan Mesquite Upland Scrub.

 

Apacherian-Chihuahuan Semi-Desert Grassland and Steppe* (49%)

Mogollon Chaparral (24%)

Apacherian-Chihuahuan Mesquite Upland Scrub (15%)

 

Apacherian-Chihuahuan Semi-Desert Grassland and Steppe* (58%)

Mogollon Chaparral – a common misattribution (28%)

(Note: Apacherian-Chihuahuan Mesquite Upland Scrub is not a BpS in the Landfire scheme, but instead an uncharacteristic state of Apacherian-Chihuahuan Semi-Desert Grassland and Steppe)

 

Grass Mix *(79%) (ERAGR, GAMX, GPMX)

Desert and Semi-desert Shrub Mix (12%) (ARPU5, FOSP2, OPUNT_PRVE, PRVE, SDMX, SEDX)

 

 

Brown, Lowe, and Pase Biome

Semi-desert Grassland *

 

Southwest Regional GAP Ecological System
Apacherian-Chihuahuan Piedmont Semi-Desert Grassland and Steppe* (60%)
Apacherian-Chihuahuan Mesquite Upland Scrub (13%)
Chihuahuan Creosotebush, mixed desert and thorn scrub (8%)
Madrean Pinyon-Juniper Woodland (8%)