Madrean Pinyon-Mt.Mahogany on Limestone

Madrean Pinyon-Mt.Mahogany on Limestone
The view south, at 6900 feet, near the summit of Mt. Glenn, Dragoon Mts., 31 August 2010. A mix of Pinyon pine (P. discolor; 2.5 meter tall, 10-14% cover) and mountain mahogany (Cercocarpus montanus, 1.3 m tall, 10-14%). On this east-facing slope the two species co-dominate, but on north facing slopes the pinyon dominates, while south slopes are mostly mountain mahogany. Agave palmeri, Dasylirion wheeleri, Yucca schottii, and Nolina microcarpa, combine for an additional 10-14% cover. Just upslope from this photo point (which has much exposed bedrock) are two abundant summer annuals, Mirabalis longiflora and a yellow comp with scruffy leaves, that are typically 0.5 – 0.8 m tall, and covered 26-40%. Here and there were oaks, with 1-4% cover, typically less than 3 m tall: Quercus chyrsolepis, Q. toumeyi, and Q. arizonica. Silktassel and Rhus choriophylla were common but not abundant. Uncommon, with less than 1% cover, were scattered squawbush (Rhus trilobata), locust (Robinia neomexicana), and an occasional patch of oreganillo (Aloysia wrightii). Grass is uncommon at this site, but can be locally common elsewhere in this ecosystem. Manzanita is notably absent.


The Madrean Pinyon-Mt. Mahogany Chaparral and Woodland on Limestone ecosystem occurs in the Dragoons and the northern and southern extremes of the Chiricahuas, from 4400 feet near Fort Bowie, to 7400 feet atop Mt. Glenn (Dragoons) and Shaw Peak (Chiricahuas). Within the study area, it is mapped only on Paleozoic limestone. Younger sedimentary rocks are common elsewhere, but are either (1) not extensive enough to map, or (2) did not significantly alter the flora. The ecosystem is generally on moderate to steep slopes, not on bajadas, with about 20% of mapped acres on slopes less than 18% (10 degrees), 77% on steep slopes of 18-70% (10-35 degrees), and 3% on very steep slopes exceeding 70%. These figures are similar to the pinyon-juniper-oak woodland ecosystem, which occurs in a similar elevation range.
Above, in this NE view of the Dragoons, the gray Paleozoic limestone (left and back) rises above the Cenozoic granites (right) of the West Stronghold.
Between 4400 feet and 5500 feet on southerly exposures the ecosystem is characterized by rosette grassland, with a 25-40% cover of sideoats, perennial three-awn, and tanglehead. Agave palmeri, Dasylirion wheeleri, and Yucca baccata are the most common big monocots (10-14% cover), with bear grass locally abundant. Also common are patches, up to an acre, of mariola (Parthenium incanum) and oreganillo (Aloysia wrightii), typically at 15-25% cover, and often in the company of the big yellow annual composite, Heliomeris longifolia.
On northerly exposures at these lower elevations, Rhus choriophylla and Quercus pungens often provide another 5-9% cover.
The lower elevations lack photo documentation (the camera, now deceased, was left on the roof of the car). Above 5500 feet, this ecosystem more strongly resembles the photos, below, taken during a walk up Mt. Glenn in the Dragoons.
The view southeast from Mt. Glenn, 7450 feet, with the distant slope showing the contact between the granite and limestone, 31 August 2010. The granite (back-right) supports dense oak- junipe-pinyon. The transition to limestone (back-center) is apparent from the switch to small shrubs, mountain mahogany, and scattered pinyon.
The view northwest from Mt. Glenn, Dragoon Mts., 7450 feet, 31 August 2010. The foreground shows the tops of large pinyon on a north-facing slope (see photo below). Beyond is the relatively barren north end of the Dragoons, with Dragoon Peak in the back, right. Most of this view is within the limestone ecosystem, with few trees on the south facing slopes. Rosette grasslands are apparent on the lower slopes.
The view west from a steep north-facing slope near the summit of the Dragoons, Mt. Glenn, 7400 feet, 31 August 2010. The most mesic north slopes are dominated by Pinus discolor, 12 m tall, with 40-60% cover. The understory is Choisya arizonica, about 1 m tall with 26-40% cover, and hoptree, Ptelea angustifolia, about 1.2 m tall and 1-4% cover. Uncommon but present were Fendlerella utahensis and Holodiscus dumosus. Ground cover is mainly needle duff and a species of Oxalis (sorrel). There was a single oak.

Other Vegetation Classifications

The National Vegetation Classification System ( does not list an ecosystem that describes the Madrean Pinyon-Mt. Mahogany Chaparral and Woodland on Limestone ecosystem. With further scrutiny it will likely be divided into at least two ecosystems, one characterized by the higher elevation pinyon and mountain mahogany, and another lower ecosystem, with rosette grasslands on southerly exposures, most similar to the NRCS Ecological Site description for “Limestone Hills 16-20" p.z.”
Until then, it’s clear that the observed 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 Madrean Pinyon-Mt. Mahogany Chaparral and Woodland on Limestone 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 PaseBiome”, 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 Madrean Pinyon-Mt. Mahogany Chaparral and Woodland on Limestone, as mapped in this effort.

Landfire Existing Vegetation Type (EVT)
Madrean Pinyon-Juniper Woodland *
Madrean Encinal
Mogollon Chaparral
Madrean Oriental Chaparral (most similar to the Rhus choriophylla/Cercocarpus montanus Shrubland Association)
Madrean Lower Montane Pine-Oak Forest and Woodland
Apacherian-Chihuahuan Semi-Desert Grassland and Steppe
Apacherian-Chihuahuan Mesquite Upland Scrub

USFS Mid-scale Dominance Type
Desert and Semi-desert Shrub Mix (ARPU5, FOSP2, OPUNT_PRVE, PRVE, SDMX, SEDX)
Upper Pine-Oak (PINUS_QUERC)

USFS Plant Habitat Type (Potential Association)
Border Pinyon/Mexican orange (PIDI3/CHDUA) * (Note: sites visited during this study lacked alligator juniper, which the USFS lists as a common species in this habitat type)
Border pinyon/bullgrass (PIDI3/MUEM)
Border pinyon/evergreen sumac (PIDI3/RHVIC)

USFS Potential Natural Vegetation Type (PNVT)
Interior Chaparral *
Madrean Encinal Woodland

Brown, Lowe, and Pase Biome
Interior Chaparral *

Southwest Regional GAP Ecological System
Madrean Encinal *
Mogollon Chaparral (Note: ReGAP did not map the Madrean Oriental Chaparral in the study area)
Madrean Pinyon-Juniper Woodland
Madrean Lower Montane Pine-Oak Forest and Woodland
Apacherian-Chihuahuan Semi-Desert Grassland and Steppe
Apacherian-Chihuahuan Mesquite Upland Scrub