Madrean Encinal

A steep west-facing slope of Madrean encinal above the pine-oak corridor of Rattlesnake Canyon at 5100 feet (1570 m), about one mile south of Powers Garden, on 16 May 2011. The encinal is largely oaks, mostly Q. emoryi averaging 16 feet (5 m) and a shorter, small-leaved species similar to Q. arizonica x Q. grisea. Together the oaks give 25-40% cover. Grasses, especially Muhlenbergia spp, give a similar cover, and beargrass, Nolina microcarpa, runs a close second at 15-25% cover.  See Photo Point 472 below for a closer view of this hillside.

The Madrean Encinal ecosystem is defined most simply as those places where Madrean evergreen oaks are the dominant or co-dominant tree. Most always the encinal is topographically between the semi-desert grassland and the Madrean pine-oak. However, so are the Madrean Juniper Savanna and the Madrean Pinyon-Juniper. In the field, the proportion of oaks relative to pinyon and juniper can change swiftly with aspect and slope, so the ecosystem map is progressively less reliable as you approach the indicated boundary between the encinal and its neighboring ecosystem.

 

Nevertheless, there are consistent patterns within the encinal, as mapped by this study.

 

1) Encinal was the most widespread ecosystem in this study, covering 41,400 acres. Madrean Pinyon-juniper was a close second, with 40,315 acres.

 

2) Encinal was more variable in species composition than either juniper savanna or pinyon-juniper woodland. Within the Redfield Canyon watershed in the southern part of the study area, Arizona oak, emory oak, and Mexican blue-oak were the typical species. Within the Rattlesnake Canyon watershed, in the central study area, Mexican blue-oak drops out, and a small-leaved, short-statured version of Arizona oak (similar to Q. grisea) becomes common on drier aspects. In the northern part of the study area, within the Four-Mile Canyon watershed, the encinal is notably sparse on the oaks, which typically give 15-20% cover, but mountain mahogany can be locally dominant.

 

3) Encinal is generally in steep country, with only 12% of the areas mapped as encinal on relatively gentle slopes of less than 10 degrees (19 percent). The figure is 25% for juniper savanna. Pinyon-juniper, however, is steeper yet, with only 2% on gentle slopes.

 

4) Quercus turbinella was not a major player in the encinal, although it does become common and even co-dominant in the far northern study area.

 

5) On cooler aspects of slopes built of looser colluvium (as opposed to bedrock), encinal can become dense and shrubby. Where manzanita is common, co-dominant, or dominant, and where combined cover of short-statured trees and shrubs (less than 5 m) exceeds 60%, it was mapped as Mogollon chaparral, not encinal. However, in areas where oaks formed small copses (< one hectare) of taller trees (> 5 meters) with over 60% cover, these were mapped as part of the encinal, because they had open understories. See examples below, Photo Points 783 and 78

 

6) Encinal apparently favors colluvium over bedrock, with the latter favored by pinyon-juniper woodland. This is clearest along the reach of Rattlesnake Canyon, above (south) Powers Garden, where the colluvium on the east side is generally encinal, and the rockier west side is pinyon-juniper. See image below.

 

 

7) Because it was hard to distinguish between manzanita and small oak – actually, often impossible – it was equally hard to say if some of the alluvial fans along the toe of the mountain were mostly oak and juniper, or mostly manzanita and juniper. Oak was the indicator species for the encinal, so it is likely that some areas that are in fact encinal were wrongly mapped in this study as savanna. The converse is also true.

 

This is an open patch on the steep west-facing slope shown in Photo Point 474 (above), about one mile south of Powers Garden, above Rattlesnake Canyon, on 16 May 2011, at 5100 feet (1570 m). The oaks, mostly Q. emoryi and a small leaved species, are small and desiccated in the foreground, but more typically average 16 feet (5 m), and give 25-40% cover. Grasses, especially Muhlenbergia spp, give a similar cover, and beargrass, Nolina microcarpa, runs a close second at 15-25% cover. Under the oak canopy is an understory of small Pinus discolor, at 1-4% cover. Rhamnus crocea, Agave palmeri, and Mimosa sp. were present but uncommon.

The view northwest to a slope above Willow Creek, one mile west of Four Mile Canyon, at 5300 feet (1600 m), 27 September 2011. Quercus arizonica is the dominant tree, 16 feet (5 m) tall, and with 15% to 25% cover. Juniperus deppeana and Nolina microcarpa each give another 1-4% cover, while Dasylirion wheeleri (sotol) adds another 5-9 % cover. Most common of all are bunchgrasses (mostly sideoats, Bouteloua curtipendala) with 25 - 40% cover. Manzanita is notably uncommon, with less than 1% cover.

  

The view NNW from Cake Mountain, 6500 feet (2000 m), on 27 Sept 2011. The summit ridge on the left is blackened from a recent fire, carried by grasses, Nolina microcarpa, Cercocarpus montanus,  and Quercus arizonica (ID'ed with binoculars).

The view NE towards the Santa Teresa Mts., from near the summit of Cake Mountain, 6000 feet (1830 m), 27 September 2011. This is the typical encinal of the northern part of the study area, dominated by Quercus arizonica, but with common associates Cercocarpus montanus (mountain mahogany) and Agave schottii on the rockier and/or sunnier exposures. The thick patch of oaks in the foreground is shown below in Photo Point 783.

 

Quercus arizonica, typically 23 feet tall (7 m) on a steep east facing slope on Cake Mountain, 5900 feet (1770 m), 27 September 2011. Canopy cover was 60-80%, with little else besides Muhlenbergia sp (5-9%) in the understory, with occasional Agave and Rhamnus crocea.

Another copse of oak, near Photo Point 783 (above), near Cake Mountain on 27 September 2011, 5900 feet (1770 m).  Oaks, mostly Q. arizonica but with some Q. hypoleucoides, dominate with 60-80% cover. On this relatively flat site, the tree average 26 feet (8 m) tall.

 

 27 September 2011. Alligator juniper and Arizona oak co-dominate, each with 15-25% cover, and 5-6 m tall. In the left foreground is Garrya wrightii, a common associate at 5-9 % cover, and 5 feet tall (1.5 m). Less common was silverleaf oak, with 1-4 cover. Grasses, mostly bullgrass (Muhlenbergia), gave another 15-255 cover. See also Photo Point 792 below.

 

 

A north-facing slope about a half- mile west of the confluence of Willow and Four Mile Canyons, at 5000 feet (1500 m). Quercus arizonica is the dominant tree, averaging 20 feet tall (6 m) and 10-14% cover. Common associates are single-needle pinyon (4 m, 1-4%), alligator juniper (4 m, 1-4%), mountain mahogany (2.2 m, 5-9%), and beargrass, Nolina microcarpa (1.2 m, 5-9%). Bunchgrasses add another 15-25% cover.

The view ESE along the West Divide Trail, about a quarter-mile south of Rhodes Peak, 6500 feet (2000 m), on 15 May 2011. Grasses and oaks (a small-leaved species, typically 8 feet tall (2.5 m), and similar to Q. grisea) each give 25-40% cover. Most of the oaks in the middle-ground appeared dead, but were apparently waiting for rain. Snakeweed and beargrass were common associates, each with 5-9 % cover. Present but uncommon were manzanita, alligator juniper, Quercus turbinella and Q. hypoleucoides. Despite abundant pinyon pine in the neighborhood (they darken the hillslope in the back right) there are no pinyon within a hundred meters of the camera station, and the entire west slope (to camera right) down to Forest boundary at 4100 feet was encinal. The ridge south of Rhodes Peak showed signs of a previous burn.

An example of what is not encinal, but nonetheless was mapped as encinal, because it is a small inclusion within the mapped encinal. The view is looking northwest to Sycamore Canyon, along the Tortilla Trail from Deer Creek to Powers Garden. This ridge was mostly spidergrass (Aristida ternipes) and other bunchgrasses, combining for 15-25% cover, and mountain mahogany (10-14% cover), with associated alligator juniper, beargrass, snakeweed (Gutierrezia sarothrae), and Agave. Oaks were locally absent.

 

 

The Madrean Encinal 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 Madrean Encinal ecological system.

 

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 Madrean Encinal, as mapped in this effort. The actual percentage attributed is given in parenthesis (%).

 

For example, the Madrean Encinal 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 encinal ecosystem, 42% of the EVT pixels were attributed as Madrean Pinyon-Juniper, 27% as Mogollon Chaparral, and 11% were attributed as Madrean Encinal.

 

Madrean Pinyon-Juniper * (42%)

Mogollon Chaparral (27%) (includes Quercus turbinella shrubland alliance)

Madrean Encinal (11%)

Madrean Juniper Savanna (4%)

Apacherian-Chihuahuan Mesquite Upland Scrub (4%)

Madrean Lower Montane Pine-Oak Forest and Woodland (3%)

 

Landfire Biophysical Setting (BpS, version 1.0.0, which is older but judged by the author as locally more accurate)

Madrean Pinyon-Juniper * (30%)

Mogollon Chaparral (40%)

Madrean Encinal (14%)

Madrean Juniper Savanna (4%)

Madrean Lower Montane Pine-Oak Forest and Woodland (4%)

 

OakJuniperPinyon Mix * (64%) (JUDE2, JUDE2_QUAR, JUDE2_QUEM, JUDE2_QUERC, JUMO, JUNIP_QUERC, PICEB, PIMO, QUAR, QUAR_QUEM, QUEM, QUEM_QUOB, QUERC, QUOB)

Desert and Semi-desert Shrub Mix (19%) (ARPU5, FOSP2, OPUNT_PRVE, PRVE, SDMX, SEDX)

Upper Pine-Oak (10%) (PINUS_QUERC)

Grass Mix (2%) (ERAGR, GAMX, GPMX)

Quercus emoryi/Boutleloua curtipendala QUEM/BOCU * (savanna)

Quercus arizonica/Muhlenbergia emersleyi QUAR/MUEM * (savanna)

Quercus emoryi/Dasylirion wheeleri QUEM/DAWH2 (savanna)

Quercus emoryi/Arctostaphylos pungers QUEM/ARPU5

Quercus arizonica/Rhus trilobata QUAR/RHTR

Quercus oblongifolia/Bouteloua (mixed) QUOB/mixed Bouteloua (southwest Galiuros)

Quercus oblongifolia/ Dasylirion wheeleri QUOB/DAWH2 (southwest Galiuros)

 

Encinal, as mapped in this study, may also include elements of:

Pinus discolor/Muhlenbergia emersleyi PIDI3/MUEM

 

Madrean Encinal * (42%)

Interior Chaparral (32%)

Madrean Pine-oak (18%)

Semi-desert grassland (6%)

Brown, Lowe, and Pase Biome

Madrean Evergreen Forest and Woodland (Encinal Series)

 

Southwest Regional GAP Ecological System

Madrean Pinyon –Juniper * (33%)

Mogollon Chaparral (32%)

Madrean Pine-oak (18%)

Madrean Encinal (3%)