Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland

Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland


View west, about ¼ mile east of Tub Spring, 9170 feet, Chiricahua Mts. North-facing slope is dominated by aspen, with 40-59% cover, typically 80 feet tall, and 15-24% cover of spruce, 75 feet tall. White fir is a typical understory species (1-4%), while Rocky Mt. maple and box elder add another 5-9% cover at heights up to 25 feet. June 14, 2010.


The aspen-spruce ecosystem is limited to the crest of the Chiricahua Mountains, reaching to the summit of Chiricahua Peak at nearly 9800 feet, and down to 8500 feet in shady north-facing draws. Cooler, north-facing slopes account for 64% of the 1755 acres of aspen/spruce ecosystem, a higher percentage than any other ecosystem in this study. In contrast, mesic slopes make up about 50% of the neighboring, downslope ecosystem, the Southern Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest and Woodland.

At these elevations, snow can persist through May. Clearings from windthrow or fire support bracken fern, NM raspberry (Rubus neomexicanus), rock spirea (Holodiscus dumosus), and Gambel’s oak. Otherwise, the forest floor holds few shrubs, and is instead strewn with spent aspen leaves, spruce needles, and downed trunks. Understory tree species are typically white fir, Douglas fir, Southwestern white pine, as well as juvenile spruce.

The underlying bedrock is volcanic and sub-volcanic (almost but not quite extrusive), middle Miocene to Oligocene (15 to 38 Mya).


View east along the north slope of Flys Peak, near Tub Spring, 9200 feet, June 2010, among spruce and aspen, with white fir and Douglas fir in the understory. Hiker is 56 inches tall. June 14, 2010.


View southwest along the Centella Point trail, with Flys Peak in back, right. Much of this ecosystem burned in the 1994 Rattlesnake Fire. Burned areas include Anita Park, Centella Point, Round Park, and the southwest side of Flys and Chiricahua Peaks. The post-fire tree regeneration includes aspen, as shown here in the foreground, and spruce, just beyond the hiker. June 15, 2010.
9300 ft., view WNW along trail between Centella Point and Long Park, 15 June 2010. Trees are mostly aspen and spruce, with occasional Douglas fir. Cover can exceed 80%.

The National Vegetation Classification System (NVCS) describes this ecosystem as extending from Northern Arizona to Montana, so the Chiricahuas must be considered an outlier. The description also states:

"Most occurrences at present represent a late-seral stage of aspen changing to a pure conifer occurrence. Nearly a hundred years of fire suppression and livestock grazing have converted much of the pure aspen occurrences to the present-day aspen-conifer forest and woodland ecological system."

This may or may not be the case in the Chiricahuas, where there are few areas of pure spruce. However, this may be due to this ecosystem occurring at its southernmost extent. 

Other vegetation classifications

The Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland ecosystem includes elements of several vegetation types mapped or described in other classification schemes. In each of the six classifications referred to below, the * symbol marks the vegetation type most similar to the Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland 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 Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland, as mapped in this effort.

Landfire Existing Vegetation Type (EVT)
Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland*
Southern Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest and Woodland
Madrean Lower Montane Pine-Oak Forest and Woodland

USFS Mid-scale Dominance Type
Upper Evergreen Forest Tree Mix (PIPO_PSME, PSME, TETX) *
Ponderosa Pine (PIPO)

USFS Plant Habitat Type (Potential Association)
Engelmann Spruce/Rocky Mt. Maple (PIEN/ACGL) *
Engelmann Spruce/Moss (PIEN/Moss)

USFS Potential Natural Vegetation Type (PNVT)
Mixed conifer with aspen*
Spruce-fir forest

Brown, Lowe, and Pase Biome
Rocky Mountain Subalpine Conifer Forest*

Southwest Regional ReGAP Ecological System
Rocky Mt. Aspen Forest and Woodland*
Madrean Upper Montane Conifer-Oak Forest and Woodland