San Francisco Peaks - Ecology

Ecology

The biologist Clinton Hart Merriam studied these mountains and surrounding areas in 1889, describing a set of six life zones found from the bottom of the Grand Canyon to the summit of the mountains, based on the factors of elevation, latitude, and average precipitation. He designated their characteristic flora, as follows:

• Lower Sonoran Zone - Sonoran Desert plants
• Upper Sonoran Zone - Pinyon and Juniper woodlands
• Transition Zone - Ponderosa Pine forests
• Canadian Zone - Mixed Conifer Forest
• Hudsonian Zone - Spruce-Fir or Subalpine Conifer Forest
• Arctic-Alpine Zone - alpine tundra

Merriam considered that these life zones could be extended to cover all the world's vegetation types with the addition of only one more zone, the tropical zone.

The San Francisco Peaks themselves contain four of the six life zones. The four life zones which are found along the slopes of the San Francisco Peaks are listed below along with their approximate elevation ranges, dominant tree species found within each of the four life zones and average annual precipitation of each life zone:

• Ponderosa Pine forests — The elevation of ths zone ranges from approximately 6,000 to 8,500 feet (1,800 to 2,600 m) above sea-level. The dominant tree species is the Southwestern Ponderosa Pine (Pinus brachyptera Engelm.). Gambel oak (Quercus gambelii) is a common associate of the ponderosa pine at lower elevations in the forest along with New Mexico locust (Robina neomexicana). At higher elevations, associates include southwestern white pine (Pinus strobiformis), Rocky Mountain Douglas-fir, (Pseudotsuga menziesii var. glauca), Rocky Mountain white fir (Abies concolor var. concolor), and Quaking Aspen (Populus tremuloides). The average annual amount of precipitation in this zone is 18 to 26 inches (460 to 660 mm).

• Mixed conifer forest — The elevation of this zone ranges from approximately 8,000 to 9,500 feet (2,400 to 2,900 m) above sea-level. Species such as Douglas-fir (Pseudotsuga menziesii var. glauca), White Fir (Abies concolor), Limber Pine (Pinus flexilis var. reflexa), Blue Spruce (Picea pungens), and less commonly Southwestern White Pine (Pinus flexilis) form mixed stands in this community, with Ponderosa Pine (Pinus brachyptera Engelm.) joining the mix on warmer slopes. The average annual amount of precipitation in the mixed conifer forest is 25 to 30 inches (630 to 760 mm).

• Subalpine conifer forest — The elevation of this zone varies from approximately 9,500 to 11,500 feet (2,900 to 3,500 m) feet above sea-level. The dominant tree species of this zone are Englemann Spruce (Picea engelmannii subsp. engelmannii), Corkbark Fir (Abies lasiocarpa var. arizonica), Quaking Aspen (Populus tremuloides) and the Rocky Mountain Bristlecone Pine (Pinus aristata). The average annual amount of precipitation in the subalpine forest is 30 to 40 inches (760 to 1,000 mm).

• Alpine tundra — The San Francisco Peaks are the home of the only alpine tundra environment in Arizona, occupying 1,200 acres (4.9 km2) above 10,600 feet (3,200 m). Only a few small herbaceous plants have established themselves in the tundra. One of these species, is the endemic and threatened San Francisco Peaks groundsel (Packera franciscana), which is found nowhere else in the world. The average annual amount of precipitation in the tundra is 35 to 40 inches (890 to 1,000 mm).