Epple Anne Orth - Plants of Arizona: a field guide

The author wishes to thank the following for their invaluable assistance in identifying the more difficult plant subjects:

Dick Anderson, Chiricahua National Monument

Arizona-Sonora Desert Museum Botany Department, Tucson

Michael Bencic, Wupatki National Monument

Dr. Susann Biddulph

Jane Cole, Desert Botanical Garden, Phoenix

Dr. Carol Crosswhite, Boyce Thompson Southwestern Arboretum

Robert Dyson, Alpine Ranger District

Karen Foster, Saguaro National Park West

Peggy Lu Gladhill, Alpine Ranger District

Wendy Hodgson, Desert Botanical Garden, Phoenix

Philip D. Jenkins, The University of Arizona, Tucson

Ron Kearns, Kofa Mountain Wildlife Refuge

Les Landrum, Arizona State University, Tempe

Dr. Charles Mason, The University of Arizona, Tucson

Sandy Mcmahan, Saguaro National Park West

Vince Ordonez, Apache-Sitgreaves National Forest

Barbara Phillips, Coconino National Forest

Dr. Donald J. Pinkava, Arizona State University, Tempe

Patrick Quirk, Desert Botanical Garden, Phoenix

Roy Simpson, Chiricahua National Monument

Kathy Warren, Grand Canyon National Park

The diversity of plant life in Arizona spans six main life zones, from a low point of 70 feet near Yuma to a high point of 12,670 feet in the San Francisco Peaks near Flagstaff. Although certain species characterize specific zones, others frequently overlap several zones. The contour of the landcanyons or mountain slopesalso influences the variety of flora within a zone. Rainfall, too, greatly affects life within a given environment. Thus, life zones are merely guides, rather than well-defined territories. Climbing 1,000 feet approximates traveling northward about 300 miles and results in a temperature drop of about five degrees.

The Lower Sonoran Zone is situated below 4,500 feet. Here, creosote, jojoba, paloverde, mesquite, ironwood, saltbush, bursage, and cacti abound. The plants in this zone endure high temperatures and low precipitation. Spring annuals survive as seeds, some for decades. When temperatures are just right and rainfall in the fall and winter (January and February) is sufficient, the seeds germinate. These so-called ephemerals (of very short duration) develop quickly, burst into blossom, then soon go to seed. In contrast, paloverde, mesquite, ironwood, and bursage survive desert conditions because of their reduced leaf area. Others, such as jojoba and creosote, have specialized leaves for desert survival, while the ocotillo and brittlebush shed their leaves entirely during drought conditions. Still others, such as the cacti and certain bushes, have vestigial leaves or have modified their leaves to spines over evolutionary time.

The Upper Sonoran Zone ranges from 4,500 to 6,500 feet. At these elevations rainfall is more plentiful. Here, grasslands and sagebrush, as well as woodlands of oak, juniper, and pinyon pine are found. Here, too, lie large areas of chaparral with thickets of manzanita.

Between 6,500 and 8,000 feet lies the Transition Zone. Abundant rainfall at these altitudes produces huge stands of ponderosa pines. Scattered among these pines grow junipers, Gambel oaks, and Douglas firs.

The Canadian Zone, at 8,000 to 9,500 feet, is the province of cool, moist, fir forests. Douglas fir dominates this zone, with a mixture of blue and Engelmann spruce, quaking aspen, and white or subalpine fir.

Within the Hudsonian Zone (9,500 to 11,500 feet) grow spruce, fir, and bristlecone pines. These trees are usually stunted due to a short growing season; often they are twisted from the windy conditions found at these higher elevations.

The Alpine Zone, at above 11,500 feet, is represented on the San Francisco Peaks by sedges, lichens, grasses, and alpine wildflowers. It is above the timberline.

Each of the above zones is rich in wildflowerssome species are unique to a certain zone; others are present in several zones.

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