A wide variety of plant and animal life finds homes within Arizona's great range of elevations—more than 12,000 feet. Sensitive and endangered plant species receive protection from a state law that prohibits collecting or destroying most cacti and wildflowers without a permit from the landowner. Cacti need time to grow—a saguaro takes 50 years to mature—and cannot survive large-scale collecting. Some plants, such as the senita cactus and elephant tree, grow only in southern Arizona and Mexico.
Migratory birds often stop by the mountains and wetlands. The colorful parrot-like trogon bird and more than a dozen species of hummingbirds fly up from Mexico to spend their summers in the mountains of southeastern Arizona. Canada geese and other northern waterfowl settle in for the winter on rivers and lakes in the low desert.
To help simplify and understand the different environments of Arizona, some scientists use the Merriam system of life zones. Because plants rely on rainfall, which is determined largely by elevation, each life zone can be expected to occur within a certain range of elevations. The elevation ranges are not exact—south-facing mountain slopes receive more sun and lose more moisture to evaporation than north-facing slopes at the same level. Canyons and unusual rainfall patterns can also play havoc with classifications. Yet the life zones do provide a general idea of what kind of vegetation and animal life you can expect when traveling through the state.
Lower Sonoran Zone
Arizona's famed desert country of arid plains, barren mountains, and stately saguaro cacti covers about one-third of the state. The southern and western sections under 4,500 feet lie within this zone. The big cities and most of the state's population are here, too. With irrigation, farmers find the land good for growing vegetables, citrus, and cotton. Cacti thrive: you'll see the prickly pear, cholla, and barrel, as well as the giant saguaro—its white blossom is the state flower. Desert shrubs and small trees include the paloverde, ocotillo, creosote, mesquite, and ironwood. Flowering plants tend to bloom after either winter rains (the Sonoran or Mexican type) or summer showers (the Mojave or Californian type).
Most desert animals retreat to dens or burrows during the heat of the day, when ground temperatures can reach 150°F. Look for wildlife in early morning, evening, or at night: kangaroo rats, squirrels, mice, desert cottontail, black-tailed and antelope jackrabbits, spotted and striped skunks, gray and kit foxes, ringtail, javelina, bighorn sheep, coyote, and the extremely shy mountain lion. Common birds include the cactus wren (state bird of Arizona), Gambel's quail, Gila woodpecker, roadrunner, hawks, eagles, owls, and common raven. Sidewinder and western diamondback rattlesnakes are occasionally seen. The rare Gila monster, identified by a beadlike skin with black and yellow patterns, is the only poisonous lizard in the United States; it's slow and nonaggressive but has powerful jaws. Also watch out for poisonous invertebrates, especially the small slender scorpion—its sting is dangerous and can be fatal to children. Spiders and centipedes can also inflict painful bites. Careful campers check for unwanted guests in shoes and other items left outside.
Strange Creatures of the Desert
Upper Sonoran Zone
This zone encompasses 4,500- to 6,500-foot elevations in central Arizona and in widely scattered areas throughout the rest of the state. Enough rain falls here to support grasslands or stunted woodlands of juniper, pinyon pine, and oak. Chaparral-type vegetation grows here too, forming a nearly impenetrable thicket of manzanita and other bushes. Many of the animals found in the Lower Sonoran Zone live here as well. You might also see black bear, desert mule deer, white-tailed deer, and the antelope-like pronghorn. Rattlesnakes and other reptiles like this zone best.
The sweet-smelling ponderosa pines grow in this zone, at 6,500-8,000 feet, where much of the winter's precipitation comes as snow. Ponderosas cover many parts of the state, but their greatest expanse—the largest in the country—lies along the southern Colorado Plateau, from Williams in north-central Arizona eastward into New Mexico. Gambel oak, junipers, and Douglas fir commonly grow among the ponderosas.
Squirrels and chipmunks rely on the pinecones for food; other animal residents here include desert cottontail, black-tailed jackrabbit, spotted and striped skunks, red fox, coyote, mule deer, white-tailed deer, elk, black bear, and mountain lion. Wild turkey live in the woods, along with the Steller's jay, screech owl, hummingbirds, juncos, and common raven. Most of the snakes—gopher, hognosed, and garter—are harmless, but you might also run across a western diamondback rattler.
Only five percent of Arizona's old-growth forest remains. It survives in remote canyons and on a few mountains, some under federal protection. Scientists find the old-growth forests an amazingly complex interaction of life and decay. Hundreds of species of fungi, insects, birds, animals, and plants feed or protect one other in ways still being discovered. We've also learned about forest management from these old systems. Checks and balances in these forests limit damage of insect and mistletoe infestations, an advantage that managed forests of uniformly aged trees don't share. Fires in the old growths burn cool and close to the ground and do little harm, because the shade from mature trees prevents excessive growth of brush and thickets of small trees; also, the branches of mature trees lie above the reach of most fires. Natural fires move through every five to seven years, clearing the underbrush and fertilizing the soil with ash. Even in death, a large tree can stand 50 years, providing a home for generations of birds and insects. Foresters once removed these old snags as fire hazards, but now we know that many birds depend on them.
Douglas firs dominate the cool, wet forests between 8,000 and 9,500 feet, mixed with Engelmann and blue spruce, white and subalpine fir, and quaking aspen. Little sunlight penetrates the dense forests, where the trees function as their own windbreak. Grasses and wildflowers grow in lush meadows amid the forests. You'll find Canadian Zone forests on the Kaibab Plateau of the Grand Canyon's North Rim, the San Francisco Peaks, the White Mountains, and other high peaks. Look and listen for squirrels as they busily gather cones for the long winter. Deer and elk graze in this zone, but rarely higher.
Strong winds and a growing season of less than 120 days prevent trees from reaching their full size at elevations from 9,500 to 11,500 feet. Forests here receive twice as much snow as their neighbors in the Canadian Zone just below. Often gnarled and twisted, the dominant species are Engelmann and blue spruce, subalpine and corkbark fir, and bristlecone pine. This zone appears in Arizona only atop the highest mountains.
On a bright summer day, the trees, grasses, and tiny flowering alpine plants buzz with insects, rodents, and visiting birds. Come winter, most animals move to lower and more protected areas.
In Arizona, only the San Francisco Peaks exhibit this zone, which lies above about 11,500 feet, the upper limit of tree growth. Freezing temperatures and snow can blast the mountain slopes even in midsummer. About 80 species of plants, many also present in the North American Arctic, manage to survive on the Peaks despite the rocky soil, wind, and cold. One species of groundsel and a buttercup appear only here. Seasonal visitors include a dwarf shrew and three species of birds, the Lincoln and white-crowned sparrows and the water pipit.
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