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The Sonoran Desert of Baja California

by Danielle Chaikin

      The Sonoran Desert covers over 100,000 square miles, stretching from southern Arizona about 250 miles south of the border into Mexico. Because the Baja California peninsula was once attached to western Mexico, the Sonoran Desert is found on both sides of the Sea of Cortez and most of Baja California is part of this desert.

     The Sonoran Desert in Baja California is divided into four sub-regions, each with its own distinct geography and flora. The San Felipe Desert, in the northeast part of the peninsula, is the driest with an average of 5 cm of rainfall per year. The Gulf Coast Desert is a narrow strip that runs along the Sea of Cortez from Bahia Los Angeles, all the way to the tip of the peninsula. This area receives moisture from tropical storms and nearby mountains create arroyos and underground streams. On the Pacific Side, the Vizcaino Desert is the largest sub-region, stretching from El Rosario, 1000 km to the south. Precipitation in this area is low, but plants receive moisture from the condensation of heavy coastal fog. South of the Vizcaino is the Magdalena Plains (sometimes the combined area is referred to as the Central Desert). Coastal mangroves, swamps, and large underground aquifers that support agriculture differentiate this region.

Climate
     Temperatures vary along the Baja California peninsula, but as a rule, temperatures are higher as you travel south, the Pacific coast is cooler than the Gulf coast, and the lower the elevation, the higher the temperature. The desert is virtually absent of frost and summer temperatures often reach above 100° F. Baja California has very low precipitation typical of deserts. Mean annual precipitation on the entire peninsula is 15.3 cm., but there are great variances of rainfall throughout the peninsula, and from year to year. There are two main seasons of precipitation in Baja California. Winter storms bring gentle rains from the Pacific, but because of mountain ranges on the peninsula, these storms usually fail to reach the deserts on the Gulf Coast. The wettest storms on the peninsula come during the late summer or early fall, as chubascos. These tropical hurricanes form over warm water, close to the equator. Facing little resistance, the air masses gain speed and circling winds can top 200 kph. Feeding on the warm waters of the tropical Pacific and Gulf, these storms bring large amounts of moisture. When chubascos reach ground, they often wreak havoc, but many areas of the peninsula depend on these violent storms as their main source of rain.

Plants
     The mountains of the peninsula can receive substantial rains and periodically, large amounts of water are washed down the river beds. Even though the arroyos may appear dry most of the year, moisture is retained in the soil and they are lined with shrubs, trees and flowering plants. Because of the twice-yearly rainfall, both winter and summer annuals grow on the peninsula and perennial plants are able to survive as well. Desert soils are very low in organic matter, and because of the high rate of evaporation, they tend to have high concentrations of salts. In flatter regions of the desert, the tightly packed soils become saturated easily and most of the water runs off of them during the heavy rains. Creosote bush and bur sage dominate the driest areas of the desert. Gentle sloping areas, known as bajadas, are more conducive to plant diversity. These areas accumulate the mountain erosion, with the resulting soil a mixture of rocks, gravels, sands and silts. The varying particle sizes create soil with an open structure that allows water to penetrate the surface.

      The high air, surface and soil temperatures and low humidity of deserts limits plant in animal life to species that are adapted to the harsh terrain. Desert plants tend to have small leaves and many drop their leaves in drought conditions. Some desert plants have dense coverings of hairs that protect their photosynthetic surfaces from intense sunlight and reduce water loss from evaporation. Other plant adaptations include thick leaves, which have less leaf surface area per unit of photosynthesizing tissue, fewer stomata, and structures on stomata that prevent evaporation. Many succulent plants reduce water loss by conducting photosynthesis at night when temperatures are low.

     Mesquite and paloverde are two trees commonly found on the peninsula. These trees can survive in the poor soil due to nitrogen-fixing bacteria in their roots that provide them with nutrition. Mesquite is common along arroyos and in low-lying deserts. Like many desert plants, mesquite has an extensive shallow root system to capture water quickly, but it also has deep tap roots to capture water from far below the surface. Paloverde trees lose their leaves in a drought, but have green stems that allow them to continue to photosynthesize. Other common plants and trees include ocotillos, agaves, yuccas, acacia trees, Fan palms and Mexican blue palms.

     The desert of the peninsula is home to many unusual plants. Many trees have swollen trunks for storing water. Elephant trees have smooth, light-colored bark and swollen elephantine trunks and branches. Their small leaves drop during dry periods, resulting in naked trees with odd silhouettes. Another odd-looking tree is the boojum (cirio), which exists only in Baja California and in one isolated colony on mainland Mexico, directly across the Gulf from the rest of the boojums. There are more than 110 species of cacti on the peninsula, including the world's largest cactus, the cardon. Cacti have several adaptations to survive the sun and scarce rainfall. Spines on cacti help break up the suns rays, and thick, waterproof skins prevent water loss. Cacti have extensive root systems that extend horizontally within the top three inches of the soil and are able to capture moisture over a large area. Many cacti have a barrel shape, which provides a large volume of water storage with a small surface area. Columnar cacti, such as the cardon and saguaro, have vertical framework that allows their trunks to expand to store large amounts of water when it is available, then contract when water is scarce.

Animals
     Animals of the peninsula also display adaptations for the hot, arid conditions of the desert. Most desert creatures are light gray or buff colored, an adaptation that provides camouflage and prevents light absorption. Most animals adapt to the heat by modifying their behavior – some limit their activities to cooler hours and locations, while others burrow to avoid the heat of the sun. Members of the dog family and birds use panting as a means of cooling. Some rodents use estivation (the summer version of hibernation) to survive the hottest parts of the year, while others use short periods of dormancy that last only a few hours. Many rodents live in the desert, including squirrels, gophers, mice, rats and rabbits. The kangaroo rat has special adaptations so it never needs to drink water, obtaining moisture through the seeds it eats, living in burrows with higher humidity, condensing moisture in its nasal passages, and excreting uric acid in a concentrated paste, instead of in liquid form. Bats are plentiful in the Sonoran Desert and play a very important role as the chief pollinators for flowering cacti and agaves. Amphibians and reptiles, such as lizards, geckos, chuckwallas and spiny tailed iguanas, are all common in the desert.

     Mule deer inhabit Baja California and there is even an endemic peninsular variety. Mule deer live in the lower foothills and canyons and have exceptionally large ears which alert them to danger. Adults are prey to mountain lions, while fawns are prey to coyotes. Large herds of Desert Bighorn sheep once roamed Baja California, and while their numbers have been reduced by big game hunting and overgrazing there are still several thousand on the peninsula. These sheep are well adapted to the dry conditions, only needing to drink every three to five days. The peninsular pronghorn is an endangered species which lives in the Vizcaino Desert where they draw moisture from the Pacific fog. There are only about 200 left in existence and they are protected by the Mexican government.

     The most widespread mammal on the peninsula is the coyote. In many areas, the coyote is the top predator in the food chain. Coyotes are omnivorous, they hunt small animals, eat carrion, and eat plant matter such as cactus fruits. They are mainly active at night or during the early morning. Other carnivores commonly found on the peninsula include the kit fox, gray fox, ringtail, bobcat, lynx, and badger. Mountain lions on the peninsula do not live in the desert itself, but in the adjacent mountainous regions. Where mountain lions exist, they become the top predator and play an important role in culling old, weak and sick deer. Mountain lions are mostly nocturnal and capture their prey by ambush, relying on their speed and leaping ability.

     The Baja California peninsula hosts around 300 species of birds, most of which are coastal or pelagic birds. Common coastal birds include the Magnificent Frigate and the Brown Pelican. Birds of prey and carrion eaters thrive in the desert, with numerous falcons, hawks, American Kestrels, Turkey Vultures and owls in the region. Other common desert birds include Cactus Wrens, woodpeckers, hummingbirds, and roadrunners. Many desert birds are carnivores, with a substantial amount of their moisture intake coming from the juices of the animals and insects they feed on.

     Because deserts cover a large part of the earth's surface, they have always had a great deal of human contact. As we continue to develop desert areas, we need to pay close attention to this unique ecosystem. While deserts can appear barren and devoid of life, there is a wide variety of animal and plant life that has adapted to this harsh environment, utilizing the limited resources in an extremely efficient manner. By protecting and studying the desert, humans may learn to better utilize our own dwindling resources.

If you enjoyed this, check out the rest of our Los Cabos Information pages:

  • The Tropical Dry Forest of the Sierra de la Laguna
  • Cardon cactus (pachycereus pringlei)
  • San Jose Estuary
  • Golf in Los Cabos
  • Los Cabos Shopping Guide


    Sources:

    Alcock, John. 1985. Sonoran Desert Spring. Chicago. University of Chicago Press.

    Cummings, Joe. 2000. Baja: Tijuana to Cabo San Lucas, 4th ed. Emeryville. Avalon Travel Publishing, Inc.

    Deacon, Dr. Jim. and Dr. Sharon von Broembsen. Desert Ecology. http://helios.bto.ed.ac.uk/bto/desertecology/index.htm#home

    Friesen, Larry Jon. 2001. Biology 122 Ecology. http://www.saturdaze.net/eco/

    Kirk, Ruth. 1973. Desert: The American Southwest. Boston. Houghton Mifflin Company.

    Molles, Manuel C. 2002. Ecology, concepts and applications, 2nd ed. New York: McGraw-Hill.

    Reveal, James L. 1999. Biomes of North America Lecture Notes. Norton-Brown Herbarium, University of Maryland. http://www.inform.umd.edu/PBIO/biome/lec35f3.html

    Roberts, Norman C. 1989. Baja California Plant Field Guide. La Jolla, CA. Natural History Publishing Company.

    Zwinger, Ann. 1983. A Desert Country Near the Sea. New York. Harper & Row, Publishers.

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