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A mountainside poulated by Organ Pipes, Saguaros, Bursage and Palo Verde, photo © by Mike Plagens
The Sonoran Desert at Organ Pipe National Monument, Arizona, USA.

Sonoran Desert Naturalist

The Sonoran Desert of Southern Arizona and Northwestern Mexico is well known for its beauty and grandly spectacular cacti. The abundant cacti and other succulents defy the harsh climate with exuberant biodiversity. Few realize just how diverse and fascinating are the many other kinds of flora and fauna that also call this area home. The purpose of the The Sonoran Desert Naturalist, is to bring that experience to the Internet visitor, and to encourage all to come and make some discoveries. With an appreciation and love for all that the Sonoran Desert has to offer, hopefully we can safeguard it for our children and their children.

Observing nature in the desert might involve an extended journey into the remote desert wilderness, but many fascinating observations can also be made quite close to metropolitan Phoenix or Tucson. These pages are updated frequently with tales about plants, birds, insects and many other creatures I encounter while backpacking, hiking or going about my daily activities. Check out the Desert Wildflower Reports and Nature News featuring current natural events in the Sonoran Desert. In addition to our desert wilderness, The Sonoran Desert Naturalist provides loads of natural history information that can be seen in urban back yards and the city environment. In short, visitors to these pages experience the sights, sounds, smells (in words!), and textures of the Sonoran Desert. Come back often to see what's new!

What is a Desert?

For many people the concept of a desert means hot temperatures together with a profound shortage of water. There are, however, deserts that are cold for much if not all of the year. The Great Basin Desert in the United States and the Gobi Desert in Asia for example have bitterly cold winter seasons yet present the sparse vegetation and dry soils typical of deserts.

In Central Florida, where rainfall exceeds 1500 mm/year, there are sand hills that become very dry only days after rain because the water leaches out of the root zones very quickly. There are spiny cacti, drought tolerant shrubs together with birds and reptiles typical of "real" deserts. In the canopies of tropical American rain forests the tree branches themselves support epiphytic plants ("air plants") including cacti and bromeliads that very much resemble desert plants. Tree canopies are sunny and hot while gravity ensures that despite abundant rainfall, water is nearly always in short supply.

Within the boundaries of well recognized deserts there are wet places such as oases and river banks. Most authorities recognize a desert as a place that receives less than 300 mm of rain each year and where the evaporation rate exceeds the precipitation rate for the greater part of the year.

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What and Where is the Sonoran Desert?

The idea of a desert for many people conjures an image of shifting sand dunes or barren rocks devoid of vegetation and obvious animal life or habitation. Such areas do exist within the Sonoran Desert but for the most part this is a lush desert that receives 120 to 300 mm of precipitation each year. This is also a hot desert with daytime temperatures reaching or exceeding 40 C for much of the summer season, May to September, while hard freezes are uncommon during the mild winters. A very unique feature of the Sonoran Desert is that the rain arrives during two wet seasons, one generally December through March, the other July through Sept. The lack of hard freezes and moisture distributed through the year has promoted the abundance of succulents that can store water for later use.

The area generally recognized as the Sonoran Desert includes the southwestern third of Arizona, a small area of southeastern California, most of Baja California del Norte and the western half of Sonora, Mexico.

Sonoran Desert regions in Arizona and Mexico

Photo of Mike Plagens at Pinacate

Pinacate Preserve, Northwest Sonora, Spring 1998.

Sonoran Desert regions in Arizona and Mexico

Climate and vegetation types within the Sonoran Desert vary considerably across the region and with elevation in the many mountain ranges. In general, the amount and predictability of winter rainfall is higher in the west and lowest in the southeast. Summer wet season is more generous and lengthy in the southeast and shortest to the west. As one proceeds south within the Sonoran Desert the winter season is less severe, where more subtropical and tropical elements appear.

Upland Sonoran Desert (orange on map) occurs in southwestern Arizona and is characterized by a balanced distribution of winter vs. summer rainfall. Winter frosts are common, but not severe. Succulent cacti, highly drought tolerant shrubs, and thorny shrubs are equally common. Towards the north, especially on mountain slopes, the vegetation merges towards chaparral type vegetation which is characterized by dense thickets of evergreen shrubs that are also fire adapted. Then towards the northwest the Sonoran merges with the Mohave Desert where summer rainfall is usually scarce.

The driest and hottest region is the Colorado Desert (yellow on map) located in the lower Colorado River valley. Annual rainfall can be less than 50 mm while summer temperatures commonly approach 50 C. Areas of sand dunes occur in this area, and the Gran Desierto, located in Mexico to the east of the Colorado River presents the most inhospitable (yet also beautiful) terrain. Vegetation consists mostly of highly drought tolerant shrubs with few succulent cacti.

The Sonoran Desert in Sonora, Mexico has a longer, wetter summer rainy season with a drier winter (brown on map). Drought deciduous trees and shrubs become increasingly common towards the south, many of which are quite thorny. Succulent cacti are abundant and diverse. The Sonoran Desert rather gradually merges into the more southerly Tropical Dry Thorn Forest of Southern Sonora and Sinaloa.

The Sonoran Desert on Baja California is often referred to as the Vizcaino Desert (red on map). Cool moist weather comes in winter, the summers are not quite as hot due to the cooling effect of the Pacific Ocean, and occasionally summer brings good amounts of rainfall. Moisture from fog and dew can be considerable in some locations allowing epiphytes (air plants) to grow suspended from typical desert plants such as the ocotillo. Succulents including cacti, agaves and yuccas are abundant and extraordinarily diverse. The characteristic Boojum Tree plays as a succulent and a drought deciduous tree at the same time.

When I was a young boy, apparently at a very impressionable age, my mother read me a book (she read me a lot of books): Horton Hears a Who by Dr. Seuss. In a similar way to the story I've discovered that every tree, every shrub, and even the soil in the Sonoran Desert all have hidden worlds within and upon them. Worlds that only become apparent after close and quiet inspection. Now, even as I hurry along a highway past a palo verde or cactus by the side of the road, my imagination runs wild thinking about all the little creatures living mysterious lives hidden from view and neglected by everyone (almost). There are minute caterpillars munching leaves, even smaller worms tunneling within a single leaf, beetles smaller than pinheads tunneling beneath the bark of dead branches, bee pollinators provisioning nests for their babies deep within circuitous galleries. Bees, flies and butterflies providing pollination services for the open flowers and hidden deep underground the nymphal stages of cicadas, now silent and now devoted only to drawing juice from roots. Throughout the more than 1500 pages of the Sonoran Desert Naturalist I hope that you will learn that it is no fantasy at all - there really is an absolutely incredible world of intrigue and curiousness - smaller than a speck. Where there's solitude far out in the desert, away from cars and grinding business just stroll up to one of the straggling shrubs and immerse yourself and come to know some of the desert's small and not insignificant residents.

There's so much more to experience and learn!
Visit every page of the Sonoran Desert Naturalist:

  1. Back Yard Naturalist, Phoenix, Arizona -- Here I describe the many goings on that often go unnoticed in any urban landscape. Focus is especially on the plants and the insects that live on them, but also birds and reptiles. There are fascinating stories about aphids, bees, ants, cicadas, whiteflies, katydids, and butterflies. Find advice on how to make your yard wildlife friendly.
  2. Flora and Fauna News, Sonoran Desert Edition -- This page is designed to give a newspaper-like account of natural events that take place in the desert as well as in the Phoenix and Tucson urban habitats. By browsing through past issues the seasonal progression can be experienced.
  3. Desert Places -- This index page has numerous links to maps and descriptions of accessible trails, parks, canyons, mountains, and wild places that offer desert experiences. The natural history of Phoenix Mountains Preserves are described in detail. If you are intested in joining or organizing field trips to experience the Sonoran Desert then consider joining Arizona Natural History Field Trips.
  4. Field Guide -- This page has links to all the flora and fauna pictures as well as many, many species descriptions including Butterflies, Spiders, Beetles, Bugs and Grasshoppers.
  5. Common Birds: Desert, Riparian & Wetland and City
  6. Plant Families -- Sonoran Desert Flora arranged by family classification.
  7. Links -- An extensive and ever expanding list of web sites that offer information on exploring nature in the Sonoran Desert.
  8. Urban Habitats, Metropolitan Phoenix, Arizona -- Grenada Park, canals across the city, gardens and ponds, and a bat colony are examples of easily accessable nature experiences for city dwellers. The nature lover can make valuable observations of dragonflies and other aquatic insects. There are the usual urban birds inhabiting the parks as well as feral and released water fowl.

The Sonoran Desert Naturalist is a resource for sharing and learning about the Sonoran Desert. If you have photgraphs or information that you would like to contribute, please send them along by e-mail. Full credit will be given for all material used. Currently there is no funding; all the research and writing is done in our spare time and the web hosting is paid from private resources. If you have ideas, suggestions, comments or even donations please send an email (mjplagens@arizonensis.org). If you enjoy the watercolor paintings and photographs you should know that I thank my mother, Frances Plagens for inspiration.

If you are intested in joining or organizing field trips to experience the Sonoran Desert then consider joining our Facebook Group: Central Arizona Natural History Clubs.

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Follow These Links to More Sonoran Desert Pages:

News and current events in the Sonoran Desert Where to study and enjoy desert natural history Nature close to home.  Nature Gardening in Phoenix. Watercolors, photographs and line drawings of desert plants and animals. Nature around metropolitan Phoenix, Arizona Link library to other useful websites about deserts

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Updated: 18 July 2013
mjplagens@arizonensis.org

Copyright Michael J. Plagens, 1999-2013

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