The Sonoran Desert at Organ Pipe National Monument, Arizona, USA.
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The Sonoran Desert at Organ Pipe National Monument, Arizona, USA. |
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. |
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Pinacate Preserve, Northwest Sonora, Spring 1998.
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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. |
April 15th, 2008. The wildflower season on the desert is definately winding down. It's been some two months since the last measurable rainfall and temperatures have been approaching 35°C in many locations. Nonetheless wildflowers can still be found. In the lowest, hottest locations only the cacti and perennial shrubs are in bloom now. Above 900 m elevation areas adjacent to washes and riparian areas are still repleat with a lot of blooming annuals as well as the trees and shrubs. This past weekend at Mesquite Wash I found dozens of wildflower species still in bloom.
March 10th, 2008. Reports are in from virtually every corner of the Sonoran Desert. Areas below 900m elevation are at or beyond the peak flowering period. Some of the lowest elevations, i.e. far western and southwestern Arizona are past the peak: many of the early bloomers are now gone to seed, but there are many species still blooming especially in shady spots. Plus those plants that typically bloom later in the spring (mostly perennials) are just beginning to open. Areas above 900 meters are very lush now. Much has already begun blooming and the peak will arrive soon. Flowering shrubs, cacti and trees should keep touring wildflower seekers busy for another two months at least. Temperatures this coming week will surpass 25°C, greatly accelerating the pace of the season.
March 1st, 2008. Temperatures the past week have pushed above 25°C and it became breezy over the weekend. The result: The wildflower season is advancing quickly. Today I toured the Saddle Mountain area finding many, many wildflowers in bloom. But, also a lot of the annuals where beginning to whither. Areas that got more rain, mostly east and north of Phoenix-Tucson should continue to have great shows of wildflowers for several weeks more.
The Wildflower season as of Feb. 17, 2008 is now under way. Driving west from Phoenix, Arizona I found patches of yellow bladderpod blanketing the Palo Verde Hills Popppies were beginning to pop their golden petals. Purple phacelias. Out west in Arizona the flowers seemed to be smaller than in 2005 -- the most abundant rainfall this year fell north and east of Phoenix. There the elevations are a bit higher and so the season will come more slowly. There should be an abundance of wildflowers well into late April. Then the cacti and ironwoods will put on there shows in May. Glorious.
Over the past 48 hours (Jan 27-28, 2008) much of the Sonoran Desert recieved its third installment of significant rainfall for the winter season. The rainfalls have been evenly spaced temporally and temperatures have been cool thus limiting evaporation and priming seeds for germination. This most recent precipitation event was signficant (over 50 mm) in many locations particularly in upslope areas north and east of Tucson and Phoenix. By mid February the show should be under way and peak sometime in March depending on temperature and elevations. If you plan your desert trip earlier or later simply change the elevation of your focus. Elevations up to 1400 m should have excellent shows of wildflowers well into May. And then the montane and alpine flowers enter the fray by June. Nature lovers rejoice! So many fans are flocking to Arizona for the Superbowl this week -- little do most realize that a more fabulous show will follow by a few weeks and is mostly free!
The cool weather has decreased evaporation. Last month (Jan 13) Arizona Natural History Field Trips participants visited the Buckeye Hills in sw Maricopa County, Arizona. We found plenty of damp soil, some puddles still holding run-off, and dense carpets of green seedlings. Little had begun blooming yet, but the lupine, phacelia, plantago and bladderpod seedlings were hopefull and very green. One more good rain will seal a good show. Even without another rain shower, flower seakers should begin finding success by mid February.
Spring 2005 Was Our Most Recent Spectacular Year! |
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The Sonoran Desert Naturalist is a personal effort authored and converted to html by myself, Mike Plagens. The parent page, www.arizonensis.org, is open to naturalists who wish to share what they've learned about any natural subject pertaining to Arizona. Currently there is no funding; all the research and writing is done in my spare time and the web hosting is paid from my 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. You can view a couple of her paintings and her new illustrated children's book: Click Here.
If you are intested in joining or organizing field trips to experience the Sonoran Desert then consider joining: : Arizona Natural History Field Trips.
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Updated: 11 April 2008
mjplagens@arizonensis.org
Copyright Michael J. Plagens, 1999-2008
