Images © by the Norton-Brown Herbarium, University of Maryland,
unless otherwise credited.
BSCI 124 Lecture Notes
Department of Plant Biology, University of Maryland
LECTURE 35 - TERRESTRIAL BIOMES, Part 6 - Deserts
C. Warm Deserts: Sonoran Desert
Coastal mountains in southwestern California (and the Pacific Ocean in Baja
California) east to the Chihuahuan Desert of New Mexico (in the north) and
the Sierra Madre Occidental of Mexico (in the south). A portion is often
defined as the
Ocean fog on Cerro Tecolote, Baja California, Mexico
1. Mountains mostly low (except Sierra Juarez and San Pedro Mártir
in Baja California).
2. Precipitation biseasonal: falls during Dec through Mar and Jul through
Sep; mostly as rain, rarely as snow.
3. Winter temperature average above freezing; summer temperatures above
100° F common.
4. More than 200 days growing season.
Desert scrub near Rosarito, Baja California
1. Dominant shrub is creosote bush. Other common shrubs are crucifixion-thorn
(Canotia holacantha), jojoba (Simmondsia chinensis - although
originally discovered in California, the German botanist who named the plant
thought it came from China), white bur-sage (Ambrosia dumosa), brittlebush
(Encelia farinosa) and
Fouquieria splendens; F. diguetii - palo adán).
Fan palm near Santa Catavina, Baja California
2. Low trees include palo verde (Parkinsonia microphylla - yellow
palo verde; P. florida - blue palo verde; P. aculeata - Mexican
palo verde), species of catclaw (e.g., Acacia greggii - long-flower
catclaw), mesquite (e.g.,
glandulosa var. torreyana - Torrey's honey mesquite;
pubescens - American screw-bean), smoke tree (Dalea spinosa),
tesota (Olneya tesota), all members of the pea family
Fabaceae), elephant tree (Bursera microphylla,
image) and several
filifera; W. robusta
armarta; E. brandegeei).
3. Arborescent cacti: saguaro
gigantea), Organ Pipe cactus (Lemaireocereus thurberi), senita
(Lophocereus schottii), desert night-blooming cereus (Peniocereus
greggii), Emory's cereus (Bergerocactus emoryi) and cardón
Boojum near Parador Punta Prieta, Baja California
4. Most bizarre plant is the boojum tree (Fouquieria columnaris),
a columnar trunk with leaves and a few branches at the very top some 50-65
ft (15-20 m) above the ground.
But oh, beamish nephew, beware of the day,
If your Snark be a Boojum! For then
You will softly and suddenly vanish away,
And never be met with again!
Lewis Carroll, The Hunting of the Snark,
5. Rich diversity of annuals and perennial herbs, especially succulent ones;
numerous endemic species.
1. Mammals: Deer, mountain lion, bobcat, mountain sheep, fox, coyote, and
historically antelope. Feral goats and pigs are locally common and often
destructive. Smaller mammals include the jackrabbit, badger and the ring-tail
cat, a relative to the raccoon. Marine mammals include several species of
sea lion and seals.
2. Birds: Numerous shore and water fowl, hawks, resident song birds, large
numerous species of hummingbirds.
Saguaro on creosote bush on a recent lava flow, Arizona
1. Desert established over last 30,000 years but in present position only
about 4000 years.
2. Pack rat
middens are a good source of
record of desert
vegetation over last 20,000 years.
3. More grasses in the past than present.
1. Overgrazing is significant problem causing loss of many species.
2. Over collection of cacti, especially rare species, for commercial
3. Water availability remains a significant
4. ORV activities.
Saguaro and ocotillo at sunset near Tucson, Arizona
Desert main page
Main Terrestrial Biomes page
Last revised: 17 Oct 1997 - Reveal