FREE ESSAY ON HOT AND DRY DESERT

HOT AND DRY DESERT

Hot and Dry Desert
The four major North American deserts of this type are the Chihuahuan, Sonoran, Mojave
and Great Basin. Others outside the U.S. include the Southern Asian realm, Neotropical
(South and Central America), Ethiopian (Africa) and Australian.
The seasons are generally warm throughout the year and very hot in the summer. The
winters usually bring little rainfall. Temperatures exhibit daily extremes because the
atmosphere contains little humidity to block the Sun's rays. Desert surfaces receive a
little more than twice the solar radiation received by humid regions and lose almost
twice as much heat at night. Many mean annual temperatures range from 20-25? C. The
extreme maximum ranges from 43.5-49? C. Minimum temperatures sometimes drop to -18? C.
Rainfall is usually very low and/or concentrated in short bursts between long rainless
periods. Evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling
and evaporates before reaching the ground. Rainfall is lowest on the Atacama Desert of
Chile, where it averages less than 1.5 cm. Some years are even rainless. Inland Sahara
also receives less than 1.5 cm a year. Rainfall in American deserts is higher-almost 28
cm a year.
Soils are course-textured, shallow, rocky or gravely with good drainage and have no
subsurface water. They are coarse because there is less chemical weathering. The finer
dust and sand particles are blown elsewhere, leaving heavier pieces behind.
Canopy in most deserts is very rare. Plants are mainly ground-hugging shrubs and short
woody trees. Leaves are "replete" (fully supported with nutrients) with water-conserving
characteristics. They tend to be small, thick and covered with a thick cuticle (outer
layer). In the cacti, the leaves are much-reduced (to spines) and photosynthetic activity
is restricted to the stems. Some plants open their stomata (microscopic openings in the
epidermis of leaves that allow for gas exchange) only at night when evaporation rates are
lowest. These plants include: yuccas, ocotillo, turpentine bush, prickly pears, false
mesquite, sotol, ephedras, agaves and brittlebush.
The animals include small nocturnal (active at night) carnivores. The dominant animals
are burrowers and kangaroo rats. There are also insects, arachnids, reptiles and birds.
The animals stay inactive in protected hideaways during the hot day and come out to
forage at dusk, dawn or at night, when the desert is cooler.
Semiarid Desert
The major deserts of this type include the sagebrush of Utah, Montana and Great Basin.
They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia,
Europe and northern Asia).
The summers are moderately long and dry, and like hot deserts, the winters normally bring
low concentrations of rainfall. Summer temperatures usually average between 21-27? C. It
normally does not go above 38? C and evening temperatures are cool, at around 10? C. Cool
nights help both plants and animals by reducing moisture loss from transpiration,
sweating and breathing. Furthermore, condensation of dew caused by night cooling may
equal or exceed the rainfall received by some deserts. As in the hot desert, rainfall is
often very low and/or concentrated. The average rainfall ranges from 2-4 cm annually.
The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand.
It has a fairly low salt concentration, compared to deserts which receive a lot of rain
(acquiring higher salt concentrations as a result). In areas such as mountain slopes, the
soil is shallow, rocky or gravely with good drainage. In the upper bajada (lower slopes)
they are coarse-textured, rocky, well-drained and partly "laid by rock bench." In the
lower bajada (bottom land) the soil is sandy and fine-textured, often with "caliche
hardpan." In each case there is no subsurface water.
The spiny nature of many plants in semiarid deserts provides protection in a hazardous
environment. The large numbers of spines shade the surface enough to significantly reduce
transpiration. The same may be true of the hairs on the woolly desert plants. Many plants
have silvery or glossy leaves, allowing them to reflect more radiant energy. These plants
often have an unfavorable odor or taste. Semiarid plants include: Creosote bush, bur sage
(Franseria dumosa or F. deltoidea), white thorn, cat claw, mesquite, brittle bushes
(Encelia farinosa), lyciums, and jujube.
During the day, insects move around twigs to stay on the shady side; jack rabbits follow
the moving shadow of a cactus or shrub. Naturally, many animals find protection in
underground burrows where they are insulated from both heat and aridity. These animals
include mammals such as the kangaroo rats, rabbits, and skunks; insects like grasshoppers
and ants; reptiles are represented by lizards and snakes; and birds such as burrowing
owls and the California thrasher.
Coastal Desert
These deserts occur in moderately cool to warm areas such as the Nearctic and Neotropical
realm. A good example is the Atacama of Chile.
The cool winters of coastal deserts are followed by moderately long, warm summers. The
average summer temperature ranges from 13-24? C; winter temperatures are 5? C or below.
The maximum annual temperature is about 35? C and the minimum is about -4? C. In Chile,
the temperature ranges from -2 to 5? C in July and 21-25? C in January.
The average rainfall measures 8-13 cm in many areas. The maximum annual precipitation
over a long period of years has been 37 cm with a minimum of 5 cm.
The soil is fine-textured with a moderate salt content. It is fairly porous with good
drainage. Some plants have extensive root systems close to the surface where they can
take advantage of any rain showers. All of the plants with thick and fleshy leaves or
stems can take in large quantities of water when it is available and store it for future
use. In some plants, the surfaces are corrugated with longitudinal ridges and grooves.
When water is available, the stem swells so that the grooves are shallow and the ridges
far apart. As the water is used, the stem shrinks so that the grooves are deep and ridges
close together. The plants living in this type of desert include the salt bush, buckwheat
bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus.
Some animals have specialized adaptations for dealing with the desert heat and lack of
water. Some toads seal themselves in burrows with gelatinous secretions and remain
inactive for eight or nine months until a heavy rain occurs. Amphibians that pass through
larval stages have accelerated life cycles, which improves their chances of reaching
maturity before the waters evaporate. Some insects lay eggs that remain dormant until the
environmental conditions are suitable for hatching. The fairy shrimps also lay dormant
eggs. Other animals include: insects, mammals (coyote and badger), amphibians (toads),
birds (great horned owl, golden eagle and the bald eagle), and reptiles (lizards and
snakes).
Cold Desert
These deserts are characterized by cold winters with snowfall and high overall rainfall
throughout the winter and occasionally over the summer. They occur in the Antarctic,
Greenland and the Nearctic realm. They have short, moist, and moderately warm summers
with fairly long, cold winters. The mean winter temperature is between -2 to 4? C and the
mean summer temperature is between 21-26? C.
The winters receive quite a bit of snow. The mean annual precipitation ranges from 15-26
cm. Annual precipitation has reached a maximum of 46 cm and a minimum of 9 cm. The
heaviest rainfall of the spring is usually in April or May. In some areas, rainfall can
be heavy in autumn. The soil is heavy, silty, and salty. It contains alluvial fans where
soil is relatively porous and drainage is good so that most of the salt has been leached
out.
The plants are widely scattered. In areas of shad-scale, about 10 percent of the ground
is covered, but in some areas of sagebush it approaches 85 percent. Plant heights vary
between 15 cm and 122 cm. The main plants are deciduous, most having spiny leaves. Widely
distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice,
grasshopper mice, and antelope ground squirrels. In areas like Utah, population density
of these animals can range from 14-41 individuals per hectare. All except the jack
rabbits are burrowers. The burrowing habit also applies to carnivores like the badger,
kit fox, and coyote. Several lizards do some burrowing and moving of soil. Deer are found
only in the winter.