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Wringing Life Out of Every Drop of Rain

The Mojave Desert is an environment of extreme heat, poor soil nutrients, limited soil water-holding capacity, and—worst of all—little water. Even when rains come to the Mojave, often a great amount of water falls in a very short time onto ground so dry that the rain runs off quickly, washing away skimpy desert soil in the process. Sometimes, high temperatures cause rain to evaporate before it reaches the ground. Wind frequently compounds these challenges by rapidly evaporating scarce moisture and covering plants with dust. Luckily, the Mojave’s plant and animal species have developed ingenious physiological and behavioral adaptations that allow them to thrive in such a harsh world. Here are some examples of the complex ways in which Mojave species have adapted.


Plants

Xerophytes are plants that have developed special means of storing and conserving 

Photo of cactus.

Many cacti and succulents take decades to reach maturity, and even then attain only a modest size.

DORAN SANCHEZ, BLM

water. To reduce transpiration, direct cooling air flow, shade themselves, and/or reflect hot sunlight, they often have few leaves, or have spines, thorns, or hairs instead; in some cases they use only their green “skin” to perform photosynthesis. Some xerophytes have leaves that are tough and waxy or coated with shiny oils, which also cuts down on transpiration, or they have small, fluttery leaves that help to cool the plants. Some species have spongy, shallow roots to take advantage of even the smallest amounts of rain, plant tissues that can store large amounts of water for later use, or ribs that direct moisture to the plant’s roots. The Joshua tree (Yucca brevifolia), various types of cacti, and Mojave sage (Salvia mojavensis) are all examples of Mojave xerophytes.

Phreatophytes are plants that grow extremely long roots, called tap roots, that allow them to obtain water from deep in the ground. Mesquites (Prosopis sp.) have the longest tap root of any desert species; it may reach down 25 m. The creosote bush (Larrea tridentata) is one of the most successful of all desert species because it uses a combination of several adaptations, including a deep tap root, a shallow root system, and wax-coated leaves that close their pores during the day to avoid loss of water. The creosote bush has the added advantage of being both bitter-smelling and -tasting; most animals won’t eat it, and other plants often won’t even grow near it, reducing competition for water.

Photo of creosote bushes.
Close up of creosote bush leaves.

Though the creosote bush may react to severe drought by dropping mature leaves or even whole branches, it always retains some younger leaves, which continue photosynthesis even under the most severe heat and drought conditions. After sufficient rainfall, miniature yellow flowers are followed by an abundant crop of dense, woolly seed balls, the fruit of the plant.

U.S. GEOLOGICAL SURVEY (TOP)
BLM RED ROCK CANYON NATIONAL CONSERVATION AREA (BOTTOM)

Desert perennials survive by remaining dormant during dry periods of the year, then “coming back to life” when water becomes available. For example, the ocotillo (Fouquieria splendens) grows leaves quickly after a rain to produce food through photosynthesis. In a few weeks, ocotillo flowers bloom, seeds ripen and fall, leaves drop, and the plant becomes dormant once more. Ocotillo stems also have a waxy coating to help conserve water during dormancy. Other perennials include brittlebush (Encelia farinosa), some varieties of California poppy (Eschscholzia californica), and desert paintbrush (Castilleja angustifolia), a parasitic plant that appropriates water from its host. By contrast, annuals, or ephemerals, germinate only after a heavy rain, and then complete their reproductive cycle very quickly to capitalize on optimal heat, light, and moisture conditions. They bloom profusely for a few days or weeks in the spring, and then die, leaving their drought-resistant seeds in the desert soils until the next spring rains. Annuals are responsible for the colorful desert wildflower displays that often appear in spring. Examples of such wildflowers are sand verbena (Abronia villosa), Mojave aster (Xylorhiza tortifolia), and dune evening primrose (Oenothera deltoides). Generally, thousands of annual and perennial seeds can be found in every handful of desert soil; the world record is over 200,000 seeds per square meter, though the Mojave’s soils contain far fewer.
 
Photo of ocotillo plant.
Photo of Mojave wildflowers.

Native Americans used the red, tangy-sweet blossoms of the ocotillo plant to make a beverage similar to lemonade.

DORAN SANCHEZ, BLM

Mojave Desert wildflowers such as these four o’clocks are alluring not only because of their extravagant beauty, but because of their rarity and unpredictability. After sufficient quantities of winter rain, sandy flats and lower hillsides throughout the desert may be carpeted with many different varieties of flowers in the early spring, with a second flowering possible after late-summer rains.

BLM RED ROCK CANYON NATIONAL CONSERVATION AREA


 Animals

Desert animals are more susceptible to temperature extremes than are desert plants. Animals receive heat directly by radiation from the sun, and indirectly by conduction from the substrate (rocks and soil) and convection from the air. The biological processes of animal tissue can function within a relatively narrow temperature range called the range of thermoneutralitThe Mojave Desert is an environment of extreme heat, poor soil nutrients, limited soil water-holding capacity, and—worst of all—little water. Even when rains come to the Mojave, often a great amount of water falls in a very short time onto ground so dry that the rain runs off quickly, washing away skimpy desert soil in the process. Sometimes, high temperatures cause rain to evaporate before it reaches the ground. Wind frequently compounds these challenges by rapidly evaporating scarce moisture and covering plants with dust. Luckily, the Mojave’s plant and animal species have developed ingenious physiological and behavioral adaptations that allow them to thrive in such a harsh world. Here are some examples of the complex ways in which Mojave species have adapted.

Photo of zebra-tailed lizard.

The extremely swift zebra-tailed lizard (Callisaurus draconoides) is easily identified by its prominent black-striped tail, which it waves to distract predators.

BLM RED ROCK CANYON NATIONAL CONSERVATION AREA

Some animals, such as owls and bats, are active only at night when temperatures are lowest. Animals that are active in early morning or at dusk, such as lizards, snakes, rodents, and insects, seek shelter in cool, moist burrows during the heat of the day or hide themselves under rocks or bushes. Birds such as eagles can literally rise above the heat, finding cooler temperatures by flying high above the surface. Still other species, most often birds, migrate to cooler climates for the hottest portions of the year, returning to breed in the Mojave when temperatures are lower.

There is also a desert equivalent to hibernation, called estivation. For example, during hot dry spells, the spade-foot toad (Scaphiopus sp.) covers itself with a substance to stay moist and then enters an underground burrow, where it can survive for many months until heavy rains signal it to wake. After mating and laying eggs in temporary pools, the toads return to their burrows and resume estivation until the next heavy rains. The desert tortoise (Gopherus agassizii) also estivates; it eats cacti, grasses, and wildflowers from March until June, and then retreats to an underground burrow for the heat of the summer. In the cooler fall, the tortoise emerges to eat and drink. Some desert squirrels and spiders also estivate in response to food scarcity.
Photo of desert tortoise.

The adult desert tortoise’s hard shell and thick skin protect it from dehydration as well as from attacks by predators.

ROSS HALEY, U.S. FWS

Owls often gape open-mouthed and flutter their throat area to cool themselves by evaporating water from the mouth cavity, and vultures sometimes expel urine onto their legs to cool themselves through evaporation; however, these two approaches are only practical for animals that receive plentiful supplies of water from the prey they consume.

Some Mojave animals have developed special physiological structures to enable them to regulate body heat. Mule deer and jackrabbits, for example, have large ears that are densely lined with shallow blood vessels, allowing air to cool their blood as it circulates. Some small creatures, such as beetles and lizards, reduce the amount of heat they absorb from the desert surface by having long legs to keep them high up and to disperse heat. Pale-colored fur and feathers help others to keep cool by reflecting sunlight.

Photo of kangaroo rat.

The kangaroo rat excavates labyrinthine underground galleries where it lives in cool comfort during hot desert days.

GEORGE HARRISON
U.S. FWS

Mojave animals also have many different approaches to obtaining and conserving water. Some rodents and insects get water by consuming cacti and other plants, and bats obtain it by eating insects. Snakes ingest water when they consume prey animals such as rodents and conserve it by excreting metabolic wastes as solid uric acid rather than liquid urine. When there is no outside water available, desert tortoises are able to reabsorb the water stored in their bladders.

It is even possible for some animals, such as kangaroo rats (Dipodomys sp.) and pocket mice (Perognathus sp. and Chaetodipus, sp.) to get water by using dry seeds. They store the seeds in their burrows, where the seeds absorb moisture from the air; the animals then receive that moisture when they eat the seeds. Kangaroo rats are even able to manufacture water as a byproduct of chemical processes involved in their digestion of seeds, and they seal their burrows to recycle the moisture released during breathing. These creatures are so efficient in their use and conservation of water that even in captivity they will not drink water when offered it.
Photo of desert bighorn sheep.

Desert bighorn sheep are the largest native mammals in the Mojave Desert, with mature rams sometimes reaching 115 kg in weight. These amazingly surefooted animals have been known to leap 10 m down a steep incline and land with perfect accuracy.

BLM RED ROCK CANYON NATIONAL CONSERVATION AREA

The desert bighorn sheep (Ovis canadensis) is an example of a Mojave animal that is somewhat reliant on springs, rivers, puddles, and other outside sources of water, since it receives limited moisture from the food it eats and has developed no special accommodations in this regard. This is especially true in winter when vegetation is dormant and dry. Reliance on outside sources of water means that the bighorn’s territory, and that of most other large desert mammals, is limited by distance from such water sources.

 

 

 



Did you know that ...

  . . the Creosote Bush (Larrea tridentata) produces an antibiotic against staphylococcus, diphtheria, and typhoid bacteria?

 . . . the roots of the Coyote Melon (Cucurbita palmata) were used by Native Americans as a source of soap?

. . . during World War I, 7.2 million metric tons of burlap were made from the leaf fiber of Mojave Yucca (Yucca schidigera)?

 . . . Pickleweed (Allenrolfea occidentalis) grows in water that is six times saltier than ocean water?

 . . . the stem sap of the Rubber Rabbitbush (Chrysothamnus nauseosus) contains almost three percent rubber?

 . . . early Mormon settlers named Yucca brevifolia the “Joshua Tree” because they thought it appeared to be lifting its “arms” to heaven, like the biblical prophet Joshua?

 . . . the Rock Nettle (Eucnide urens) is covered with stinging “hairs” so formidable that bats have reportedly impaled themselves on plants growing outside cave entrances?