You might think that a plant could not possibly survive in the harsh conditions of the desert since it lacks moisture for such a long time during the year. But this isn’t true — many types of plants can grow in the desert because they are able to absorb water from deep underground aquifers.
These aquifers are like natural reservoirs filled with water that has been trapped under layers of soil or rock over millions of years. The deeper the water goes, the drier the surrounding area becomes. It’s only at the surface that the water gets any significant amount of oxygen, which makes it unsuitable as food for most organisms on land. Plants use their leaves to take up nutrients from the air. Their roots go down into these shallow-water reserves, where there is no competition between them and other life forms. For example, if you dig around in an Arizona sand dune, you’ll find some pretty healthy-looking cacti. These plants don’t need much water to live in the desert — their roots simply tap into the deep water supply below them. In fact, some species of desert trees actually die off after heavy rainfalls, while others flourish after each new storm.
This ability to thrive without getting too wet may help explain how certain plants evolved in arid environments. Some scientists believe that early plants were small and had poor root systems, growing short tendrils that hooked onto nearby objects. This made sense in the beginning, but today’s larger plants would benefit from having more extensive root networks, especially in areas where rainfall is scarce. By developing longer, stronger roots, plants can reach deeper into the ground and pull out mineral salts stored in the dirt. They also suck up tiny amounts of water through their cells instead of relying on the surface layer.
A similar adaptation occurs among animals living in hot deserts. Many mammals, including squirrels, rabbits, camels, foxes and coyotes, form burrows for protection. Since digging holes takes energy, animals will naturally try to stay away from open areas. If they dug aboveground, they’d be exposed to predators like hawks. So they hide underground, where they’re safe from the elements.
Plants and animals both adapt to extreme climates by taking advantage of water resources in the environment. You can see evidence of this process every day. When you drive along a highway through the desert, watch how often you spot roadside signs advertising “water” or “toilets.” Water wells are usually built near cities so people can access clean drinking water. And toilets? Well, we already know what happens when nature calls outdoors!
On the next page, learn about another key factor that allows plants and animals to live in the desert.
Desert Adaptations: Heat
One problem many desert dwellers face is high temperatures. During the hottest months of summer, the daytime temperature in Phoenix, Ariz., regularly reaches 100 degrees Fahrenheit (38 Celsius). With little shade to escape the sun, animals and plants must look for ways to cope with the heat. One common strategy is to become dormant during the hottest part of the day. Trees slow their growth rate until cooler times of the afternoon arrive; flowers close their petals until night falls. Animals hibernate during the warmest season.
But for those who choose not to wait out the heat, there are several adaptations to help them endure scorching days. First, all plants produce antioxidants called pigments to protect themselves against free radicals produced by sunlight. Second, different types of bacteria release chemicals called volatiles that make the air feel cool and calm. Finally, many species of desert birds sleep through the day and wake up once nighttime arrives, allowing them to rest throughout the hottest hours.
In addition to these strategies, animals and plants employ other methods to deal with extremely hot weather. Most reptiles, for instance, secrete a substance from glands located behind their eyes called a geothermal gradient. As creatures walk across the landscape, the difference in temperature creates a flow of fluid through channels within the earth. Geothermal gradients allow lizards to keep cool. Other animals seek shelter in shady spots, either low lying vegetation or caves, to avoid direct sunlight.
During the coldest nights of winter, however, animals and plants must adjust to warmer temperatures. Unlike in summer, when the days start out chilly, evenings in the desert are mild. Desert animals spend the colder months resting, digesting food and recovering from the effects of activity in the heat. Squirrels and chipmunks hunker down during the day and sleep through the night. Birds also practice torpor, entering a state of suspended animation during the late afternoon and evening. After sunset, they emerge to feed and mate.
Adaptation is a two way street — animals and plants also depend upon certain environmental factors to survive. On the next page, we’ll explore one particularly important aspect.
Desert Adaptations: Cold
While it’s easy to imagine desert regions as lifeless wastelands, the truth is far less bleak. The intense heat and lack of rainfall create perfect breeding grounds for mosquitoes and other insects. However, the absence of water does mean that many species of animals cannot drink standing up. Desert dwelling birds must perch on high rocks or branches to quench their thirst. A few lucky animals, such as badgers, camel spiders and snakes, can lay eggs underwater. Still others, like small rodents, have special organs that allow them to store water in their stomachs.
Water scarcity means that humans need to build infrastructure to bring fresh supplies to the desert. To accomplish this, engineers construct pipelines to transport water from rivers, lakes and streams thousands of miles away, then pump it hundreds of feet underground using electricity generated by solar panels. Once underground, the water flows through pipes and lines that connect to taps in homes and businesses. People carry out irrigation duties using sprinklers and drip hoses.
If you’ve ever visited the Grand Canyon National Park in southern Utah, you’ve seen just how vital water is to the region. Nearby towns rely on the Colorado River to irrigate crops and sustain wildlife. While the river appears tranquil and serene, its waters contain plenty of sediment and pollutants. The river was once a vibrant ecosystem teeming with fish and aquatic life. Today, however, the canyon is nearly empty of wildlife except for a few species of birds and amphibians. Scientists say the main reason is pollution.
For many parts of the world, water is becoming increasingly scarce, making survival in the desert seem impossible. However, even though many ecosystems have lost their biodiversity, there are still places where unique species exist. Much like plants and animals, human beings have adapted to the severe conditions found in the desert. We have learned to develop better ways to extract water from the ground, and we have learned how to survive without showers. Next time you visit the grocery store, check out the selection of bottled water. Chances are, you’ll notice a surprising variety of flavors available. The same thing probably applies to soda pop. Why waste your money on sugary drinks when you can enjoy something refreshingly tart from a bottle?