Living in the Desert
A beautiful and fragile place
When I first told friends that I was moving to Utah, they thought that I was crazy. I received the usual comments. My skeptical friends said, "There isn’t anything there but mountains and Mormons." My practical friends wondered "Where will you get coffee?" I told them that I was moving there for the deserts. They they knew that I was crazy. "You grew up in the Pacific Northwest. You lack skin pigment; you’ll burn to a crisp. What will you do?"
They had the usual desert concepts of the searing heat and endless sands of Lawrence of Arabia. So, since I am sort of a science geek, I decided to try to inform my friends. I began by looking up "desert" in the American Heritage Dictionary, which defines a desert as "a region rendered barren or partially barren by environmental extremes." Barren is defined as "lacking vegetation, especially useful vegetation."
I found it odd that deserts were defined by a lack of "useful vegetation". What is useful vegetation, but plants which are good for humans to use, and usually abuse too? Growing up in the Pacific Northwest I knew the clear-cut fate of such plants. Perhaps desert dwellers are fortunate in this definition.
We have further corrupted the meaning by using the word as a metaphor for a void. A desert of sensation. A desert of knowledge. This has had dire effects, as this corruption and misconception of deserts has percolated into the minds of waste managers, who believe that they can harmlessly dump their nuclear waste and garbage into the ‘barren’ deserts of the American Southwest.
How then to define a desert in less anthropocentric terminology? Early scientists described a desert merely as a place having an average of ten inches or less of precipitation per year, but Tucson, Arizona, averages more than ten inches of rain annually, and some grasslands average less than 10 inches of annual precipitation. Definitions are never that easy in the natural world; too many factors contribute to an ecosystem to make such a simple declaration.
One key to moisture lies in the unpredictable nature of when, where and how much falls. Moab averages 7-9 inches of precipitation per year, which usually falls as winter snows, when many plants cannot utilize the water, summer thunderstorms, when much of it washes away, and in spring showers, when it has maximum absorption and use by plants. If it rained here on a consistent basis Moab would be a much greener place.
Deserts are lands of extreme temperatures. The generally clear skies and sparse, widespread vegetation allow an estimated 90% of available sunlight to reach the earth’s surface, compared to 40% in more temperate zones. At night, the lack of moisture in the air reverses the process and 90% of the heat escapes. These effects combine to create vast changes in temperatures on both a daily and yearly basis.
A further clue lies in the effects of temperature on the availability of water. Throughout the day moisture can escape back into the air from plant transpiration and soil evaporation. This process of evapotranspiration is so successful in the desert that areas that receive as little as five inches of precipitation may lose 120 inches of moisture back into the atmosphere per year. This places plants under extreme stress, thus, even small changes in their environment may create drastic problems.
All of these factors regulate desert organisms. Water and its inconsistent availability is the limiting factor in desert biological processes. Water determines where plants and animals live, when they reproduce, and what they consume. Plants and animals must be excellent water conservationists in the desert as every drop is necessary. Observe the desert in springtime and watch the abundance of life that flourishes with spring rains and you will discover the importance and beauty of water.
Knowing how to define a desert doesn’t explain why they exist. What produces these zones of aridity? Warm air absorbs and retains moisture. Cool air releases moisture. This simple phenomenon bears the primary responsibility for desert formation. Whether the air temperature is controlled by air currents, water currents or mountain ranges the effects are the same; moisture is removed from a region, leaving a desert.
Global air circulation patterns produce a region of dryness between 15° and 35° latitude, north and south of the equator. Warm air rises at the equator, cools, releases its moisture and moves towards the poles. As it approaches the 30° parallels the descending air begins to heat up and increase its ability to retain moisture; like a giant sponge it sucks the earth dry. This phenomenon is the primary factor in producing the Sonoran desert.
Global water circulation can also affect air temperature. Cold ocean currents travel away from the poles alongside continents. As air moves over this water, it is cooled, decreasing its water retention ability. Thus when it reaches land the air may produce mist or fog but rarely rain. The driest spot on earth, the Atacama Desert, is on the Pacific coast of Chile and averages as little as half an inch of rain per year.
A third agent of change is mountain ranges. As warm, moisture-rich air encounters mountains, it rises and cools leading to a subsequent release of rain or snow. By the time this air has climbed the peaks, it has lost most of its moisture, and descends to lower elevations as warm, evaporative air. The Sierra Nevada mountains block Pacific Ocean currents and produce the rain shadow responsible for the Great Basin desert.
A final, often overlooked, factor involves the critical role that humans play in pushing environments towards desertification. As we overgraze rangelands, overcultivate croplands, cut down forests, and waterlog and salinate irrigated lands, we remove the protective grasses and cryptobiotic soil crusts. This contributes to the desertification process in four ways: one, rain washes away instead of infiltrating into the ground; two, the albedo or reflectiveness increases, which decreases local rainfall; three, nutrients are removed through soil erosion; and four, plants can be poisoned by too much salt.
After living in the desert, I have come to learn many things. Maybe the most important is that this is a beautiful and fragile place. As in all ecosystems, desert organisms have evolved and adapted to fill a particular niche, but their apparent heartiness belies their fragility. Over the years many of my friends have come to visit the desert. Some still think I am crazy, but many of them now feel as I do: this is a special place.
Editor’s Note: As an FOB (Friend of Bugs), freelance writer David B. Williams, author of A Naturalist’s Guide to Canyon Country.
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The Desert Environment
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