While irrigation was the key to turning the Magic Valley into an agricultural oasis, it didn’t take irrigation to provide the valley with a vibrant plant community. When the first settlers staked their claims in Magic Valley, they were not facing a lifeless moonscape; there were plants all around them. Local botanists have estimated that northern Utah and southern Idaho were mostly grasslands when the settlers arrived. Headless blue bunch wheatgrass, basin wild rye and western wheatgrass were in rich abundance until overgrazing by sheep and cattle weakened the grasslands — giving way to sagebrush and, more recently, cheatgrass.
Native trees in the area included bigtooth Maple, Utah Juniper, Grand Fir, Rocky Mountain Maple, Neat leaf Hackberry, and Ponderosa Pine. Then there were the herbaceous flowering plants. The profusion of forbs included little sunflower, stone seed, flax, lupine, yarrow and penstemon.
How did these and other plants evolve to not only survive but thrive in desert-like conditions? To understand strategies that plants use to handle drought, it is instructive to look at desert plants. Cacti and other succulents famously store water in their leaves and stems. These are the camels of the plant world. Prairie grasses, like those our early settlers found, can store water in their roots. Grasses also develop an extensive root system to adsorb soil moisture when it is available and then die back when water is scarce, thus conserving energy. The roots of switchgrass can extend up to 12 feet to tap available pockets of water.
Most desert plants have shallow roots that fan out within the top several inches of soil. When rain falls, it tends to be brief and dries quickly. An extensive lateral root system allows these plants to soak up rainfall quickly before it evaporates.
Other plants meet the water challenge by growing a long, vertical taproot that plunges down toward the water table. Mesquite trees set the standard. Their taproots have been detected 80 feet below the surface. Then there are plants like the Creosote Bush that have a double root system, combining extensive but shallow lateral roots with a deep taproot. The Creosote Bush remains one of the most successful of desert plants.
Desert plants face a challenge in managing photosynthesis. In photosynthesis, leaves play a central role. Chloroplasts in the leaves harness sunlight and use it to convert water and carbon dioxide into carbohydrate fuel to support their growth. Leaves also expel a lot of water through small openings called stomata which allow water to evaporate out and carbon dioxide to enter. The water loss is useful to the plant as it creates suction that pulls water and nutrients up from the roots to nourish leaves and branches. Where water is plentiful, this system works beautifully. In arid climates, such water loss can be fatal. Therefore, desert plants have evolved strategies to conserve their water. Many desert plants have small waxy leaves, small wiry leaves with little surface area or needles instead of leaves. Some, like the blue Palo Verde tree, take pressure off their leaves by also using their trunk and branches for photosynthesis.
Other desert dwellers called CAM plants have evolved an alternate method of photosynthesis. Such plants close their stomata during the daytime and open them at night to take in carbon dioxide. They use carbon dioxide to form malic acid. Then during the day, the malic acid breaks down, releasing carbon dioxide which is used during photosynthesis. Another drought tolerance strategy involves simply going dormant during a drought. Many trees shed their leaves during a dry spell, dramatically reducing water loss, and then regrow those leaves when rain returns.
Many plants rely on a strategy called drought avoidance. They die. The term annual refers to a plant that lives for only one season. Desert annuals are often called ephemerals, because they often complete their life cycle in a matter of weeks or months. Some desert ephemerals will go through five complete generations in one season.
Remember that nature’s goal is the survival of the species, not the individual. Ephemerals put their energy into producing many hardy seeds that will carry their DNA on to the next generation. When their seeds are dispersed, the parent plants die. Insects, animals and the wind carry those seeds to new fertile soil. The desert is filled with ephemerals. This explains why a random desert shower will often be followed by the whole landscape coming alive in a profusion of blossoms.
The challenges that plants face in harsh climates are daunting. As the poet Gerald Manley Hopkins put it, “For all this, nature is never spent,” and we are constantly reminded of nature’s prodigious adaptation and survival skills.