Deserts cover about one fifth of the earth's land surface. There are actually four major types of desert. The deserts known as the hot and dry deserts are found close to the Tropic of Cancer and the
Tropic of Capricorn. They are much different from the cold deserts like the ones found in the arctic regions of the world. The semiarid deserts and the coastal deserts are scattered all around the globe.
But just what is a desert? There seems to be a wide range of definitions and guidelines the world over as to what is classified as a desert and which type of desert an area fits into. Generally speaking, a desert is any area that receives minimal rainfall, less than 12 inches per year. Let's explore these four types of deserts.
Hot and Dry Deserts
Hot and dry deserts are, well, hot and dry. Temperatures in the hot and dry desert vary between 20° C and 49° C (68° F and 120° F) depending upon time of day and other conditions. The soils in these deserts are rocky and/or sandy and may blow in the wind.
Because they are hot and dry, very few plants can live there. The few plants that do exist in a hot and dry desert are capable of conserving water. They have hard, thick coatings and some are covered in prickly spines to prevent water loss and to protect them from animals who might try to chew through them to get to their moisture.
Most animals in the hot and dry desert tend to be nocturnal or burrowing animals that can hide from the sun and its heat. Many can go long periods without water or can get water from their food.
The Missouri Botanical Garden provides a table which catalogues the features of some of the world's hot and dry deserts.
Cold deserts can be found in the Antarctic, Greenland, and other cold climate areas. Cold deserts are too cold to support much plant life. Mosses and lichens will grow in the springtime, and sagebrush and a few deciduous vegetation will make their homes here.
Precipitation is largely snow and the soils are often heavy and sometimes salty. Animals that live in the cold deserts are often burrowing animals that head underground to keep warm. Sometimes deer will find their way to the cold desert in search of food.
Semiarid deserts have the lowest amount of rainfall during the winter months. While the daytime can be relatively warm, the nights are much cooler. This cooling allows for the formation of dew which can be beneficial to the plants and animals.
Soil can be gravel-like or sandy in the semiarid desert and have less salt than soils of the cold desert. Plants may have silvery or reflective leaves to protect themselves from the sun. They may have spiny surfaces and a bad odor or taste.
Animals in the semiarid desert tend to burrow or stay in the shade of plants and rocks. Insects, small mammals, and reptiles live in the semiarid desert.
Coastal deserts tend to have mild temperatures that change gently between winter and summer. They are usually located along western ocean coasts where the wind blows and prevents the moisture from moving inland. There are no temperature extremes in these deserts as we might see in other habitats.
Soils have good drainage and are fine, textured and porous. Plants have the ability to store water so they have it for survival when rain is scarce.
Animals have developed adaptations for living in the dry environment. Some have developed the ability to slow their life cycles while others speed up their life cycles in order to improve survival. For example, some insects lie dormant for long periods until environmental conditions improve.
One thing to consider is that even within a specific type of desert, there are variations in the temperatures, the amount of rainfall, and the plants and animals that live there.
Some deserts even have an area known as an oasis. An oasis is a fertile area within the desert borders. Natural underground springs feed a region and provide the moisture necessary to give life in an otherwise desert environment.
The United States has four major desert areas: The Great Basin, The Mojave, the Sonoran, and the Chihuahuan. All four are located in the western part of the United States. The Great Basin Desert is considered a cold desert, while the other three are hot and dry deserts.
Southern Idaho is a sagebrush steppe desert, which is part of the Great Basin sagebrush desert that also covers much of Nevada and Utah, northeastern California, southeastern Oregon, and western Wyoming. This desert is the largest of four in North America, much of it above 4,000 feet in elevation.
It is a cold desert characterized by cold winters and hot summers. While snow is a common sight in the winter, overall moisture is limited to about 4–12 inches a year. Miles and miles of sagebrush and wildflowers such as sunflower and yarrow blanket this part of Idaho.
The Great Basin Desert covers an arid expanse of about 190,000 square miles and is bordered by the Sierra Nevada Range on the west, the Rocky Mountains on the east, the Columbia Plateau to the north and the Mojave and Sonoran deserts to the south.
How Desert Plants Survive
How do desert plants save water? Desert plants work hard to make use of what's available. They use the sun's energy to convert carbon dioxide (CO2) and water (H2O) into sugar, a process called photosynthesis. During this process, stomata on a plant's leaves and stems open to absorb carbon dioxide from the air and in return release oxygen. Each time a plant opens its pores, some water escapes. This is called transpiration.
Replacing this lost water is not easy with so little annual moisture, and if the water cannot be replaced, the desert plants will die. So desert plants have acquired special adaptations that help them reduce water loss. Here are some of their adaptations:
Smaller, fewer, and deeper pores — Many desert plants have smaller, fewer, and deeper pores than other plants. With such pores, hot and dry winds are prevented from blowing directly across the pores and evaporating so much of the plants' water.
Waxy cover — Plants not only lose water through their pores, they also lose it through the cell walls on their leaves. The leaves and stems of many desert plants have a thick covering that is coated with a waxy substance, allowing them to seal in and protect what moisture they already have.
Nocturnal — Plants typically lose a large amount of water through transpiration, especially on hot, sunny days when they are doing photosynthesis like crazy. So if transpiration occurs during daytime hours, high temperatures can cause water to evaporate quickly. But if the process occurs at night, less water is lost. Often times, desert plants do not open their pores until the sun goes down and temperatures fall.
Little leaves — Most desert plants have small leaves, spikes for leaves, or no leaves at all. The smaller or fewer leaves a plant has, the less water is lost during transpiration since it has less surface area open to the sun and wind. For desert plants with small leaves or none at all, the twigs and stems help to carry out photosynthesis.
Hide and rest — During the hottest part of the day many desert grasses and other plants “roll up” their leaves (hide and rest) to reduce the amount of surface area exposed to sun and wind. Some plants simply position themselves so they have less exposure to the climatic elements on a hot, sunny day.
Drop 'em in drought — Some desert plants grow leaves during the high moisture period of the year and then shed their leaves when it becomes dry and hot again. Such plants are called drought deciduous. These kinds of plants carry out photosynthesis only during the moist periods.
How Do Plants Get Water?
One way desert plants, trees, and shrubs suck up as much water as possible is by growing very deep taproots. Sometimes these roots can get to be more than 100 feet long. The above-ground parts of a plant may remain small for years simply because the plant puts most of its energy into developing its taproot system.
Desert plants may have a huge, tangled network of shallow roots that spread out from the plant in all directions. The roots can be as long as the plant is tall, allowing the plant to quickly absorb water from the slightest rainfall.
Why Do Plants Shrink and Swell?
Desert plants can soak up water, store it, and prepare to use it during drought. For example, cacti and many other desert plants store water in their fleshy leaves and stems.
Desert plants may also have other adaptations for water storage, such as pleats or folds that will allow the plant to swell with added water when it can. The pleats or folds can almost disappear if the plant soaks up a lot of water; then the plant can shrink, and its pleats or folds can become visible again as drought sets in and the plant makes use of water it has stored.
Though many desert plants die to the ground during the hottest part of each year, the water they have stored in underground roots, tubers and bulbs will sustain them until the next moist period.
Why do plants grow hairs and spines? The hairs and spines that grow on desert plants help reduce moisture loss by breaking the effects of the wind. They also help to cast small shadows on other desert plants, which can protect them from the sun. The hairs and spines can even serve to reflect the sun's rays away from plants because of their shininess. Lastly, hairs and spines can help protect plants from hungry animal predators.
Why Do Plants Produce Special Chemicals?
Scientists believe that desert plants may produce and give off chemicals from their leaves or roots that keep other plants from growing nearby. It is thought that plants do this to reduce competition, especially when water is scarce.
Why Do Seeds Of Plants Sleep?
Some desert plants cope with the desert's dryness by not coping at all. As a result, during drought they are present only as seeds in the soil. For months, years, or even decades these seeds “sleep” to wait out the dry spell in a dormant state. When the right amount of rain falls and soaks into the soil, they sprout and bloom. When this happens the desert's dry brown landscape can quickly change into colorful fields of wildflowers, herbs, and grasses.
Most of these fast-growing desert plants do not last very long. So aside from having seeds that are adapted to drought, they have few or no special adaptations to desert conditions. This is why desert plants of this kind sprout, flower, and leave behind a generation of seeds as quickly as possible. Short-lived desert plants like this are called ephemerals. With little water available to help them grow, dormant ephemerals are covered and protected by natural chemicals called inhibitors. The primary function of inhibitors is to keep seeds from germinating until enough moisture and specific temperatures are present. Once the inhibitor has been washed off, the seeds can sprout.
Today there are some plants found in the desert that do not belong there. These plants are misfits and do not benefit the ecosystem in which they were introduced.
Idaho is no different. It, too, has its share of misfit plant species. These plants species are referred to as exotic, alien, or non-native species and were introduced from other continents or regions such as Africa, Asia, Australia, Europe, India, the Mediterranean area, South America, and Russia.
Many exotic plant species were introduced intentionally with the idea that they would serve a great purpose and provide excellent benefit to all who used them, for example, shade trees to control wind and erosion, forage crops to support livestock, other plants to improve watersheds or beautify landscapes.
In other cases, alien plant species were transported and introduced unintentionally through immigrants and their belongings, or with imported goods. Regardless of how they arrived, as the years have passed since their introduction, we have realized that many of the introduced non-natives are more of a problem and threat than a benefit.
The most prominent desert misfit in the West is cheatgrass. Cheatgrass was introduced into the United States from Eurasia with the idea it would be a great food source for livestock and wildlife. That is true in early spring before its seeds emerge, but it is practically worthless throughout the remainder of the year.
Cheatgrass is a hardy plant that has no natural consumers in North America. So it can grow out of control. This disturbs the natural balance and crowds out native plants that are necessary for the native animals that need them for food.
Not only that, but cheatgrass, once dry, is a great fuel for fire. When wildfire starts in a sagebrush-dominated plant community, fire kills the sagebrush, but the cheatgrass can often survive and out-compete other native plants for important nutrients and moisture.