The diversity of deserts

Over the last few weeks, we've been featuring the different types of biomes of the world in this page. We have already spoken about two of them, and today we'll feature the third in the list of six biomes.

When you hear or see the word desert, what springs to mind immediately will be hot sunny weather, sand dunes all over the place and camels. But, did you know that the diversity in a desert biome is second only to that of a tropical rain forest? Amazing, isn't it? Although this may be hard to believe, it's the truth.

If your mother is a gardening enthusiast, check whether she has any cactus plants. A wide variety of cacti is available even at the numerous flower exhibitions. Where do you think all these plants originated? Yes, they are all from the desert biome.

Deserts cover about one fifth of the Earth's surface and occur where the annual rainfall is less than 50cm. There are two major types of deserts in the world; hot and dry deserts and cold deserts. There could also be two more sub-types, semi-arid and coastal.

Most deserts, such as the Sahara of North Africa and the deserts of south western United States, Mexico and Australia, occuring at low latitudes, are hot and dry deserts, while cold deserts occur in the basin area in the range of Utah and Nevada in USA, and in parts of western Asia.

Animals

Most deserts have a considerable amount of specialised vegetation, as well as specialised vertebrate and invertebrate animals. Soils often have nutrients because they need only water to become very productive, and have little or no organic matter. Disturbances are common in the form of occasional fires or cold weather, and sudden, infrequent, but intense rains that cause flooding.

There are relatively few large mammals in deserts because most animals are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are non-mammalian vertebrates, such as reptiles. Mammals are usually small, like the kangaroo mice of North American deserts.

When it comes to a hot and dry desert, the name itself implies what it is. Most deserts of this type don't have many plants. The only animals which can survive in this enviornment have the ability to hide under ground. This is because they would not be able to live too long, exposed to the hot sun and heat. They only come out in the night when it is a little cooler.

A cold desert is a place that has snow in the winter instead of just a few degrees drop in temperature, like it happens in a hot and dry desert. It never gets warm enough for plants to grow, with the exception of a few grasses and mosses.

The animals in cold deserts also have to hide away, but in their case, it's to keep warm, and not cool. That is why some of the animals found in the hot and dry deserts are seen here too.

Cold deserts are located closer to the Arctic Circle. The temperature in hot and dry deserts ranges from 20 to 25 degrees Celsius. The extreme maximum temperature for hot deserts ranges from 43.5 to 49 degrees Celsius. The temperature in cold deserts during winter ranges from -2 to 4 degrees Celsius and in the summer, 21 to 26 degrees Celsius.

The rainfall in the two types of deserts are different. Hot and dry deserts usually have very little rainfall and/or concentrated rainfall in short periods, between long rainless periods. This averages out to less than 15cm a year. Cold deserts usually have lots of snow. During the winters, there is very little if any rainfall; they also have quite a bit of snow during winter.

Vegetation

Vegetation is very rare in hot and dry deserts. Plants are almost all ground-hugging shrubs and short woody trees, with all leaves being replete (packed with nutrients). Some examples of these plants are Turpentine Bush, Prickly Pears and Brittle Bush.

In order to survive, all these plants need adaptations for that particular environment. Some of the adaptations in this case are the ability to store water for long periods of time and the ability to stand the hot weather.

In cold deserts however, the plants are scattered. In areas with little shade, about 10 per cent of the ground is covered with plants. Animals in the hot and dry deserts include small nocturnal (only active at night) and carnivorous animals.

There are also insects, arachnids, reptiles, and birds. Some examples of these animals are borrowers, mourning wheatears and horned vipers. Cold deserts have animals like antelope, ground squirrels, jack rabbits and kangaroo rats.

Compiled by Janani Amarasekara