DESERTS By: Rakin Zuha Shaim Eashal

INTRODUCTION OF DESERT. A desert is a isolated area of land where little rainfall occurs and so living conditions are unfriendly for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of destroying the ground. About one third of the land surface of the world is arid or semi-arid. This includes much of the polar regions where little precipitation occurs and which are sometimes called "cold deserts". There are a number of ways of classifying deserts including by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by the geographical location of the desert.rainfallarid

HOW ARE DESERTS FORMED? Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces.weathering Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down and the sand grains break in pieces until they are a uniform size. The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur.dust stormsplainsmosaicdesert pavementserosionaquifersoases

MAJOR DESERTS Deserts take up about one third of the Earth's land surface. Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Polar deserts (also seen as "cold deserts") have similar features, except the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98% thickcontinental ice sheet and 2% barren rock). Some of the barren rock is to be found in the so-called Dry Valleys of Antarctica that almost never get snow, which can have ice-encrusted saline lakes that suggest evaporation far greater than the rare snowfall due to the strong katabatic winds that evaporate even ice.saltEolian processesrainAntarcticacontinentalice sheetDry Valleyssaline lakeskatabatic winds

DESERT ECOSYSTEM Though a desert may seem like a barren land devoid of life forms, life does exist in this harsh environment. Numerous plants and animal species have adapted to these seemingly unsuitable conditions. Out here, climate is a deciding factor for the existence of life forms. The temperatures can reach up to 115°F during the day, and come down to 32°F at night. Such extreme temperature makes it difficult for life forms to survive in the deserts, unless they adapt to this harsh climate. Surprisingly though, many plants and animals have adapted themselves to this climate over the years, and have become an important part of this ecosystem.

DESERT ANIMALS Deserts are home to a number of species of kingdom Animalia. Biodiversity of the deserts is as unique as other biomes of the world. You might not see these animals as you see zebras and wildebeests in Africa, but they do exist and each of these species play a crucial role in the desert ecosystem food chain. Like in most of the other ecosystems, plants are the primary producers, while rodents, insects and reptiles which feed on these plants are the primary consumers. Then come the secondary consumers, who mainly comprise larger reptiles and insects which feed on primary consumers. At the top of the desert food chain are the apex predators in the form of birds and mammals.biomes Animals found here include the Gila monster, chuckwallas, desert tortoise, rattlesnakes, hawks, ostriches, bobcat, kangaroo rats, mountain lions, etc. Most of these desert animals are nocturnal, i.e. active during the night, and spend the entire day burrowing. This adaptation helps them to fight the soaring temperatures that persist during the day. Water being scarce in deserts, these animals have also modified themselves to make the most of the available water. Some animals absorb water from plants, while others store it in their fatty tissues.

VEGETATION IN DESERTS When we talk about desert vegetation, most of us only think about cactus. However, we fail to understand that within cactus, there are different types which grow in different deserts of the world. These plants have modified themselves to sustain in the desert environment. Some plants store water in the specialized tissues, while others have small leaves with hair like structures which reduce the evaporation of moisture. In North American deserts, barrel cactus is the most abundantly found cacti species, while other species include crimson hedgehog cactus, pancake prickly pear cactus, saguaro cactus, etc. Other cactus plants such as brittle bush, saltbush, creosote bush, desert ironwood, gravillias, Joshua tree, Mojave aster, Soaptree yucca, hanging chain cholla, etc., are also quite common in deserts. All the deserts of the world put together may not boast of biodiversity at par with the rainforest or the grasslands, but they do boast of species with amazing adaptation skills. If it were not for all these species armed with exceptional adaptation techniques, the deserts would have had been actually vast barren stretches of land devoid of life.

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