John Tyman's Cultures in Context Series EGYPT and the SAHARA www.johntyman.com/sahara |
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1.3 Plant and Animal Life : 049-063 |
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John Tyman's Cultures in Context Series EGYPT and the SAHARA www.johntyman.com/sahara |
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1.3 Plant and Animal Life : 049-063 |
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| .049. With high temperatures and strong winds, cloudless skies and low humidities, the little rain that does fall is quickly evaporated. Everything and everyone is threatened by dehydration. So the key to survival here -- the survival of plants, animals and human beings -- is the ability to obtain enough water, and to avoid losing it. The diversity of plant and animal species is inevitably limited, but they display a wide range of strategies for survival. (Wild melons on the Hoggar Massif) |
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| .050. Much of the central Sahara averages less than 20 mm annually. Most perennial plants simply cannot survive under these conditions. Such areas can only support annuals. These spring up after heavy rain, when the desert will briefly be green: but they will flower and seed quickly, wilt and die -- living on as seed lying dormant in the soil. (Plant in seed in the Tassili-n-Ajjer) |
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| .051. Some plants have thorns instead of leaves, offering a smaller surface area from which water can be evaporated. Others store the water that falls in the occasional thunderstorm. The Sahara lacks the cacti of American deserts, but it has comparable succulent species. And plants in shaded locations can survive on less moisture. (Flowering plant at foot of narrow steep-sided wadi in the Sinai) |
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| .052. Many annuals are able to adjust their size to reflect the amount of water available. When there is ample rainfall they flourish, but when the rains during which they germinated are followed by a long period without rain such plants adopt a dwarf form with fewer and smaller leaves, and produce fewer flowers and fruits. They also produce these in a shorter period of time than comparable species growing under wetter conditions. (After rain in the Tassili-n-Ajjer) |
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| .053. Though the surfaces of most desert soils are dry year-round (save for days following the occasional rains) there is often a damp layer within the soil profile and also water in the crevices of underlying rocks. Together they are capable of supporting a few perennials, though these may need to adapt to a high salt content. In the heat of the day, though, many plants will wilt, so that the surfaces of their leaves are no longer at right angles to the sun. (Stressed perennial near Ain Khudra in the Sinai) |
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| .054. Trees and shrubs are rare, found only where their roots can reach ground water, as in wadis occupied briefly by intermittent streams following rain. (Floor of wadi in the Hoggar after rain) |
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| .055. The tamarisk, or “salt cedar”, is the commonest species of tree found in the Sahara. It is evergreen and typically between 5 and 15 metres in height. Its presence is an indication that there is ground water to be found here at a depth of between 5 and 15 metres. (Tamarisk bluff near Ideles) |
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| .056. Falling water-tables threaten the survival of localized tree-covered bluffs like this, however, as do travelers hacking off branches, it being one of the few sources of firewood in the desert. (Near Ideles) |
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| .057. Acacias, too, are deeply rooted. In contrast the roots of succulents typically extend for only 3-4 cm beneath the surface so they can make the most of every shower even when the rain does not sink very far into the ground. (South of Illizi) |
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| .058. Most plants also collect water from a wide area and so are spaced far apart. Only in an oasis will you find areas of continuous plant cover: everywhere else plants are widely scattered. (North of In Amenas) |
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| 059. Animals display a similar range of adjustments -- to regulate their body temperature and/or conserve moisture. Some sleep underground throughout the.hot summer (much as some species hibernate in cold climates). Others only come out at night, so that by day the only signs of their presence are the tracks they leave in the sand. (North of El Oued) |
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| .060. The existence of animals is also revealed by their dung ... which is drier (and their urine more concentrated) than it would be in a humid environment ... and by their remains when they die. (Horn of gazelle north of Ghardaia) |
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| .061. Most desert mammals are light in colour: this means not only that their skin absorbs less heat, but also that they are less obvious to predators -- in an environment where there is little protective cover. Those that do move around during the day -- gazelles, camels, donkeys etc. -- usually move to shady spots in mid-morning and rest there till late in the afternoon. (Riding camels at Ain Khudra in the Sinai) |
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| .062. The reproduction of animal species is also influenced by the climate. Most gazelles here calve about a month after the onset of the rains, when plenty of grazing is available. Camels have a pronounced rutting season at the time of the rains and a pregnancy lasting twelve months. (Young camel courtesy: Puzzles-Games.eu ) |
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| .063. The fertility of jerboas and voles declines during dry weather and their population levels drop off accordingly: also no rodents here sweat. And lizards run between patches of shade with their body held high to reduce the rate at which heat is absorbed from the surface: and when they reach the shade they flop down to allow their body to lose heat by contact with the cooler ground. (Long-eared jerboa courtesy: 25.media.tumblr.com ) |
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