Download Characteristics of a Biome. On a global scale, all ecosystems of one

Characteristics of a Biome.
On a global scale, all ecosystems of one type are referred to as a biome. An ecosystem is a
community of animals and plants treated as a unit with its physical environment. There are 9
biomes in the world such as tundra, mediterranean and temperate forest. The biome which I have
studied is the desert biome . There are numerous deserts throughout the world which include teh
Sahara desrt, Atacama desert and the Mojave desert.
A desert is defined as an arid region with little or no rainfall in which vegetation is scant or absent,
unless specially adapted or where groundwater conditions are favourable. The availability of
water is the main factor in determing what animals and plants can survive in a desert
environment. Not only do they have a low level of precipiattion, they have a strong tendency to
lose water through evaporation.
Desrts may be hot or cold, desrts are predominantly regions of boulders, gravel or bare rock with
only 10% of desrts sandy. Some desrts have potentially fertile soild that can be brought to a
productive state by irrigation. Some deserts are populated either seasonally by nomadic trives or
permanently.
Deserts can be catergorised into three categories, extremely arid (at least 12 consecutive months
without percipitation), arid(annual percipitation less that 250mm) and semi-arid(annual
percipitation between 250mm and 500mm)
Any of that above paragraph necessary??????!!!!!
The majority of desrts lie on the western magins or in the centre of continets between 15 and 30
degrees north and south of the equator. Some of these include the sahara and the Arabian.
Others luie between 30 and 40 degrees north and south of the equator. These include the Great
Basic and Mojave deserts in the U.S.
A number of factors lead to the formation of deserts, these include high pressure belts, rain
shadows, cold ocean currents and continentality. Most desrts are located in high pressure belts
between 15 and 30 degrees notrth and south of the equator. Air is heated at the equator and
rises which creates a zone of low pressure. As it rises it cools and rainfall results. This air moves
away from the equator and cools further before descending at about 30 degrees north or south of
the equator. Compression warms the descending ai to form belts of high pressure. Onj reaching
the earths surface, the air is returned towards the equator as part of the trade winds. These warm
air masses are able to hold more water vapour and the atmosphere becomes very dry. These
conditons along with the absence of surface water prevent cloud formatio nand precipitation. The
rain shadow effect is another cause of deserts. Coastal mountain ranges crate a barrier to the
movement of moist air, forcing it to rise. Precipitation occurs on the windward side and the air
descending on the leeward side is drier and warmer. This creates a rain shadow effect and in turn
a rain shadow desert.
Deserts suffer very ltitle rainfall but none are truly dry. When rain does full there is rapid run off.
Low leverls of infriltation and high rates of evaporation minimise its effectivness for vegeation
growth. The annual temperature range is between 20C and 30C. Diurnal range is often more than
30C. In contrast night temperatures are likely below 0C
The soils in tehse desrts are known as aridisols. They can from a sand and fine texture to a
gravelly and coarse texture. They have a minimum amount of sub surface horizon development.
Due to low percipitation and less intense weathering, aridisols tend to be poorl developed with a
higher content of mineral matter than organic matter. As a result they may not have an A horizon.
The absence of organic matter is the result of low plant productivity. Soils with a low content of
organic matter are unable to retain all the moisture that falls onto them. Thus intesnse
evaporation occurswhich tends to bring dissolved monerals close to the surface producing a
strongly alkaline soil. calcification is the dominant process. Nutrients that were leached down into
the soil are drawn abck up by capillary action A hardpan known as a caliche builds up in the soil,
making it almost impermeable. This impedes the growth of plant roots. Salinisation is also active
and the high surface content of sodium can lead to extensive saltpans where nothing can grow.
Deserts are characterised by having sparse vegetation. Along with soil the vegetation has to
adopt to the extreme heat. This vegetation has adopted in a numbe of ways.
1)Some succulent plants are able to sotre water in many different parts long periods of time,
these include roots, stem, bulbs an fruits. 2) Some plants including cacti have extensive root
systems close to the surface. They are radial and allow for quick acquisition of large quantities of
water. 3) Some plants have taproots allowing them to reach deep underground in search of
water.
Desert productivity is naturally low but high productivity of crops such as vegetables , fruits and
grains can be obtained with irrigation. Some desert areas once had reasonable amounts of
vegetation cover but were overgrazed by sheep and cattle.
There are few large animals in the desert because most are not capable of storing sufficient water
and withstanding heat. Like plants, animals have adapted to the harsh conditions in differnt ways.
The elf owl and rattlesnakke are nocturnal because it is cooler at night. Some bowwor
underground when it is too hot and then come out when it is cool enough, these include the
tarantula, desert tortoise and kangaroo rat. Many desert animals are paler than relatives in other
environments. This it so that they take in less ehat and are less conspicious to predators. The
jackrabbit has ears which are almost a quarter of its total body length. During hot conditions it
holds its ears upright and dialtes its blood vessels, this loses heat. When it is cold it keeps its ears
close to tis body. The road runner which is one of the most commong desert birds spends most of
its time running away from the coyote....(just kiddding) .......spends most of itss time on the
ground running because it requires less energy than flying....