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The Earth

About Vegetation Resources

The Making of the Landscape

Why are there different types of deserts, grasslands, and forests? A general answer to this question is the differences in climate which result primarily from differences in average temperature and precipitation caused by global air circulation.

The most important factors in producing tropical, temperate, or polar deserts, grasslands, and forests are the combination of average annual precipitation and temperature (together with soil type). On maps such as the one below, biomes (terrestrial regions with characteristic types of natural, undisturbed plant communities adapted to the climate of an area) are presented as having sharp boundaries and as being covered with the same general type of vegetation.

Vegetation Map

Climate and vegetation both vary with latitude (distance from the equator) and altitude (elevation above sea level). If one has to travel from the equator toward either pole, you will generally encounter ever colder climates and zones of vegetation adapted to those climates. Similarly, as elevation above sea level increases, climate becomes colder.

Plant Sizes and Shapes

Vegetation Picture

The plant communities found in various biomes have distinct physical appearances depending on the types, relative sizes and layering of their plant species (above). Climate and soil types also play a role in determining these characteristics.

Plants that are exposed to cold air year round or during winter need a design that keeps them from losing too much heat and water. For example, trees or tall plants would lose too much of their heat for survival in the cold, windy artic grasslands.

Desert plants exposed to the sun all day long must be able to lose enough heat so that they don't overheat and die. They must also conserve enough water for survival.

Tree in the canopies of wet tropical rain forests tend to be broadleaf evergreen plants, which keep most of their broad leaves year round. The broad leaves allow for them to collect ample sunlight for photosynthesis and also radiate out heat during the hot summer. In a climate with a cold (and sometimes dry) winter keeping such leaves would cause plants to lose too much heat and water for survival. In such climates, broadleaf deciduous plants, such as oak and maple trees, survive drought and cold by shedding their leaves and becoming dormant during such periods.

Further North, where summers are cool and short, this strategy is less successful. The evolutionary solution in such areas is coniferous (cone-bearing) evergreen plants (such as spruces, pines, and firs). These plants keep some of their narrow pointed leaves (needles) all year. The waxy coating and shapes and clusters of the needles of conifers slow down heat loss and evapouration during the long, cold winter. Additionally, by keeping their leaves all winter, such trees are ready to take advantage of the area's brief warm summer without having to take time to grow new needles.


©  Copyright 2002, 2003 Seelendran Naidoo
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