Forestry

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Soils have supported trees for some 350 million years. In the years to the present there have been huge changes in the distribution and nature of forests, driven by changes in climate which also led to changes in the soils in which they grow. There was a time when the tree was the principal life form on earth. With the advent of humans, this has now changed but trees still cover a major part of the earth's surface and provide most of its biomass. The relationship between trees and the soil is an extremely important one. Trees rely on the soil for anchorage, for nutrients and for water; hence there would be few, if any, trees without soil. In turn, trees as well as other plants are an important factor in the creation of new soil as leaves and other vegetation rots down and decomposes.

Trees are perennial plants. A tree gets its sustenance from energy in the form of sunlight, carbon dioxide from the air, and water and nutrients from the soil. By a process called photosynthesis, organic compounds are created from water and carbon dioxide using light energy absorbed from the sunlight. Most of the water needed by the tree comes from the soil. The roots of the trees tap the soil water supply and this water is then passed up the trunk to other parts of the tree. Most of the nutrients required by trees are also taken up from the soil and passed dissolved in water to the growing tree via the roots. This process continues year after year as long as the tree remains alive, which may be hundreds of years. Did you know there are trees still alive that were alive back in the time of King Henry the Eighth!

Trees grow both in height and diameter. They grow in height by division of cells at the tips of their branches. The girth or diameter of the tree grows in a different way - by cell division in the layer between the bark and the main woody part of the trunk. The Californian Redwood (Sequoia sempervirens) is the tallest tree in the world, and can grow to a height of over 100 metres and have girth of 25 metres. This represents a huge biomass.

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