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Silviculture / Treatment of Individual Trees / Tree Growth and wood production
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Tree growth and wood production

The above ground part of a tree essentially grows in two ways. Elongation of the main stem and branching is a result of cell division by the apical meristem at the growing tips. The corky remnants of this growth, known as the pith, can be seen in the stem. Thickening of the branches and trunk results from cell division by the cambium, a thin layer of cells hidden just below the bark.

Both wood and bark form from cambium growth. The newly created bark cells form the phloem through which the carbohydrates and hormones generated in the leaves flow down the trunk to the root system feeding cambium growth on the way. As new phloem cells are formed the old ones dry out adding to the protective bark. On the inside of the cambium, newly fashioned wood cells add to the sapwood through which the water and nutrients flow up the tree. The sapwood is also a place to store starch that is later used to sustain the tree through periods of slow growth or dormancy. Usually, as each new growth ring of sapwood is formed, an inner ring of older sapwood is retired with the cells filled with crystals or resins, becoming heartwood.

The type and number of wood cells produced by the cambium is determined by the concentration of carbohydrates and auxin (which is an important hormone for plant growth) both generated by the leaves. Following rapid shoot growth, high levels of carbohydrate and auxin cause the formation of large earlywood cells. When the levels drop off during dry or cool conditions, or as the trees enters a dormant phase, small thick-walled latewood cells are formed. It is the dense latewood cells that form the growth rings.

The different parts of a tree trunk.

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