PHOTOSYNTHESIS AND TREE GROWTH

A tree, like all other green plants, is able to utilise basic raw materials and convert these into more

complex compounds such as sugars, starches and cellulose. A tree achieves this by a process known as photosynthesis, which involves the intake of water and mineral salts through the roots and carbon dioxide through the leaves and, in the presence of chlorophyll and sunlight, the manufacture of these into sugars, starches and cellulose. The breakdown of these and the loss of water from the leaves (transpiration) is known as respiration. There is a continual building up and breaking down of these materials.

As the concentration of sugar increases in the sap it loses water to give starch, a storage product
mostly found in the sapwood.

It is important to realise that sugar can be moved or translocated within the tree but starch, being
a solid, cannot be moved across the cell wall. When a tree requires to call on its food reserves of starch they are changed to sugars before they can be moved. A tree which loses its leaves cannot manufacture food and therefore draws on its food reserves of starch.

Wood is mainly cellulose, but does contain lignins and gum-like substances known as hemicelluloses. Cellulose is used in many industries producing paper, cardboard and explosives. When wood is distilled destructively, tar derivatives and methyl alcohol are produced.

A woody plant grows in height and girth, Growth in height occurs at the apical growing point of
the main stems and branches, and later these tissues are used for other structures. Growth in girth
takes place between the wood and bark for, if it occurred in the centre of the tree, the increase in
growth would cause splitting of the tree.