How a tree grows

Most trees, but not all, begin their life as a seed. When conditions are right, the seed will sprout, sending its first shoot upwards and a downwards root at the same time. When the first green leaves appear, they use photosynthesis to make the food supply for the tree from the sun’s energy, water and nutrient from the soil and carbon dioxide from the air. During this process, the leaves give off oxygen and water vapour.

The young tree continues to grow up and out by adding cells to the tips of the branches and to the outer layers of the trunk. (The trunk and branches do not grow longer by ‘stretching’ – a point on the trunk of a tree 1m above the ground will remain 1m above the ground for the life of the tree).

As new cells are added, the trunk and branches grow longer and thicker. These very special cells form the vessels called the xylem and the phloem that carry the water and nutrient throughout the tree.

The xylem carries water and nutrient up from the roots and the phloem carries food made by the leaves to all parts of the tree including down to the roots.

Between the xylem layer and the phloem layer is the cambium which has the job of producing the cells for the xylem and phloem. New layers of cells are produced each year, giving the familiar ‘rings’ that become evident when a tree is cut down.

Old phloem cells form the bark of the tree which plays the vital role of protecting the cambium.

Tree roots grow in a similar fashion – by adding cells to the tips and outer layers. Fine hairs near the tips of roots absorb the water and nutrient from the soil. Most trees have root systems that extend beyond the canopy of the tree and most of the roots of most trees are in the top few centimetres of the surface of the ground.

Trees are the basis of sustainable life on earth.