How do Trees Grow? How Old are Trees – (Ring a ding ding)

Each year, a tree trunk expands in width. Once the tree trunk is cut down, you can see rings in the wood. These are called "growth rings".

Each ring consists of a dark and light band.

Every year, a tree grows larger in two primary ways: the expansion of its roots and stems, and the progressive thickening of its trunk. Unlike other living organisms like humans, trees can only create new cells in specialised places. The growth of a tree relies heavily on its environment and conditions.

Tree roots have a hard, probing root tip which seeks out sources of nutrition in soil, and behind them are tiny, hair-like fibres which entwine themselves around individual grains of soil to absorb moisture and dissolved minerals. Roots grow opportunistically, a tree will create more roots where conditions are more favourable; fertile, moist, and the soil is less compacted. In soil that is dry and compacted, a tree will create fewer roots, but they will be larger and capable to travel further away. If the soil a tree is growing in is shallower or restricted, roots can grow wider.

Tree trunks are critical to support the branches of the canopy and enable photosynthesis to power its search for moisture and sunlight. A tree’s diameter growth occurs in the cambium layer of the bark, which is comprised of living growth tissue cells, protected by the thick outer bark.

A tree trunk grows in layers, with each serving a very specific function:

1. Bark: A thick and robust outer layer, like our skin. It protects the trunk from damage.
2. Cambium: The layer between the bark and softwood, which makes new wood (sapwood)every growth cycle.
3. Sapwood: Softer, new wood containing the Xylem and Phloem (pipeline) cells, transporting water, nutrients, and energy.
4. Heartwood: Older sapwood that has been pushed further away from the sapwood’s nutrients, making it darker and harder. It cannot conduct water or nutrients anymore.
5. Heart: This is the centre of the trunk, comprised of dead and decaying wood.

Every year, Xylem and Phloem cells are formed, adding an additional layer, these layers are called annual/growth rings. These rings comprise both a dark and a light band. You can determine the age of a tree after it has been felled by counting how many times both bands appear on the tree stump.

The bark of a tree is very important to a tree trunk, and ultimately trees deteriorate and die due to damaged bark from insects, disease, and environmental damage (fire, wind, etc). The condition of a tree’s bark is one of the most important factors affecting its health.