How do trees grow?

“But the truth is that all trees are carbon eaters. They grow from the air by drawing CO₂ into their leaves, and there, solidifying it to build their wood, bark and leaf tissues. Trees are congealed CO₂.” (Quote from Tim Flannery, The Weather Makers, 2007).

The process of photosynthesis allows plants to use energy from sunlight to convert carbon dioxide from the atmosphere into basic sugars. These sugars can be assembled into cellulose, the major component of plant cell walls, thereby enabling tree growth.

All trees start life as a seed. Seeds only germinate under specific environmental conditions suited to each species (temperature and water are the usual triggers, while some native species require fire or other disturbance). Once germination occurs there is enough stored energy in the tiny seed to allow the first leaves to be produced. From then on, providing enough sunlight falls on the green leaves, the seedling begins growing into a tree.

Many eucalypts require fire to create suitable conditions for seedling germination. Other species do not need fire, such as many of the rainforest species that are adapted to grow in the dim light under a shady forest canopy. A canopy gap allows sunlight in, increasing the growth rate of trees in that spot, and can eventually grow up to fill the gap.

Other requirements are water and nutrients (from the soil system). Water is sucked up into the leaves through the xylem vessels; water loss from the leaf surface creates a tension in a column of water that extends from the roots, enabling water to be pulled upwards into the tree from the soil. This water is often full of dissolved nutrients that are vital for cell structure and the manufacture of cellular components such as DNA and chlorophyll.

As a tree grows it develops a vascular system (vessels that transport water and sugars around the plant) within the trunk, a ring of dividing internal cells that increase the trees girth as it grows (and gives the characteristic annual tree growth rings by which you can age some species) and the dead outer bark, which acts as a protective layer for the living tissue inside. In some cases, this bark protects the tree from fire (as in the thick stringy-bark) whereas smooth, gum-type bark may not be as protective and can in fact encourage bushfire spread when long, thin strips of loose burning bark break-free and are blown through the air to ignite new fires.