How trees grow
![Trees have a circulatory system for transporting water and food. Trees have a circulatory system for transporting water and food.](../../unit9_selecting_timber/images/how_trees_grow.jpg)
Trees have a circulatory system for transporting water and food.
The upward system is in the sapwood. Water and nutrients from the soil are carried up through the sapwood to the leaves, where the process of photosynthesis is carried out.
The downward system is in the phloem, or inner bark. This is where the sugars manufactured in the leaves are carried back to all the growing parts of the tree.
Trees grow by making food from the raw materials they extract from the soil and air. This process is called photosynthesis, because it uses the power of sunlight ('photo' meaning 'light') to process, or 'synthesise' the carbon dioxide from the air, water from the soil and various other nutrients also absorbed from the soil.
Photosynthesis takes place in the leaves. Air enters the leaves through thousands of tiny pores, and is combined with water and chlorophyll to produce glucose, a type of sugar. The glucose is then carried in the sap stream through the phloem to the growing parts of the tree. There it is converted into more complex carbohydrates, such as cellulose and starch.
Cellulose is the basic body-building material of plants, and the main component in wood. Food that is not used straight away is stored as starch.
Growing Parts
Trees grow in three directions.
- Up. The tree grows in height as its branch tips build new cells to make the branchlets longer. This is also where leaves and flowers are produced.
- Down. The root tips are where roots grow in length. Most of the water and nutrients are absorbed by root hairs, which start a short distance behind the tips.
- Outwards. The cambium layer makes the tree grow in girth. It is a thin layer in between the phloem and the sapwood. On the phloem side, it forms new inner bark, and on the sapwood side, it forms new wood tissue. We'll talk more about the role of the phloem in the next lesson: The Stem.
![Learning activity icon](../../shared/images/css_images/learning_activity_icon.jpg)
Learning Activity
Use your understanding of how trees grow to answer the following two questions. Share your answers with other learners in your group to see whether you agree on your reasoning.
If you have trouble answering the questions, you can do more research on the topic of growing trees at the Timber.org.au website, managed by the Forest and Wood Products Australia.
1. If you wanted to kill a tree by 'ring barking' it, all you would need to do is cut around the tree through the bark, deep enough to cut through the phloem.
Why wouldn't you need to cut all the way through the sapwood?
2. Let's say a tree is 10 years old and has grown to a height of 4 metres. You come along and hammer a nail into the trunk at 2 metres above the ground. 10 years later the tree has grown another 4 metres, and is now 8 metres tall.
How high will the nail be above ground level? Describe what the tree will have done to the nail.