The next article in this series of Anatomy of a tree, will be focusing on the trunk and branches. It continues on from the first part: The roots. Having a good understanding of all these elements will help us to look after our trees and better understand their limitations.
Trunk and Branches
Trees have the more permanent structure of a trunk and branches. This is the main difference that separates them from plants. Trees having wood at their core are what makes them more resilient and helps give them their incredible lifespans.
Example of the longevity of trees in an ancient forest
The above-ground structure
When we look at the above ground structure of the tree, they all have the following elements.
- Bole – The area between the base of the trunk to the first branch.
- Trunk – the main structure of the tree, that the branches grow from.
- Branch – A part of the tree that grows from the trunk in generally a horizontal, upward direction. Large branches are known as bough and the smaller as twigs. The branches support foliage growth.
- foliage – A broad term meaning the leaves of a tree but can include needles (pine) and scale (juniper) like material. It is normally green.
- Crown or Apex – The top of the tree.
Key elements of a tree.
If we cut across a tree’s trunk, we will get an inside view of the different layers. Starting from the inside centre we will label these.
- Pith – the centre of the trunk and the initial provider of nutrients of where it all began; the sapling.
- Heartwood – central layers of dead wood that supports the trunk and branch structure, usually darker in colour.
- Sapwood – the outer layers of newer wood, which transport raw sap that is carrying nutrients from the roots upward through out the tree.
- Cambium – An outer growth layer that creates both sapwood and phloem, which in turn increases the tree’s thickness.
- Phloem (inner bark) – The next layer after the cambium tissue and before the bark. Its purpose is to move sap that has been transformed from leaf photosynthesis and that contains sugar, around the tree and back down to the roots.
- Bark – The outer layer that protects the tree and varies from species to species.
- Growth rings – Each year of growth creates a new ring of sapwood that is visible.
- Medullary ray (wood ray) – living cells that run across the growth rings, that allow the transportation of sap radially.
Cross section of a trunk
The definitions from the trunk cross section, give us a good idea of how nutrients and water are transported within the tree. We will take a more detailed look at this in the next and final part when we will be looking at the role of foliage.