- live vascular tissue in a ring just below the bark.
- sapwood
- heartwood
Tree morphology: internal
Understanding the internal structure of a tree is an important part of understanding tree growth and health. The internal tissues of the tree provide structural support and transport water, minerals, sugars and other chemicals throughout the tree. This transportation system extends from the roots, through the trunk, into the branches and then the leaves. If this transportation system is damaged, the tree suffers.
The tissue is made up of microscopic cells that act like straws to transport water and materials up and down the stem. It is called the vascular tissue and is composed of xylem and phloem cells. Xylem cells transport water and minerals from the roots up to the leaves. and phloem cells transport sugars made by the leaves and other chemicals up and down the stem.
In conifer trees and angiosperm dicots (broad leaf flowering trees), this tissue is located all the way around the tree just under the bark. If the vascular tissue is killed by crown rot, invasion by a fungus that clogs the cells, or a boring insect such as a beetle that gets under the bark and eats up the vascular tissue, the tree can die.
The living vascular tissue made up of xylem and phloem cells is just under the bark. The center of the tree trunk is made up of dead xylem cells that act as structural support to keep the tree up. When you build something with wood from the lumber yard, you are building with dead xylem.
In some trees, such as our native coast redwood, the tree deposits chemicals in the center of the tree. These chemicals discolor the wood and also provide the wood with protection from decay producing organisms. Wood that is not impregnated with chemicals is called sapwood which includes the living xylem. The decay-resistant discolored wood is called heartwood. When you build a structure in the landscape such as a fence or deck that comes into contact with the ground, always use heart redwood because of its natural decay resistant properties.
