How many layers are there in tree trunk?« Back to Questions List

A tree trunk acts as a pipeline system as well as a support. It has many layers each of which has its own function. A deep study of the layers of tree trunk would tell us how fast the tree’s growth was, whether the tree suffered any injuries and if so how long ago and many more information.

tree trunk 1

The outside layer called bark covers the trunk of the tree. It acts as a protection against diseases and insulation against injuries. The next layer from outside is the phloem. This lies just below the bark. This fibrous tissue transports sugar down from the leaves.
The third thinnest layer is called the cambium. This is the life giving part of the trunk as other cells come from this layer. When the cambium cells divide, the ones that grows towards the outside become phloem and those towards interior become xylem. Xylem carries water throughout the tree.

tree trunk

Then there is a layer called Sapwood. This sapwood transports water up from the roots. It is usually lighter in color compared to the last layer heartwood.

Heartwood is nothing but aged sapwood and central supporting pillar of the tree. Both sapwood and heartwood together form the xylem. Young xylem cells form the sapwood and older ones form heartwood. Most of the trunk is heartwood.

When an injury is caused due to fire, axe or storms, further growth of tree depends on how badly the cambium layer is damaged. Regardless of what has happened to the internal parts of a tree, a tree can grow as long as the cambium layer remains intact. Cells from the cambium layer around the edges begin to multiply and grow inward.


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