How do Tree's Grow?

WV State Capitol Complex

Redwood

Trees are the only terrestrial organism that are able to counteract the effects of gravity. Trees can reach as high as 400 feet in some places, which is about the height of a 33' building. To place this in perspective using the West Virginia State Capitol (292) versus the Redwoods of California (369'). Redwoods (Sequoiadendron giganteum) are taller than any building within West Virginia.

Trees grow in two ways: primary growth and secondary growth. Primary growth occurs in the roots and shoots (new growth) by increasing the height and length. Secondary growth increases the diameter of the trunk, stems, and branches. My focus in this blog will be the secondary growth and how a tree increases it diameter to eventually be used as saw timber. These two types of growth only pertain to deciduous trees and not coniferous.

First some basic vocabulary.

• Phloem: Located within the heartwood that is a vascular tissue that transports sugars from the leaves to the rest of the tree. This could be the roots or branches below.
• Xylem: Located within the sapwood that is also a vascular tissue that transports water towards the top of the tree. The reason this takes place is due to the bonding of water molecules (hydrogen bonding).
• Cambium: They are the stem cells of the tree that are able to form the tissue of the sapwood and heartwood.
• Sapwood: The younger most outer part of the tree that contains the nutrients needed for the tree survival.
• Heartwood: Located within the tree surrounded by the sapwood. This is where lumber and firewood come from. Generally the cells within the heartwood are dead and the vascular tissue is no longer in use except for storage.

Secondary growth begins with the cambium going through mitosis to eventually produce the cells needed for the tissues of the xylem and phloem. If the xylem is injured beyond repair then the tree will be cut off from the water supply, which in turn would shut down photosynthesis and the tree will die. This growth is only increasing the girth of the tree and not the height/length.

The first growth period takes place during late spring and early summer where a light color ring is produced. The final ring for the year is produced in fall and it is darker in color because of the slow growth and smaller cell sizes that are produced. By observing the width of the ring one can determine the optimal growing season for the tree when there was plenty of water and other resources. This can also determine if there was any damage to the tree due to environmental or human causes.


Link

Trees of Texas: How Trees Grow - Gives a simple understanding on how trees grow during primary and secondary growth. Also offers K-8 lesson plans on how to integrate the content offered in the website.