The Anatomy of a Tree

Trees of different species vary greatly in size, shape and overall appearance. Generally, however, trees are comprised of the same basic components, with a root system in the ground anchoring a strong, vertical trunk that supports a crown of branches, twigs, and leaves. Here we examine these basic components of a tree and the functions associated with each:

1. Crown: The crown is the upper portion of a tree consisting of the branches, twigs and leaves. Crowns vary significantly among different types of trees. Crowns can range from condensed, cylindrical shapes to widespread, almost spherical shapes. The crown serves the vital function of displaying its leaves so that they may capture the energy necessary for photosynthesis, and also filters particles from the air and minimizes the impact of rain falling on the soil that supports the tree.

2. Trunk: The trunk is the primary means of support for the tree, and it consists of several layers of tissue which serve specific purposes. Here we describe each layer, beginning from the outer layer and moving inward:

-Outer Bark: The outer bark is the visible part of the trunk, and it helps protect the interior of the tree from dehydration, adverse weather, insects and diseases. As living matter within a tree grows, its outer bark becomes tauter and begins to split, contributing to the outer bark’s cracked appearance.

-Phloem: Just inside the outer bark is a layer of inner bark called phloem. Throughout its short life, phloem tissue transports food and sugars from the leaves where they are produced to the rest of the tree. When phloem dies, it turns to cork and becomes a part of the defensive outer bark layer.

-Cambium: Just inside the phloem layer lays the thinnest layer of the tree, a watery layer called the cambium. Cambium cells constantly divide during growing season and are responsible for the growth in diameter of the trunk, roots and branches.

-Xylem: The xylem, or sapwood, is a layer situated just inside the cambium layer. This layer, which is comprised of the youngest wood in the tree, transports water and nutrients from the roots to the leaves and other parts of the tree. As new cells form and the tree grows, interior xylem cells die and become a part of the tree’s heartwood, discussed next.

-Heartwood: The central, supporting core of the tree is heartwood. Heartwood is comprised of dead tissue that no longer transports water, but serves the important purpose of supporting the tree. Although heartwood can be considered dead, it will not become weaker or decay as long as the protective outer layers of the tree remain undamaged.

3. Roots: Trees often have extensive root systems, which take in water and minerals from the soil that are necessary for the tree’s survival. Roots also store sugars, anchor the tree and help control erosion of the soil below. Tree roots are usually relatively shallow where oxygen is abundant in the soil, but the roots of mature trees can span laterally to distances measuring two to three times the size of the crown. Though fairly shallow roots are common for trees, some trees also have tap roots that reach deeper into the ground.

About the Author: Andrew Johnson is the owner of Central Texas Tree Care, a leading Austin tree service provider in Central Texas (Travis County and surrounding areas). Central Texas Tree Care offers services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management and fertilization. For more information please visit http://www.centraltexastreecare.com.