The Makings of a Tree

Most learn about trees in grade school, but how many remember its anatomy and the fascinating complexity of what contributes to a tree's health. For those of you who can't remember, here they are:

Branches - Most know what a branch is, but did you know they are attached to the tree by interlocking branch and trunk tissue? Each year, a new layer of interlocking tissue is produced covering the previous year's layers. A woody branch collar, produced by the trunk, holds the branch base. A branch will grow in diameter until it runs out of room. Leaves on every branch must produce enough food to feed itself. Food does not move from roots or other branches to supply a starving branch. Branches unable to support themselves are sealed off. Branches on the interior of a shade tree that do not receive adequate light will die and eventually fall.

Roots - A tree's roots are important and to keep the tree healthy roots need an adequate amount of oxygen and moisture. Most active tree roots are in the top 3 feet of soil; the majority is in the top 12 inches. The more compacted or poorly drained the soil the closer the roots are to the soil surface. A tree's roots will grow most of the year, stopping only when soil temperatures are cold. A tree has perennial woody roots and annual absorbing roots. Woody roots become thicker each year. The absorbing roots die but are replaced by new absorbing roots. Annual absorbing roots form shallow, horizontal fans that take-up water and nutrients. A few woody support roots grow downward and outward to anchor the tree in place. Most trees do not have a deep taproot. While a taproot may develop on trees growing in the woods in well-drained soils, they generally do not develop on trees transplanted into the landscape or on trees grown in compacted or poorly drained soil.

Roots can grow outward to about three times the width of the branch spread but only 50 percent of the root system occurs between the trunk and the dripline. The foliage of a tree is supplied by the roots on the same side. If a tree begins to wither on one side, it can often be due to the roots on that same side being injured. With some trees, such as maple, the effect may develop anywhere in the tree canopy.

Tree roots tend to avoid each other when young, but as they grow they may be forced together and from a graft union. These grafts can conduct diseases from one tree to another.


Leaves - Leaves are the food factories of the tree. Sunlight creates chlorophyll within the leaves. This along with carbon dioxide and water produce life-sustaining carbohydrates through a process called photosynthesis. Leaves are also responsible for respiration and transpiration. The lobes, leaflets and jagged edges of many broad leaves have their uses, too. They help evaporate the water used in food-building, reduce wind resistance and even provide "drip tips" to shed rain that, left standing, could decay the leaf. Besides its branches, roots, and leaves, a mature tree grows another important structure - the flower (or cone, in the case of evergreens). These are the reproductive structures from which the seeds are produced.

While a tree's components may seem basic, its anatomy is actually quite complex and an amazing illustration of nature at its best.

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

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.