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.