18 Sep2000

Overstory #68 - Twelve Tree Myths

Written by Alex L. Shigo.

Editor's Note

In this edition of The Overstory special guest author Dr. Alex L. Shigo, retired chief scientist of the U.S. Forest Service and author of numerous books including _Modern Arboriculture_, clarifies twelve common misconceptions about trees. As Dr. Shigo says, "If we can understand more completely how trees function, then our work will be more enjoyable and profitable and our efforts to maintain healthy trees will be more effective."

Twelve Tree Myths

"Myth" is used here to include misconceptions, misunderstandings, and, mostly, half-truths.

Many of the corrections to the myths listed here are known by many people. I believe the myths persist because many of the myths taken alone appear trivial or a matter of semantics. However, each myth is like a thread. When a hundred or more weak threads are used to make a fabric called a profession, the profession will only be as strong as the threads that form it.

Natural systems have more variables than any other system on earth. The responsibility of tree care professionals is to manage a large part of that system in ways that will benefit all members of the system. Not an easy task! Because there are so many parts of the natural systems that are beyond our regulation, we need every bit of clarity, exactness, and sound understanding of those parts we can regulate. Then, and only then, will we be able to manage tree systems, and environmental systems, in ways that ensure high quality survival for all the connected members.

Myth 1: "Forests are groups of trees."

Forests are highly ordered connections of many living communities with trees. The connections ensure survival of the trees and their associates.

Myth 2: "Nature is balanced."

Balanced means the equalization of opposing forces. Natural systems survive because they are in continuing states of dynamic equilibrium. They vibrate. They adjust to a continuing feedback process for survival. Natural systems are not balanced in the sense of no motion or no change. They are not static.

Myth 3: "Wood is dead."

In living trees there are more living cells in sapwood than dead cells. There are no living cells in heartwood, wetwood, discolored wood, and false heartwood. Wood is a highly ordered arrangement of living, dying, and dead cells. The cell walls are made up of cellulose, lignin, and hemicelluloses. Vessels and tracheids are very large compared to axial and radical parenchyma cells. Vessels, fibers, and tracheids live only a short time. Therefore, on a volume basis, sapwood is mostly dead, and on a number-of-cell basis, sapwood is mostly alive.

Myth 4: "Photosynthesis is most active during bright, hot days over 100 deg F (38 C deg)."

Photosynthesis decreases rapidly as temperatures begin to exceed 100 deg F (38 C deg). For photosynthesis to occur, guard cells must be open to receive carbon dioxide. When guard cells are open, moisture leaves the plant.

Myth 5: "Water causes rot."

Microorganisms cause rot. Moisture at very precise amounts is a requirement for decay. Too much or too little moisture does not support decay. The high moisture content of wood in living trees is a protection feature against the spread of decay.

Myth 6: "Roots are the most important part of a tree."

Roots and the trunk with a crown of leaves are equally important; dynamic equilibrium. The roots (woody, nonwoody) and the crown (branches, leaves) act as a seesaw in motion. The seesaw functions only so long as it is going upward and downward. So it is with roots and crown. Each is dependent on the other, and the tree system survives because there is a continuing dynamic equilibrium between roots and crown. To say one portion is more important than the other indicates a complete lack of understanding of the way the tree system functions.

Myth 7: "Ants speed up the decay process."

Ants keep their galleries very clean and in so doing they slow the decay process. Ants live in the tree and eat elsewhere. Termites "eat" in the tree and live elsewhere. (Some tropical termites live in nests on tree branches, but they still live outside the tree.)

Myth 8: "All insects and fungi that live on, in, and about trees are harmful."

It is difficult to have an exact percentage, but roughly less then one percent of the insects and fungi and live on, in, and about trees are harmful. Insects are highly beneficial for pollination. Thousands of fungus species are beneficial as symbiotes in mycorrhizae. Bacteria and actinomycetes form nodules that fix nitrogen. Decay fungi rot the base of dead branches and aid in shedding. The list goes on and on. The major point here is to make certain that we do not kill the ninety-nine percent while pursuing the one percent.

Myth 9: "A healthy tree is a tree free of infections."

A tree can be very healthy and still have thousands of infections. The infections will be walled off or compartmentalized. Isolations for microorganisms from the compartmentalized tissues usually yield bacteria and fungi. Health means the ability to resist strain. Strain means the irreversible point beyond stress. Stress means that reversible point where a system begins to operate near the limits for which it was designed.

Myth 10: "All wood-product problems start after the tree is cut."

Most wood-product problems start in the living tree. The problem here is that most studies on wood-product problems have started with the products, not with the living trees. The patterns of decay in products usually follow the patterns set in the living tree. But, if the living tree patterns are not understood first, then the products problems cannot be related to the tree. For example, wood altered only slightly in the living tree will be the wood first to absorb moisture in the product.

Myth 11: "Fertilizer is tree food."

This is a half truth were the wrong half has become the accepted part. Fertilizers provide elements that are essential for growth. Fertilizers do NOT provide an energy source for trees and other plants.

A food is any substance that provides the essentials for life; an adequate source of elements that are essential, but do not provide energy, and other types of elements that do provide energy (carbohydrates). Unlike animals, trees are able to trap the energy of the sun in a molecule called glucose. THIS is the essential energy source for the tree.

From the soil, trees obtain water and other elements that are essential for life. These do not provide an energy source for the tree.

Yes, soil elements in many chemical combinations can and do provide energy for bacteria and bacteria-like organisms. But trees do not work that way. Correct fertilization should consider the tree and its age and condition, the soil type and pH, the elements lacking in the soil, and the desires of the tree owner. The variables are almost endless.

The entire subject of fertilizers needs a thorough "clean up." Many people do not understand the numbers given to N, P, and K on bags of "plant food!" It is beyond the scope of this publication to try to clarify the subject here. (For more information, see Modern Aboriculture p.232-245.)

Myth 12: "Anybody can plant a tree correctly!"

The rush is on to plant trees. Kings, queens, presidents, governors, and many organizations worldwide are telling people to plant trees. The implication is that everybody knows how to plant a tree correctly. However, incorrect planting procedures, and planting the wrong tree in the wrong place, have caused a multitude of tree problems worldwide.

Yes, trees should be planted. They should be planted correctly.

If correct planting procedures are not known, then trees should be planted under the supervision of someone who understands how to plant correctly, and who also understands the concept of the right tree in the right place. And, after planting, a continuing health care schedule should be maintained.

The next edition of The Overstory (#69) will include Dr. Shigo's summary comments on correct planting procedures for trees.

Reference

Shigo, A.L. 1991. Modern Arboriculture: a systems approach to the care of trees and their associates. Shigo and Trees, Associates. Durham, New Hampshire 03824-3105, USA.

About the Author

Dr. Alex L. Shigo is considered by many to be one of the foremost authorities on trees in the world today. Retired from the U.S. Forest Service, he is an internationally recognized researcher credited with the development of expanded interpretations of decay based on compartmentalization and microbial succession. His research includes over 15,000 longitudinal tree dissections with a chain saw. He has published over 15 textbooks used in many universities worldwide. For more information about seminars and to order Dr. Shigo's publications, contact: SHIGO AND TREES, ASSOCIATES, P.O. Box 769, Durham, NH 03824, USA. Phone: 603-868-7459; Fax: 603-868-1045.

Original Source

This excerpt is adapted from _100 Tree Myths_ with the kind permission of the author. The full text, including numerous photographs and figures can be purchased from Shigo and Trees, Associates, P.O. Box 769, Durham, NH 03824, USA. Phone: 603-868-7459; Fax: 603-868-1045.