Trees

1. Q. What is the most reasonably priced horticultural gift which I can give for Christmas which will eventually appreciate in value over the years?

A. If you want a carefree gift which will greatly appreciate in value over the years, a well-adapted tree is hard to beat. Trees can be purchased and planted for approximately $100 per inch diameter of trunk. Within 45 years the same tree will have generated an accumulated worth of $196,250.

A tree living for 50 years will generate $31,250 worth of oxygen, provide $62,000 worth of air pollution control, control soil erosion and increase soil fertility to the tune of $31,250, recycle $37,500 worth of water, and provide a home for animals worth $31,250. This figure does not include the value of the fruits, lumber, or beauty derived from trees. There is no another Christmas gift in the tree price range which can make the same claim! Be sure to choose well-adapted species such as Chinese Pistache, Texas Red Oak, Hybrid Crape Myrtle, Montezuma Cypress or Afgan Pine.

2. Q. I have been told that trees can be eventually killed if trunks are damaged by flexible string trimmers. How does this happen, and how long can a tree live?

A. A weakening and eventual death of a tree occurs if a strip of bark is removed or damaged completely around the trunk by the beating action when trimming occurs.

Sugars produced in the leaves are translocated downward to the roots in the inner bark (phloem). The root cells add mineral elements absorbed from the soil solution to these sugars to produce other compounds required for growth and development. When the supply of sugar is interrupted by girdling, the available sugar and stored carbohydrates are gradually depleted and the roots die.

The tree may die the same year it is girdled, but there are many reported cases of girdled trees continuing to grow for two years and then failing to leaf out the third year.

3. Q. Several of my neighbors have had the trees in their yard topped. The trees look awful! What do you think about this practice?

A. Topping trees is not pruning, it's butchery - - "tree slaughter," if you please. In addition to ruining the natural shape and beauty of large shade trees, topping invites problems - - real problems. Severe pruning, like an illness, weakens the plant and lowers its resistance to insects and diseases. These pests can easily enter through open pruning wounds. So what's the answer? Three ideas come to mind:

4. Q. Is there any new information from the experts concerning tree care?

A. Here are some treatments that can help trees stay healthy:

  1. Plant the right tree in the right place. Do not plant trees that will grow to be tall and massive in small spaces or under power lines. If this is done, then there will not be a need to top trees. Tree topping is a serious injury no matter how the treatment is made. Young trees may be topped to regulate size and shape. Rather than topping a mature tree, maybe a new tree is needed.
  2. Start pruning programs early in the life of the tree and keep it up. Do not make cuts that remove the branch flush with the trunk. Flush cuts start at least 14 serious injuries.
  3. Fertilizers provide elements that may be required for healthy growth. Fertilizers do not provide energy releasing substances. Fertilizers are not tree food. Tree food comes from the leaves. Keep leaves healthy so that the tree can get its food. Too much fertilizer can cause problems. Most planted trees can benefit from proper fertilization.
  4. Roots of most trees seldom grow deeper than 40 inches. The roots usually grow beyond the tree crown dripline. The nonwoody roots are associated with beneficial fungi to form mycorrhizae (soil organisms). Construction injury may harm a tree directly by wounding the woody support roots and indirectly by harming the mycorrhizae. If possible, cut injured woody roots to make a smooth, clean surface free of torn tissues. Do not fertilize the soil where there are large wounded woody roots. The fertilizer will benefit the fungi as they grow into the roots. Be on guard where new lawns are planted over injured woody roots and the lawn is watered and fertilized. A very serious hazard condition could result as the tree crown grows larger and as the woody roots rot faster.
  5. Make tree protection plans BEFORE construction starts. Make sure the developer understands that it is important!

Let us try to understand and appreciate the complexity of a tree.

Trees are huge - - larger than the biggest whale. Individual leaves and roots are extremely small in relation to the whole tree. Very few human beings have had the privilege of actually seeing even a comprehensible fraction of the root system of an entire tree. Illustrations in textbooks, natural history books, and in manuals of landscape architecture and tree care are usually creations of artistic imagination and are usually terribly wrong. It is impossible to accurately portray or represent an entire tree with its roots on the page of a typical textbook. The problems of scale are overwhelming. A healthy, open-grown oak tree, 40 years old, has a trunk 70 feet tall and 2 feet in diameter. The spread of the branches of an open grown tree is rarely less than two-thirds of the height of the tree and is often equal to or greater than the height. The leaf bearing surface of the tree extends to within l0 to 20 feet of the ground, and a typical branch forks four to five times from its origin to the smallest twigs. As described previously, root spread of a typical, open-grown tree is usually greater than 30 feet beyond the tips of the branches and can commonly extend in a circle with a diameter two or more times the height of the tree. Illustration of a tree in proper scale with a textbook held in its upright position would require a 317:1 reduction in the dimensions of all parts.

Only a small part of a living tree is actually alive. The very tips of the roots. The leaves. The buds. The flowers. The seeds. And a single thin layer of cells that sheathes the entire tree from the tips of the roots to the buds on the ends of the smallest branches.

But those living parts of the tree - - about one percent of its bulk - - perform amazingly complex functions. And build a structure that can soar skyward a hundred feet or more and stand for centuries.

A large tree has hundreds of miles of roots to anchor it to the soil. But most of that length is dead, woody matter. At the very tips of the roots are living, growing cells that push a protective cap of dead cells through the soil. Just behind the tips are the root hairs, tiny, single-cell projections that absorb water and dissolved minerals from the soil, and start it on its way up to the leaves.

Extending from the tips of the roots to the ends of the branches is a single layer of living cells - - the cambium layer. They are the only living cells in the trunk. In summer, when the tree grows, these cells divide continually - - adding thickness but no height to the tree. The cells that form on the outside of the cambium layer become bark; those that form on the inside become wood.

The leaves - - or needles, in coniferous trees - - make sugar out of water passed up from the roots and carbon dioxide in the air. In doing this they utilize the energy of light, with the aid of chlorophyll. The sugar is passed back to the other living cells of the tree so that they can breathe - - that is, combine the sugar with oxygen to create energy for the infinite processes of life which enable them to grow and develop.

The leaf buds on the twigs are alive, too. It is their growth that gives a tree height, and extends its branches. Cells at the base of the bud divide and elongate, building a new twig behind the developing leaf. This growth is coordinated with the growth in the cambium layer, so that as a tree grows in height, its trunk and its branches are all growing in thickness at the same time.

Growth of a plant is an integrated phenomenon that depends on a proper balance and functioning of all plant parts. If a large portion of the roots is killed, a corresponding portion of the leaves and branches will die. If a tree is defoliated repeatedly, some of its roots will die. The finest roots of a tree are connected to the leaves by an elaborate plumbing system of larger transport roots, trunk, branches, and twigs. Five percent is fine or feeder roots, 15 percent is larger or transport roots, 60 percent is trunk or main stem, 15 percent is branches and twigs, and 5 percent is leaves. The quantity of roots decreases rapidly with increasing depth in normal soils, so that 99 percent of the roots are usually included in the surface meter of soil. In oaks, a given root is directly connected to a particular set of branches usually on the same side of the tree as the root. Death or damage to the roots of trees with such restricted, one-sided plumbing systems usually results in death of the corresponding branches.

In typical clay-loam soils, these roots are usually located less than 8 to 12 inches below the surface and grow outward far beyond the branch tips of the tree. The system of framework roots, often called "transport" roots, extends frequently to encompass a roughly circular area four to seven times the area delineated by an imaginary downward projection of the branch tips. It is not uncommon to find trees with root systems having an area with a diameter one, two, or more times the height of the tree. A complex system of smaller roots grows outward and predominantly upward from the system of framework roots. These smaller roots branch four or more times to form fans or mats of thousands of fine, short, non-woody tips. Many of these smaller roots and their multiple tips are 0.2 to 1 mm or less in diameter and less than 1 to 2 mm long. These fine, non-woody roots constitute the major fraction of the surface of the root system of a tree. Their multiple tips are the primary sites of absorption of water and minerals. Hence, they are often called "feeder roots." The delicate, non-woody root system is killed frequently by these fluctuations in the soil environment. Nematodes, springtails, and other members of the soil micro-fauna are constantly nibbling away at these succulent, non-woody tree roots. Injury to and death of roots is frequent, and is caused by many agents. New roots form rapidly after injuries, so the population and concentration of roots in the soil is as, or more dynamic than, the population of leaves in the air above. In brief, large, woody tree roots grow horizontally through the soil and are perennial. They are predominantly located in the top 12 inches of soil and do not normally extend to depths greater than 3 to 7 feet. They often extend outward from the trunk of the tree to occupy an irregularly shaped area four to seven times larger than the projected crown area and having an average diameter equivalent to one, two, or more times the height of the tree.

Roots grow where the resources of life are available. They do not grow to or toward anything. They cannot grow where there is no oxygen or where the soil is compacted and hard to penetrate. There is no such thing as a "shallow rooted" or a "deep rooted" species of tree. Cypress and willow trees will grow down deeply into the soil, down cracks, and down sewer lines if oxygen and water supplies are adequate. The roots of pines, hickories and other upland species will follow along the surface if the soil is too compact and hard or if oxygen supplies are limited to the surface. Roots grow parallel to the surface of the soil so that trees on slopes have sloping root systems. Roots often grow along cracks, crevices, and through air spaces for unbelievable distances under the most impermeable pavements and impenetrable soils. Roots commonly grow down cracks between fracture columns ("peds") in heavy clay soils that they could not otherwise penetrate.

A significant portion of the root system of all trees in all soils is concentrated in the top few millimeters of soil. Indeed, tree roots grow right into the litter layer of the forest, in among the grass roots of a city lawn, and in the crevices of the bricks, concrete, and asphalt of city pavements. Fertilizer broadcast on the surface of the soil is immediately available to tree roots. It does not have to move down into the soil. Even the reportedly immobile phosphates are immediately available to tree roots. That is why researchers were unable to show any differences in the response of trees to fertilizer placed in holes or broadcast on the surface. Foresters broadcast fertilizers on millions of acres of land and achieve rapid and large returns on their investments. Except for where slow release fertilizers are used for special effects, there is no justification for "tree spikes" or other formulations of fertilizer in holes bored in the ground or for injecting fertilizer into the soil. Herbicides and other chemicals should be used only with extreme care near trees and shrubs. Again, many tree roots are in and near the surface of the soil and extend far beyond the tips of the branches of the tree tips. Trees are really "broad leaves weeds" when they grow in a lawn and application of weed killers alone or in combination with other herbicides or in combination with fertilizers will injure trees. Roots grow in cracks and crevices of pavement. Applications of sterilants and herbicides to kill weeds in these situations can kill trees 60 feet or more away from where they are applied. Larger residential lots are 105 feet by 150 feet. The roots of a large tree will commonly occupy the entire front or backyard and trespass into the neighboring property. No part of an urban yard can be treated carelessly with herbicides. The largest single killer of trees is soil compaction - - compaction from excessive use of city parks by people and pigeons whose small feet exert greater pressure than heavy machines. Trees are also killed by compaction from construction equipment, compaction from livestock including zoo animals, and compaction in unpaved parking areas. compaction closes the pore spaces which are essential to the absorption of water and oxygen; hardens all but the sandiest of soils so that roots cannot penetrate them - - even when oxygen supplies are adequate. It should be obvious that any grading or other activity that buries or cuts off tree roots will result in the death of a corresponding portion of the branches in the tree. Yet this simple fact is ignored when utility lines, parking lots, and even irrigation lines are being installed. Smearing six inches of clay over the root system of an established tree is usually as lethal as covering its roots with pavement or cutting it down with a chain saw. Even a one quarter inch soil covering can cause root mortality. A residential yard in a new development may have six different ditch-witch lines cut from the street to the house; for water, for sewer, for electricity, for telephone, for gas, and for cable television. Over 90 percent of the roots in the front yard are destroyed in construction and utility line installation, and the soil structure in the entire yard is usually completely destroyed by compaction and the spreading of excavated heavy soil on top of undisturbed soil. The proud new homeowners wonder why all of their trees have severe crown die back and continue to decline and die for a decade or more after they move in. It is because the builders and all the utility people cut off 90 percent of the roots, mistreated the soil, and because the new owners tore up the rest of the roots to plant a lawn and garden. Tunneling and concentrating utility line installations and other techniques can minimize this damage. Careful watering and thinning of the tree crowns to compensate for root losses can allow the residual roots time to supply extra water and nutrients while new roots grow and become established. There are other techniques that require a general knowledge of physiology that are beyond the topics covered in this chapter. It is often wise and cheapest to accept the situation and cut down the tree and plant a new one. Tree surgery and tree removal, after construction is complete and crown die back is obvious, can cost hundreds of dollars per year and require annual investments for ten or more years after construction. Surprisingly, soil compaction and limited oxygen supplies are the major restraints to growing trees in city parks and highly paved areas. Inadequate supplies of water are usually secondary to these fundamental problems.

Keep this information in mind as you work around established trees or plant new trees. Remember the life you save may not be your own - - it may be your tree's!


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