Fundamental principles: Trees are very much like human beings in their requirements, mode of life and diseases, and the general principles applicable to the care of one are equally important to the intelligent treatment of the other. The removal of limbs from trees, as well as from human beings, must be done sparingly and judiciously. Wounds, in both trees and human beings, must be disinfected and dressed to keep out all fungus or disease germs. Fungous growths of trees are similar to human cancers, both in the manner of their development and the surgical treatment which they require. Improper pruning will invite fungi and insects to the tree, hence the importance of a knowledge of fundamental principles in this branch of tree care.
Tree Disease
Time: Too much pruning at one time should never be practiced, and no branch should be removed from a tree without good reason for so doing. Dead and broken branches should be removed as soon as observed, regardless of any special pruning season, because they are dangerous, unsightly and carry insects and disease into the heart of the tree. But all other pruning, whether it be for the purpose of perfecting the form in shade trees, or for increasing the production of fruit in orchard trees, should be confined to certain seasons. Shade and ornamental trees can best be pruned in the fall, while the leaves are still on the tree and while the tree itself is in practically a dormant state.
Tree Pruning
Proper cutting: All pruning should be commenced at the top of the tree and finished at the bottom. A shortened branch (excepting in poplars and willows, which should be cut in closely) should terminate in small twigs which may draw the sap to the freshly cut wound; where a branch is removed entirely, the cut should be made-close and even with the trunk. Wherever there is a stub left after cutting off a branch, the growing tissue of the tree cannot cover it and the stub eventually decays, falls out and leaves a hole, which serves to carry disease and insects to the heart of the tree. This idea of close cutting cannot be over-emphasized.
Tree Pruning
Where large branches have to be removed, the splitting and ripping of the bark along the trunk is prevented by making one cut beneath the branch, about a foot or two away from the trunk, and then another above, close to the trunk.

Too severe pruning: In pruning trees, many people have a tendency to cut them back so severely as to remove everything but the bare trunk and a few of the main branches. This process is known as "heading back." It is a method, however, which should not be resorted to except in trees that are very old and failing, and even there only with certain species, like the silver maple, sycamore, linden and elm. Trees like the sugar maple will not stand this treatment at all. The willow is a tree that will stand the process very readily and the Carolina poplar must be cut back every few years, in order to keep its crown from becoming too tall, scraggy and unsafe.
Excess Pruning
Covering woods: The importance of immediately covering all wounds with coal tar cannot be overstated. If the wound is not tarred, the exposed wood cracks, providing suitable quarters for disease germs that will eventually destroy the body of the tree. Coal tar is by far preferable to paint and other substances for covering the wound. The tar penetrates the exposed wood, producing an antiseptic as well as a protective effect. Paint only forms a covering, which may peel off in course of time and which will later protrude from the cut, thus forming, between the paint and the wood, a suitable breeding place for the development of destructive fungi or disease. The application of tin covers, burlap, or other bandages to the wound is equally futile, and in most cases, even injurious.

Tools used in pruning: Good tools are essential for quick and effective work in pruning. Two or three good saws, a pair of pole-shears, a pole-saw, a 16-foot single ladder, a 40-foot extension ladder of light spruce or pine with hickory rungs, a good pruning knife, plenty of coal tar, a fire-can to heat the tar, a pole-brush, a small hand brush and plenty of good rope comprise the principal equipment of the pruner.
Vintage Tools


Where trees have been properly cared for from their early start, wounds and cavities and their subsequent elaborate treatment have no place. But where trees have been neglected or improperly cared for, wounds and cavities are bound to occur and early treatment becomes a necessity.

There are two kinds of wounds on trees: (1) surface wounds, which do not extend beyond the inner bark, and (2) deep wounds or cavities, which may range from a small hole in a crotch to the hollow of an entire trunk.
Cut Branch Wound
Surface wounds: Surface wounds are due to bruised bark, and a tree thus injured can no longer produce the proper amount of foliage or remain healthy very long. The reason for this becomes very apparent when one looks into the nature of the living or active tissue of a tree and notes how this tissue becomes affected by such injuries.

This living or active tissue is known as the "cambium layer," and is a thin tissue situated immediately under the bark. It must completely envelop the stem, root and branches of the trees. The outer bark is a protective covering to this living layer, while the entire interior wood tissue chiefly serves as a skeleton or support for the tree. The cambium layer is the real, active part of the tree. It is the part which transmits the sap from the base of the tree to its crown; it is the part which causes the tree to grow by the formation of new cells, piled up in the form of rings around the heart of the tree; and it is also the part which prevents the entrance of insects and disease to the inner wood. From this it is quite evident that any injury to the bark, and consequently to this cambium layer alongside of it, will not only cut off a portion of the sap supply and hinder the growth of the tree to an extent proportional to the size of the wound, but will also expose the inner wood to the action of decay. The wound may, at first, appear insignificant, but, if neglected, it will soon commence to decay and thus to carry disease and insects into the tree. The tree then becomes hollow and dangerous and its life is doomed.
Resin Discharge
Injury to the cambium layer, resulting in surface wounds, may be due to the improper cutting of a branch, to the bite of a horse, to the cut of a knife or the careless wielding of an axe, to the boring of an insect, or to the decay of a fungous disease. Whatever the cause, the remedy lies in cleaning out all decayed wood, removing the loose bark and covering the exposed wood with coal tar.
Tree Wound with Resin
In cutting off the loose bark, the edges should be made smooth before the coal tar is applied. Loose bark, put back against a tree, will never grow and will only tend to harbor insects and disease. Bandages, too, are hurtful because, underneath the bandage, disease will develop more rapidly than where the wound is exposed to the sun and wind. The application of tin or manure to wounds is often indulged in and is equally injurious to the tree. The secret of all wound treatment is to keep the wound smooth, clean to the live tissue, and well covered with coal tar.

The chisel or gouge is the best tool to employ in this work. A sharp hawk-billed knife will be useful in cutting off the loose bark. Coal tar is the best material for covering wounds because it has both an antiseptic and a protective effect on the wood tissue. Paint, which is very often used as a substitute for coal tar, is not as effective, because the paint is apt to peel in time, thus allowing moisture and disease to enter the crevice between the paint and the wood.
Chisel and Hammer
Cavities: Deep wounds and cavities are generally the result of stubs that have been permitted to rot and fall out. Surface wounds allowed to decay will deepen in course of time and produce cavities. Cavities in trees are especially susceptible to the attack of disease because, in a cavity, there is bound to exist an accumulation of moisture. With this, there is also considerable darkness and protection from wind and cold, and these are all ideal conditions for the development of disease.
Mushrooms Growing in Wound
The successful application of a remedy, in all cavity treatment, hinges on this principal condition—that all traces of disease shall be entirely eliminated before treatment is commenced.

The chisel, gouge, mall and knife are the tools, and it is better to cut deep and remove every trace of decayed wood than it is to leave a smaller hole in an unhealthy state. The inner surface of the cavity should then be covered with a coat of white lead paint, which acts as a disinfectant and helps to hold the filling. Corrosive sublimate or Bordeaux mixture may be used as a substitute for the white lead paint. A coat of coal tar over the paint is the next step. The cavity is then solidly packed with bricks, stones and mortar, and finished with a layer of cement at the mouth of the orifice.


Study the lesson for one week.

Over the week:

  • Read the lesson.
  • Review the synopsis.
  • Recite aloud the vocabulary words and their definitions.
  • Learn the concepts.
  • Complete the enrichment activities.
  • Study the review questions.


This lesson addresses proper tree pruning practices, pruning tools, and tree repair. Wounded trees must be protected from infection and diseases similar to humans. Trees can be best pruned in the autumn, although dead branches should be removed immediately. Overpruning may damage trees and should be avoided. Tools such as saws, pole-shears, ladders, pruning knives, chisels, and gouges prove useful for tree maintenance. The outer bark of the tree protects the living cambium layer, which transmits the sap from root to crown. If wounded, the cambium layer should be cleaned and covered to prevent the spread of insects and infection.


Prune: To trim a tree or shrub, often to make more healthy or productive.
Cambium: A layer of cells between the xylem and the phloem that is responsible for the secondary growth of roots and stems.
Infection: An uncontrolled growth of harmful microorganisms, such as bacteria, in a host.



Tree repair tools include saws, shears, ladders, pruning knives, chisels, and gouges. See each below.

  1. Saw: A tool with a toothed blade used for cutting hard substances, in particular wood or metal.
  2. Shears: A cutting tool similar to scissors, but often larger.
  3. Ladder: A frame, usually portable, of wood, metal, or rope, used for ascent and descent, consisting of two side pieces to which are fastened rungs.
  4. Pruning Knife: A hook shaped knife used for cutting stems and bark.
  5. Chisel: A cutting tool consisting of a slim oblong block of metal with a sharp wedge or bevel formed on one end.
  6. Gouge: A chisel with a curved blade for cutting or scooping channels, grooves, or holes in wood, stone.


Activity 1: Narrate the Lesson

  • After reading or listening to the lesson, narrate the lesson aloud using your own words.

Activity 2: Study the Lesson Pictures

  • Study the lesson pictures and describe how they relate to the lesson.

Activity 3: Take a Nature Walk

  • Bring a small sketchbook, embark upon a nature walk, and find trees with evidence of pruning and repair.
  • Make observations, make sketches, and gather data.
  • Use the gathered information to create the field book entry.

Activity 4: Complete a Field Book Entry   

After your nature walk, complete page 39 in 'Science Field Book for Fourth Grade.'


Question 1

Should you overprune a tree?
1 / 5

Answer 1

No, too much pruning can damage trees.
1 / 5

Question 2

When is the best time of year in general to prune trees?
2 / 5

Answer 2

The best time of year in general to prune trees is in the autumn.
2 / 5

Question 3

Should you wait until autumn to prune dead branches?
3 / 5

Answer 3

No, dead branches should be pruned immediately.
3 / 5

Question 4

Do trees suffer from infection and cancerous-like growths similar to humans?
4 / 5

Answer 4

Yes, trees suffer from infection and cancerous-like growths similar to humans.
4 / 5

Question 5

What do the ladder, saw, chisel, and gouge have in common?
5 / 5

Answer 5

The ladder, saw, chisel, and gouge are all tools used to maintain and repair trees.
5 / 5

  1. Should you overprune a tree? No, too much pruning can damage trees.
  2. When is the best time of year in general to prune trees? The best time of year in general to prune trees is in the autumn.
  3. Should you wait until autumn to prune dead branches? No, dead branches should be pruned immediately.
  4. Do trees suffer from infection and cancerous-like growths similar to humans? Yes, trees suffer from infection and cancerous-like growths similar to humans.
  5. What do the ladder, saw, chisel, and gouge have in common? The ladder, saw, chisel, and gouge are all tools used to maintain and repair trees.


  1. 'Studies of Trees' by Jacob Joshua Levison. n.p.