Aside from the regular pruning to develop the tree into its best form to enable it to do its best work, there are wounds and malformations to be treated. Recently, the treating of injured and decayed trees has received much attention, and "tree doctors" and "tree surgeons" have engaged in the business. If there are quacks among these people, there are also competent and reliable men who are doing useful service in saving and prolonging the life of trees; one should choose a tree doctor with the same care that he would choose any other doctor. The liability of injury to street trees in the modern city and the increasing regard for trees, render the services of good experts increasingly necessary.
Street trees are injured by many causes: as, starving because of poor soil and lack of water under pavements; smoke and dust; leakage from gas mains and from electric installation; gnawing by horses; butchering by persons stringing wires; carelessness of contractors and builders; wind and ice storms; overcrowding; and the blundering work of persons who think that they know how to prune. Well-enforced municipal regulations should be able to control most of these troubles.
Along roadsides and other exposed places it is often necessary to protect newly set trees from horses, boys, and vehicles. There are various kinds of tree guards for this purpose. The best types are those that are more or less open, so as to allow the free passage of air and which are so far removed from the body of the tree that its trunk may expand without difficulty. If the guards are very tight, they may shade the trunk so much that the tree may suffer when the guard is removed, and they prevent the discovery of insects and injuries. It is important that the guard does not fill with litter in which insects may harbor. As soon as the tree is old enough to escape injury, the guards should be removed. A very good guard, made of laths held together with three strips of band-iron, and secured to iron posts, is shown in Fig. 156. Figure 157. shows a guard made by winding fencing wire upon three posts or stakes. When there is likely to be danger from too great shading of the trunk, this latter form of guard is one of the best. There are good forms of tree guards on the market. Of course hitching-posts should be provided, wherever horses are to stand, to remove the temptation of hitching to trees. Figure 158, however, shows a very good device when a hitching post is not wanted. A strong stick, four or five feet long, is secured to the tree by a staple and at the lower end of the stick is a short chain with a snap in the end. The snap is secured to the bridle, and the horse is not able to reach the tree.
Mice and rabbits.
Trees and bushes are often seriously injured by the gnawing of mice and rabbits. The best preventive is not to have the vermin. If there are no places in which rabbits and mice can burrow and breed, there will be little difficulty. At the approach of winter, if mice are feared, the dry litter should be removed from about the trees, or it should be packed down very firm, so that the mice cannot nest in it. If the rodents are very abundant, it may be advisable to wrap fine wire netting about the base of the tree. A boy who is fond of trapping or hunting will ordinarily solve the rabbit difficulty. Rags tied on sticks which are placed at intervals about the plantation will often frighten rabbits away.
Trees that are girdled by mice should be wrapped up as soon as discovered, so that the wood shall not become too dry. When warm weather approaches, shave off the edges of the girdle so that the healing tissue may grow freely, smear the whole surface with grafting-wax, or with clay, and bind the whole wound with strong cloths. Even though the tree is completely girdled for a distance of three or four inches, it usually may be saved by this treatment, unless the injury extends into the wood. The water from the roots rises through the soft wood and not between the bark and the wood, as commonly supposed. When this sap water has reached the foliage, it takes part in the elaboration of plant-food, and this food is distributed throughout the plant, the path of transfer being in the inner layers of bark. This food material, being distributed back to the girdle, will generally heal over the wound if the wood is not allowed to become dry.
In some cases, however, it is necessary to join the bark above and below the girdle by means of cions, which are whittled to a wedge-shape on either end, and inserted underneath the two edges of the bark (Fig. 159). The ends of the cions and the edges of the wound are held by a bandage of cloth, and the whole work is protected by melted grafting-wax poured upon it. [Footnote: A good grafting-wax is made as follows: Into a kettle place one part by weight of tallow, two parts of beeswax, four parts of rosin. When completely melted, pour into a tub or pail of cold water, then work it with the hands (which should be greased) until it develops a grain and becomes the color of taffy candy. The whole question of the propagation of plants is discussed in "The Nursery-Book."]
Repairing street trees.
The following advice on "tree surgery" is by A.D. Taylor (Bulletin 256, Cornell University, from which the accompanying illustrations are adapted):--
"Tree surgery includes the intelligent protection of all mechanical injuries and cavities. Pruning requires a previous intimate knowledge of the habits of growth of trees; surgery, on the other hand, requires in addition a knowledge of the best methods for making cavities air-tight and preventing decay. The filling of cavities in trees has not been practiced sufficiently long to warrant making a definite statement as to the permanent success or failure of the operation; the work is still in an experimental stage. The caring for cavities in trees must be urged as the only means of preserving affected specimens, and the preservation of many noble specimens has been at least temporarily assured through the efforts of those practicing this kind of work.
"Successful operation depends on two important factors: first, that all decayed parts of the cavity be wholly removed and the exposed surface thoroughly washed with an antiseptic; second, that the cavity, when filled, must be air tight and hermetically sealed if possible. Trees are treated as follows: The cavity is thoroughly cleaned by removing all decayed wood and washing the interior surface with a solution of copper sulfate and lime, in order to destroy any fungi that may remain. The edges of the cavity are cut smooth in order to allow free growth of the cambium after the cavity is filled. Any antiseptic, such as corrosive sublimate, creosote, or even paint, may answer the purpose; creosote, however, possesses the most penetrating powers of any. The method of filling the cavities depends to a great extent on their size and form. Very large cavities with great openings are generally bricked on the outside, over the opening, and filled on the inside with concrete, the brick serving the purpose of a retaining wall to hold the concrete in place. Concrete used for the main filling is usually made in the proportion of one part good Portland cement, two parts sand, and four parts crushed stone, the consistency of the mixture being such that it may be poured into the cavity and require little or no tamping to make the mass solid. (Fig. 160.)
[Illustration: Fig. 161. A wound, made by freezing, trimmed out and filled with cement.]
"Fillings thus made are considered by expert tree surgeons to be a permanent preventive of decay. The outside of the filling is always coated with a thin covering of concrete, consisting of one part cement to two parts fine sand. Cavities resulting from freezing, and which, though large on the inside, show only a long narrow crack on the outside, are most easily filled by placing a form against the entire length of the opening, having a space at the top through which the cement may be poured (Fig. 161). Another method of retaining the concrete is to reinforce it from the outside by driving rows of spikes along the inner surface of either side of the cavity and lacing a stout wire across the face of the cavity. For best results, all fillings must come flush with the inner bark when finished. During the first year, this growing tissue will spread over the outer edge of the filling, thus forming an hermetically sealed cavity. In the course of time, the outside of small or narrow openings should be completely covered with tissue, which buries the filling from view.
[Illustration: Fig. 162. Bridge-grafting or in-arching from saplings planted about the tree.]
"It has been found that there is a tendency for portland cement to contract from the wood after it dries, leaving a space between the wood and the cement through which water and germs of decay may enter. A remedy for this defect has been suggested in the use of a thick coat of tar, or an elastic cement which might be spread over the surface of the cavity before filling. The cracking of portland cement on the surface of long cavities is caused by the swaying of trees during heavy storms, and should not occur if the filling is correctly done.
"In addition to the preservation of decayed specimens by filling the cavities, as above outlined, it has been proposed to strengthen the tree by treating it as shown in Fig. 162. Young saplings of the same species, after having become established as shown, are grafted by approach to the mature specimen.
[Illustration: Fig. 163. Faulty methods of bracing a crotched tree. The lower method is wholly wrong. The upper method is good if the bolt-heads are properly counter-sunk and the bolts tightly fitted; but if the distance between the branches is great, it is better to have two bolts and join them by hooks, to allow of wind movements.]
"Injury frequently results from error in the method of attempting to save broken, or to strengthen and support weak branches that are otherwise healthy. The means used for supporting cracked, wind-racked, and overladen branches which show a tendency to split at the forks are bolting and chaining. The practice of placing iron bands around large branches in order to protect them has resulted in much harm; as the tree grows and expands, such bands tighten, causing the bark to be broken and resulting after a few years in a partial girdling (Fig. 163).
[Illustration: Fig. 164. Trees ruined to allow of the passage of wires.]
"To bolt a tree correctly is comparatively inexpensive. The safest method consists in passing a strong bolt through a hole bored in the branch for this purpose, and fastening it on the outside by means of a washer and a nut. Generally the washer has been placed against the bark and the nut then holds it in place. A better method of bolting, and one which insures a neat appearance of the branch in addition to serving as the most certain safeguard against the entrance of disease, is to counter-sink the nut in the bark and imbed it in portland cement. The hole for the sinking of the nut and washer is thickly coated with lead paint and then with a layer of cement, on which are placed the nut and washer, both of which are then imbedded in cement. If the outer surface of the nut be flush with the plane of the bark, within a few years it will be covered by the growing tissue.
[Illustration: Fig. 168. The proper way to saw off a large limb. A cut is first made on the under side to prevent splitting down; then it is cut on the upper side. Then the entire "stub" is removed close to the trunk.]
[Illustration: Fig. 169. A weak-bodied young tree well supported; padding is placed under the bandages.]
[Illustration: Fig. 172. The best way of attaching a guy rope, if a tree must be used as support.]
"The inner ends of the rods in the two branches may be connected by a rod or chain. The preference for the chain over the rod attachment is based on the compressive and tensile stresses which come on the connection during wind storms. Rod connections are preferred, however, when rigidity is required, as in unions made close to the crotch; but for tying two branches together before they have shown signs of weakening at the fork, the chain may best be used, as the point of attachment may be placed some distance from the crotch, where the flexibility factor will be important and the strain comparatively small. Elms in an advanced stage of maturity, if subjected to severe climatic conditions, often show this tendency to split. These trees, especially, should be carefully inspected and means taken to preserve them, by bolting if necessary."
[Illustration: IX. A rocky bank covered with permanent informal planting.]
[Illustration: Fig. 173. A method of saving valuable trees along streets on which heavy lowering of grade has been made.]
The illustrations, Figs. 164-173, are self-explanatory, and show poor practice and good practice in the care of trees.