Chapter XVI Bracing and Repairing Trees
Though occasionally resorted to in olden times, particularly in the case of orchard trees, it is only of late years that the systematic treatment of tree wounds and diseases has been generally adopted. Even at the present time, the filling of hollow trunks, bracing of heavy and diseased branches and attention to insect and fungoid pests are rarely engaged in and but imperfectly understood.
When the value of old trees in an ornamental or utilitarian sense is taken into account, it is remarkable what a small amount of attention they receive when subjected to accident or disease. As a general rule, cavities or hollows in a tree stem, if left to themselves, gradually increase in size until the ascending sap is entirely cut off, when the crumbling stem either falls to pieces or is broken over by the wind. A branch requires to be braced or strengthened when from its weight and shape it is likely to get wrenched from the main stem during stormy weather and so injure the tree or man its natural beauty.
Both insect and fungoid pests do a considerable amount of damage to trees, both young and old, but as special chapters are devoted to their depredations they need only receive a passing notice here.
Hollow Trunks and their Treatment.—However desirable it may be to repair hollow trunks, yet a great deal of discrimination is necessary in deciding which trees should be operated upon, especially in the case of such as are reduced to mere shells and are not likely to derive any benefit commensurate with the labour and cost of materials involved in bracing and filling.
Young, healthy, vigorous growing trees, that have become damaged or diseased, should in the majority of instances be attended to; but in the case of old specimens on which a great amount of labour and money would necessarily have to be expended, several important bearings must be considered before works of repair are taken in hand. Historic and valuable trees, those occupying prominent positions on a lawn or park, town trees where vegetation is scarce, and such as are not too old and fragile, may be dealt with within certain bounds, but to doctor all diseased and hollow trees on the most approved principle in such places as Epping Forest or Burnham Beeches would be highly imprudent, whether in view of the little benefit which in many instances would accrue by so doing or of the great expense involved in such an operation.
The filling, too, must be adapted to circumstances, and to deal with the entire trunk of a hollow tree is in most cases quite out of the question, both from the point of utility and expense. Short-lived trees, such as the Alder, Birch and Poplar, or such as are liable to sudden attacks of insect and fungoid pests, and those that are unfavourably situated in mining and chemical areas, should be scantily dealt with, but the practical woodman will see at a glance which trees are best worthy of his attention and treatment.
Probably the simplest, and certainly the cheapest method of dealing with diseased and hollow trunks is to clean out thoroughly all dead and decaying matter, the interior being scraped and swept with a rough brush, so that the loose rotting wood and bark is removed. When quite dry, the interior of the trunk should be painted with one, or preferably with two coats of creosote or carbolineum, and filled up with a composition of one part of Portland cement to three of clean gravel and sand, the surface coating at the orifice containing the largest quantity of cement. A coat of coal tar on top of the dry creosote goes far in making the concrete adhere firmly to the wood.
When a fairly healthy tree is being operated upon, and when the bark is likely to grow over the exposed surface, the concrete should only be brought up on a level with the underside of the living bark; in other words, the cambium should be left free for expansion. Sometimes, brickbats, broken small, are used instead of gravel, but for various reasons concrete is preferable. The concrete surface may be prevented from cracking by applying annually a coat of paint, which, for appearance sake, may be of a similar colour to that of the bark of the tree.
In the case of a large tree in which the trunk is quite hollow, usually with a basal and top opening, the amount of cement required to fill the cavity precludes the possibility of it being employed on the score of economy, but where the hollow only extends for a comparatively short distance upwards and inwards the composition is to be recommended. When a large amount of material is required to fill a hollow stem, clean bricks broken to about the size of a golf ball may be used, but they must be packed firmly and the surface, wherever it comes in contact with the weather, glazed over with cement in order to effectually shut out dampness. Asphalt has of late years been employed in the filling of hollow stems, and is to be recommended on account of its elasticity and lasting properties.
Sometimes, the interior of a large, hollow tree stem is strengthened by crossbeams of timber, any holes which extend to the outside being carefully covered with sheet lead or zinc so as to prevent the ingress of water. A sheet of lead or zinc is, however, only a superficial remedy and should be dispensed with where filling the cavity is at all practicable. Lead, in some cases, is preferable to zinc for covering wounds in trees, as it fits into position more readily and is easily fixed.
The treatment of hollow stems without filling the cavity is in certain instances quite permissible, and can be carried out at a comparatively small cost. Broadly speaking, this method consists in cleaning out all decayed and decaying matter, painting the interior with carbolineum or tar, and, where possible, bracing the trunk from the interior by means of stout crossbars of wood and covering surface holes with lead, zinc or sheet copper. When a tree trunk is hollow from top to bottom this method is to be recommended, and stout struts placed within the cavity at various of the weaker points will go far towards preserving many an aged specimen. When the cavity in a hollow stem is so large that a person can enter it, the work of either filling with a suitable composition or supporting with wooden struts is greatly simplified.
Recent experiments have proved the value of a mixture of sawdust and asphalt for filling cavities. It is particularly valuable in cases where concrete is too rigid and unyielding, such as in dealing with trunks and branches that are apt to be swayed about in stormy weather. The materials are dry sawdust, that of Oak, Chestnut and Beech being preferable, and solid asphalt derived from the refining of petroleum, which is at present in use for filling the interstices of street pavements in various parts of the metropolis.
For filling cavities in heavy, swaying branches, one part of asphalt to four of clean, dry sawdust will form a mixture that is non-rigid and yields with the motion of the branch in which it is inserted. In dealing with the trunk, which is more rigid and less affected in stormy weather, a larger quantity of sawdust should be used. The filling is made by stirring dry sawdust into boiling asphalt until the desired consistency is reached, and before the composition has cooled, it should be inserted in the previously prepared cavity. As in cement filling, the preparation of cavities to be filled with sawdust and asphalt should be carefully attended to, the decayed wood and all soft and rotten material being removed, and the interior surface rendered sterile by an application of carbolineum or kerosene. For wound dressings, gas tar and liquid asphalt is to be recommended, this combination forming a more continuous and elastic covering than is the case when tar or paint alone is used.
Where the cavity is small and, as is often the case, filled with water and decayed and decaying vegetable matter, the following course is recommended:—When only a few inches deep, the water can usually be got rid of by mopping it out with a sponge attached to a convenient handle, but when the hole is too deep for this method the water may be extracted by tapping, that is by boring a hole with an auger through the trunk to the bottom of the hole. A half-inch auger will suffice, and the correct spot to bore can usually be ascertained by measuring the depth of the hole. After the water has been removed the cavity must be thoroughly cleared of all decaying tissue and accumulated vegetable matter, and in order that this may be done effectually, it may sometimes be necessary to enlarge the opening so that a suitable tool can be inserted.
When the cavity has become quite dry—a matter of considerable importance—it should be treated with creosote or carbolineum and afterwards filled with concrete in the proportion of one part of cement to four of clean gravel. Ram the concrete firm so that the cavity is perfectly filled, and finish off at the orifice with pure cement in such a way that the cambium may be induced to form a growth over the edge of the filling.
A cheap but temporary method of dealing with small hollows and cavities in fruit and other trees, is to fill these with a mixture of clay and cow-dung in the proportion of two of the former to one of the latter. Knead well and apply when in the consistency of putty, cleaning and disinfecting the hollows before filling.
Supporting Heavy and Diseased Branches.—A limb requires to be braced or strengthened when from its weight and shape it is likely to get wrenched from the main stem during stormy weather, when the weight of the minor branches and foliage is too great for the strength of the limb, when the wood of the tree is unusually brittle, when trunk or limb is decayed, and when, from accident, the tree has become one-sided and lost its natural appearance.
Forked trees often require staying, as also do such as have suddenly become exposed to storms to which they have hitherto been unaccustomed. But probably in the matter of bracing and strengthening, the most important of all trees are those in our public parks and such as are contiguous to or overshadow dwelling-houses. Park trees should receive special attention in the way of making sure that limbs are secure and not likely to cause injury to visitors; while in the case of heavy branches hanging over dwelling-houses these should be carefully and periodically examined and made secure whenever it is found necessary. Should there be any doubt as to whether a limb is insecure and dangerous, a decision should be made in favour of bracing or reducing the weight by pruning.
Unwieldy and heavy limbs are most commonly to be found on isolated trees, or such as have had plenty of room for the perfect development of stem and branch. As the loss of one or more of the larger branches often mars the ornamental appearance of a specimen tree, every reasonable means should be employed to prevent such a disfigurement. By reducing the weight of a branch by pruning, or by giving support to any that are heavy and diseased by means of wires, chains or light iron bands and connecting-rods, the trouble may be averted. In all cases the object should be to unite the branches in such a way that they may offer the greatest amount of resistance to the storm, and at the same time be neither conspicuous nor clumsy in appearance owing to the operation.
Chains, though often used, probably owing to their being readily obtainable and cheap, are for various reasons to be avoided, the flat iron band lined with leather or rubber being preferable, more readily adjusted, and less likely to cut into the bark and wood. The bands, which can be made by any blacksmith, are usually 2½ in. wide, and of the shape of the branch to be encircled, each being in two parts to facilitate fixing and to allow of slackening at any future time should the necessity arise. The band is made of a larger size than the branch to be encircled, so as to allow of the insertion of a leather or rubber collar between it and the wood, the purpose of the packing being to prevent undue friction and chafing of the bark owing to the movement of the tree. The bands, whether placed around two opposite branches or the main stem and a branch, are connected together by a light iron rod and, according to the strain, may be from one-half to three-quarters of an inch in diameter. This rod, like the bands, is divided into two parts, which are connected by a swivel and screw for convenience in loosening or tightening.