CHAPTER XIV

THINNING PLANTATIONS

In the successful rearing of timber trees for profit there is, perhaps, no other branch of more importance than a good knowledge of the art of thinning, and, at the same time, one on which so great a diversity of opinion exists.

Thinning plantations, be they old or young, must always be subject to great modification, according to the nature of the trees and soil, or ultimate design of the plantation being operated upon, and is a matter requiring great tact, forethought, and discrimination, and this can only be acquired by long experience and by those having a good insight into the peculiarities and properties of our forest trees.

The same rule as regards thinning will not apply to, say, fir, hardwood, and mixed plantations; and far less will it hold good in the case of an ornamental and a profitable wood. No universal rule can, however, be laid down for thinning, but general principles can be given that will be sufficient for the guidance of those who have to undertake such work.

In thinning any plantation two important points are to be borne in mind—first, cut away all diseased, dead and dying trees; second, study the relationship of trees and soil, and act accordingly. To be more explicit, we might say that in the first case, the removal of all dead and dying trees is a necessity, and that being done, one can proceed with the disposal of the standards to be left. In the second case, by suiting the trees to the soil, at least as far as possible, great benefit results, and an instance of this that came under our own observation lately will be given as an example. A plantation 130 acres in extent was composed of oak, larch and Spanish chestnut, placed at regular distances apart throughout the whole extent of the wood. Now, the soil was gravelly for a considerable distance down, and, consequently, fairly well suited for the chestnut, but just the reverse for the larch, which, on such a soil, generally becomes “pumped,” or rotten at the core. In thinning this particular plantation, it would have been very unwise to cut away the chestnut and the oak and leave the larch, and this had happened to some extent before the proper system of management and adaptability of soil to tree was thought of. Larch may look healthy enough, and show but small indications of disease, even when growing on gravel up to twenty or thirty years of age, so that it is with difficulty that the inexperienced become aware of the pending doom that usually awaits this tree when planted on such a soil. This example is merely given to point out how carefully thinning should be gone about, and that in all cases it is a wise policy to study soil in relation to the future crop of timber before an axe is laid to the tree.

At the outset of these remarks on thinning plantations it should be distinctly borne in mind that there are two chief objects for which trees may be grown, each requiring a special mode of management, in order that the best results may be obtained.

The first is their management in a purely economical sense or with a view to profit; the second, their management with a view to ornament. There is also a third object that is well worthy of consideration, and that is the growing of timber in one and the same wood, both for ornament and utility combined, and this is very frequently the case with home woodlands that are visible from roads and drives, with strips bounding parks or pleasure-grounds, and on small properties.

To produce ornamental trees of natural appearance is by no means difficult, as by allowing the individual specimens ample room for branch development, the desired effect is gradually brought about. Far greater difficulty, however, attends the production of the greatest quantity of the most valuable trees on a given space of ground. Here many questions of the greatest moment, on which difference of opinion exists, crop up: such as at what age thinning should be commenced, to what extent should it be engaged in, what time should elapse between each thinning, and which trees should be removed.

[Illustration: FELLING TOOLS.]

Any one at all interested in the management of our woods and plantations must have noticed that trees having an abundance of room and light on all sides make comparatively short and thick trunks that are well furnished with branches; whereas such as are grown up in a circumscribed space and amongst others are tall and straight, with clean, well-formed stems destitute of branches for the greater part of their height. All species, or nearly all, are governed by the same laws, that is to say, those that have the least room laterally within certain prescribed limits, which will be described hereafter, produce the tallest, cleanest and straightest trunks, and vice versa.

The influence of light has not, in this country at least, been sufficiently taken into account in the rearing of timber, but it has everything to do in directing the growth of trees, and should be reckoned as a most important factor by the forester. Thus, if it be allowed in excess, as when the trees stand far apart, the growth of lateral shoots and large branches will be greatly induced, the result being short and thick boles, that are rough and knotty, and ill-adapted for constructive purposes. On the other hand, by keeping the trees thick on the ground, light is, to a greater or less extent, excluded, and the trees grow tall, straight and branchless for the greater part of their height, and are of the greatest economic value. But here another and very important question crops up. To what extent in a wood, managed solely for the value of the timber it produces, will it be profitable to thin? In dealing with this, two distinct bearings should be kept in mind—the first, that too small a quantity of branches and consequently of leaves, must, to a greater or less extent, check the growth of the trees, and so diminish the production of timber; and, second, that by having too large a quantity, the value of the timber is greatly reduced in consequence, and the number of trees to the acre much diminished as well.

There is, therefore, a medium between these two, by adopting which, the greatest quantity of the most valuable timber will be produced; although, at the same time, it is astonishing, when looked at from a physiological point of view, what a small quantity of foliage is required to keep a plantation tree in a healthy, growing condition, and to produce a trunk of useful dimensions. This may, however, be explained by the fact that the almost entire absence of large limbs and branches, which in some cases would amount to one-fifth the total bulk of the tree, renders the amount of sap, and consequently of leaves, required proportionately less, the nutriment being mainly elaborated in the building of the trunk.

Independent altogether of the forests of northern Europe, Canada, etc., which have grown up naturally, examples might be given in our own country—the native Fir forests in the Highlands of Scotland, the valuable Beech woods on the Chiltern Hills, and a few Larch plantations in Yorkshire and Bedfordshire—where trees averaging 70 ft. in height, growing at from 4 to 6 yards apart, and with only a tuft of foliage atop, may be seen. It is only, however, by long and careful study and attention to different trees at different stages of their growth that any idea can be formed of the amount of branches and foliage required for preparing the sap that will be necessary for the profitable yearly increase of the trunk until maturity is arrived at.

The questions now to be dealt with in growing timber for purely economical purposes are: (1) At what age should thinning be commenced? (2) To what extent should it be engaged in? (3) What time should elapse between each thinning? And (4) Which trees should be removed?

At the outset, it may be well to mention, that in so far as any of the above questions are concerned, no hard and fast line can be laid down as to the universal management of plantations, each tract of wood, and even different parts of the same wood, according to the particular species of tree, quality of soil, altitude, and exposure, being dealt with on its own peculiar footing. Many serious mistakes have been committed, and irreparable damage done, by treating every plantation alike and according to the rule-of-thumb method. Upon the manner in which thinning is performed, much of the ultimate success of a plantation will depend, and it is a matter requiring great tact, forethought, and discrimination, which can only be acquired by long experience, and an intimate knowledge of trees and their surroundings.

The quality as well as quantity of timber produced should be carefully considered in the management of every plantation. In dealing with the following questions regarding thinning, it may be well to state that the average plantation will alone form the basis of remarks.

=1. At what age should thinning be commenced?=—The necessity of thinning, few practical arboriculturists will care to deny, and that whether the plantation be composed of coniferous or hard-wooded trees. It is the abuse of the practice that, in this country at least, is so to be condemned, and I entirely dissent from those who consider that a coniferous plantation should be left to Nature, or, in other words, should thin itself. The argument that the natural forests of America, the source from which we derive the finest and best quality of timber, thinned themselves, is often quoted; but it should also be remembered that the conditions of such forests are widely different from those of our own, and that the waste of timber is immense, great quantities being destroyed in procuring what is required. Although, however, we cannot adopt all the details of Nature’s practice, we can and we should admit the correctness of the principle on which she acts, and by studying this we learn much, and it is by acquiring a knowledge of her economy, and where and when to apply assistance, that the point of the whole argument rests. Natural regeneration, unless it be in a limited number of cases, and particularly with our least valuable classes of timber, is never, in this country, likely to supersede artificial planting, and it has been conclusively proved in the Forest of Dean, that with our most valuable timber-producing tree, the Oak, the latter system is most to be encouraged.

No thinning of young trees should take place until a complete ground shade has been established; and it is most important for the welfare of the plantation, that a complete overhead foliage covering be brought about at as early a date as possible after planting. At what age this may take place will depend mainly on the size of the plants used and the distance apart at which they were inserted in the ground, and to a lesser extent on the quality of soil and other considerations. At a short period after a complete leaf canopy has been established, the individual trees begin to press against each other, and later on a struggle for existence commences, the stronger specimens gaining the supremacy over the weaker. Here it must be borne in mind that hard-wooded trees require proportionately more room for their healthy development than coniferous kinds, while length and clearness of stem, produced by a due proportion of shade, is an object of prime importance. It might, as some suppose, do little harm, to let the struggle for existence go on unchecked, but there can be no question that for several reasons it is wise policy to allow the stronger trees every chance of succeeding, and to cut away the weaker. The object should be to provide for the trees left standing that amount of room or growing space best suited for bringing about the particular conditions aimed at, and in thinning, it must be the aim of the forester to arrive at the happy mean—neither over nor underdoing the work, the former in particular. But while overcrowding is not to be tolerated, the danger of suddenly exposing the trees to currents of air, to which they have hitherto been unaccustomed, must be carefully guarded against, and it should be distinctly borne in mind that to thin trees in an abrupt manner is one of the greatest mistakes that it is possible to make.

Statistics compiled from a healthy Larch plantation, growing on fair soil, and in a moderately sheltered position in southern England, will now be given, from which a good idea can be formed as to the age and size when thinning should be commenced. The trees when planted were 2 ft. high, and pitted at 3 ft. apart. In four years the outer branches began to touch each other, and in six years from time of planting the average height of trees was 7 ft. 10 in. and the shade occasioned had killed out most of the grassy undergrowth. At this period of growth, the disproportion in the size of the trees was, as is usually the case, considerable, and left no doubt about which to remove when the first thinning took place. Two years afterwards, or in eight years from time of planting, thinning was first engaged in, the taller trees at that time averaging nearly 11 ft. in height, but many of the suppressed and weakly were little more than half that size. Another thinning took place during the twelfth year, and in 1911 the trees average 40 ft. in height and were standing at a distance of 9 ft. apart. The plantation referred to is on the Earl of Derby’s property of Holwood, in Kent.

=2. To what extent should thinning be engaged in?=—In following up the latter case, the tallest and healthiest trees were reserved; all distorted, sickly, and stunted specimens being removed; but in the case of two or more proportionately small trees growing in close proximity, the most promising was left, and the others cut away, thus avoiding gaps in the plantation. At the first thinning it will be found quite impossible to leave the trees anything like regular over the ground, although this should be studied as much as possible, and bare spaces are to be carefully guarded against. With the vigorous growth of the trees, and the interlacing of branches previous to the first thinning, no great openings will require to be made, and nothing more than will be canopied over during the next two years.

=3. What time should elapse between each thinning?=—This can only be correctly decided after a careful inspection of the particular wood. Generally speaking, after the first thinning, when the trees were eight years old, the lower branches gradually began to give way, and as the trees increased in height, this became more and more apparent, and formed a good guide as to the time which should elapse before the second thinning might profitably be engaged in. The intervals between the various thinnings should for the first thirty years in the case of Larch—and, indeed, most other trees—be comparatively short, but become longer with advance of age; but heavy thinnings must be carefully avoided, especially if the best class of coniferous timber is to be produced.

A well-managed Larch plantation of twenty years’ growth should have the trees branchless for about one-half of their height, which is, of course, brought about by crowding, and at forty years three-fourths of the trunk should be clear of branches.

I have purposely abstained from giving the number of feet apart at which trees ought to stand at various stages of their growth, and the number of thinnings they require, as being likely to prove misleading.

=4. The question as to which trees should be removed= need cause little or no anxiety, as the dead, dying, diseased, and badly-formed will naturally receive first attention.

In thinning, the following short rules should be observed:—

1. Thin not at all until the undergrowing vegetation has been completely killed out by the overhead foliage, the golden rule of sylviculture being to keep the sunshine off the ground until near the end of the tree’s career.

2. Thinning should be performed in such a manner as not to reduce the value of the crop, but so as to tend to the production of the greatest quantity of the most valuable timber in the shortest possible space of time.

3. By thinning allow of sufficient light and air to prevent the trees becoming drawn up and lanky, but avoid too much space, which induces the growth of side branches and detracts from the value of the timber.

4. Keep up the number of trees to the highest possible pitch until they are tall, straight and clean, and thin gradually.

5. The danger of suddenly exposing the trees to currents of cold air to which they have hitherto been unaccustomed must be carefully guarded against and it is a serious mistake to thin in an abrupt or unequal manner.

6. In thinning remove all dead and dying trees first, then the distorted and stunted, the best grown and healthiest being preserved for the permanent crop.

7. Hard-wooded trees require proportionately more space for development than conifers, and the annual rings in the timber of the latter should be narrow in proportion to those of the former, good quality of hard-wooded timber being indicated by broad annual rings, but with coniferous wood the reverse is the case.

8. Thinning should be commenced at the central or most sheltered point of a plantation, or section of same, so that the outer intact boundary may continue to form a barrier to cold winds, which might prove injurious to trees that had hitherto stood in close order.

9. In economic forestry, timber trees should be cut down when they have arrived at maturity or have ceased to grow. With coniferous trees this generally occurs at from seventy to ninety years; but with hardwoods, excepting the ash and chestnut, which are of most value, say, up to fifty years’ growth, the period may be greatly extended.

10. Thinning is usually performed in autumn and early winter, but it may be well to remember that at the latter period the lowest percentage of moisture (about 47 per cent.) is present, and the timber consequently of the greatest value for constructive purposes.