by MARK L. ANDERSON, Professor of Forestry, University of Edinburgh, Scotland
The artificial establishment of new forests, or reestablishment of former devastated forests, constitutes one of the most important tasks of modern forestry. Moreover, artificial restocking is also commonly practised in forests which have for long been run under scientific management, wherever natural restocking is inadequate or, for some reason, impossible.
Until relatively recently and, so far as is known, without exception, artificial regeneration has been planned in such a way that the units employed in the process of planting or of sowing -whether that unit has been a single tree or a clump or group of trees or a quantity of seed-have been uniformly distributed according to some regular pattern over the area to be regenerated and in such a way as to ensure that the whole surface can become covered as quickly as possible with a complete canopy, lacking gaps or openings.
So much stress has usually been laid on the need for ensuring this regularity and completeness that it has become the normal practice to beet, repair or fill in, during the early years of the stand, all or most of the gaps due to the death of individual plants used in the initial establishment.
Yet the process of natural regeneration as it goes on in the natural forest, or as it is guided under those silvicultural systems which make use of the ability of forest stands to reproduce themselves by seed, almost always results in a structure of stand which is very far from being such that the individual trees are evenly spaced all over the ground. It is normal for the young stand not only to be slightly uneven-aged, but to consist of individuals very irregularly distributed. Dense groups composed of numerous individuals are scattered about, interspersed with isolated single trees and with many blank areas of varying extent.
As time goes on these irregularities tend to disappear as the individual trees become larger so that they not only eliminate many of their smaller rivals but spread their crowns over the small areas of unoccupied ground. Ultimately the whole stand may assume great regularity of spacing but may not necessarily consist of trees of uniform size, stem-form, crown-shape, branch-size or knottiness, nor of uniform stability. These attributes must vary according as the now mature trees have grown originally in isolation or as members of dense groups.
In the managed forest it is, of course, possible, by tending fellings, to influence the development of such a stand and to alter favorably the proportions of desirable and undesirable trees. It is, in fact, much easier to carry out this operation in stands of such a structure than in those which are formed by the hitherto orthodox regular planting methods. The mere fact that the trees in an orthodox stand are evenly spaced means that the thinning operation must follow a rigid pattern and that it is very often impossible to remove undesirable stems because their absence will leave too large a gap and result in loss of production and of stability. Where there are dense groups of stems in a stand, there is a much greater choice in making tending fellings and it is much easier to ensure that the area originally occupied by a group will at later and mature stages carry at least one good stem.
Further, observations of the type of stem produced in natural forests-with small taper, absence of knottiness and of coarse branches-led many foresters to assume that if trees of similar high quality were to be grown in artificial stands, close spacing was essential. In the last century, for example, close spacing were the general rule in planting operations. This had no obvious serious consequences on poorer sites where the rate of growth happened to be slow and where growth was often irregular, or on deeper soils with stable deeprooting trees. When fast-growing species came into more general use, however, and especially where there were shallow-rooting trees planted on thin soils, the stands produced by regular spacings of from 1 to 1¼ meters quickly became very unstable, and it was often impossible to lead them safely on to saw-timber size.
The reaction to this, as well as to the very high costs in these days of planting so many trees to the hectare, has been to increase the spacings to 1.5, 1.75 or even 2 meters. This has certainly increased the stability of stands but it has depreciated the quality of the timber produced and that in turn has led to the modern cult of artificial pruning, with all its attendant disadvantages.
It would appear, therefore, that any attempt to imitate the methods of natural reproduction by means of a uniform spacing with short intervals between the stems is likely to fail. Once it is accepted, however, that natural reproduction does not mean any such thing but that in the initial stages of a natural stand the keynote is great irregularity of spacing, it becomes desirable to modify artificial methods to resemble more nearly those of nature and this is the main object of the recently proposed method of spaced-group planting, the basis - of which is an acceptance of the fact that trees grow best in dense groups but that to achieve this economically it is necessary to leave a proportion of the planting area unstocked for a longer or shorter time. The method proposed is one of dense groups, widely spaced.
So far as is known, the first suggestion that some method of planting by means of dense groups widely spaced might be the subject of experiment was made by the writer in 1928 (4) in the following words: "It is suggested that if first-class timber is to be produced, trees must be grown as closely as possible, consistent with sound economy; that the best way of economizing is not to increase the planting distance from 3 feet to 6 feet (0.9 to 1.8 m.) or more... but simply to increase the average planting distance by an equivalent amount and to achieve this by instituting a method of planting in dense groups. The trees in the groups may be only from 2 to 3 feet (0.6 to 0.9 m.) apart, but there would be large gaps between the groups not planted at all, etc."
Suggestions were then made on how this theory might be applied and the possible advantages of the method were discussed, in a subsequent paper by the writer in 1930 (1), supplemented by a third paper in 1931 (2) which suggested additional possible advantages in the method.
During the years from 1929 to 1932, while the writer was employed on research work by the Forestry Commission, quite a number of experiments were laid down for a variety of purposes, in which the planting was done by means of dense groups, widely-spaced. A few experiments were even carried out to compare different group structures and spacings. Some of these experiments have been reported upon recently (3) and the results to date discussed.
During the period of the writer's service in Ireland a considerable number of small areas were planted in several forests by the new method, mostly with the object of testing its utility in the growing of broadleaf trees with conifer nurses. These areas which were planted for a period of years beginning in 1934 remain to be examined and reported upon.
In addition to these areas established by State services in the British Isles, a very few small areas were planted by private forest owners, soon after the idea was mooted. In addition, the Director-General of the Belgian Forest Service, M. Turner, adopted and adapted the idea in his technique of conversion of even-aged, pure stands to mixed irregular stands in the Ardennes (5) and also applied it to a small area he himself owned. Apart from this, little interest appears to have been taken in the proposed new system. It was stressed initially, however, that a good deal of experiment would be required before the best application of the system could be evolved, and that it would have to be varied according to circumstances.
A period of over 20 years has now elapsed since the method of planting by means of dense groups widely spaced was first tried out and, while it is still too soon to draw definite conclusions, the stage has now been reached where it is possible to recommend that it might be much more widely tested out. It is a very flexible method with infinite possibilities for modification and the time has come for appealing for a wider interest in its use. The writer is grateful for this opportunity for spreading the idea over a wider field.
The spaced-group method is based on two fundamental principles, namely: (a) that the planting unit should consist of a group of trees and not, as in the orthodox method, of one tree only or of one small pinch of seed when sowings are employed; and (b) that the planting units should be so spaced over the planting area that a considerable proportion of that area remains unstocked and is left unplanted between the units.
Within the system there can be variations of procedure of five different kinds, namely: (a) of the number of trees constituting the planting unit; (b) of the composition of the planting unit; (c) of spacing between the individuals within the planting unit; (d) of spacing between the planting units; and (e) of mixing pure planting units.
In addition, there can be a wide variety of combinations of all these variations, which justifies the claim that the system is a very flexible one.
The possible variations of procedure which the system permits may be briefly considered.
Number of trees in the planting unit
Since it would clearly be economically disadvantageous that use of the new system should require a greater number of plants initially per hectare than the orthodox system, it is useful to begin by assuming that no more plants per hectare should be used than under the orthodox system. A widely accepted maximum spacing for Scots pine is probably one of 1.25 m. x 1.25 m., and for the faster-growing conifers one of 2 m. x 2 m. These distances correspond to 6,400 and 2,500 trees per hectare respectively. If we hope to find one tree from each planting unit in the final stand at maturity and if we expect to have the whole area completely covered by an unbroken canopy of mature trees, then our conception of the minimum number of mature trees necessary to ensure this must fix the maximum possible number of trees per planting unit. For example, if we think that the final stand on a certain site should contain at least 400 stems per hectare, then the maximum possible number of trees per group will be 16, or if we think that the final number of trees of Douglas fir must be not less than 200 per hectare, then the maximum possible number of trees per group will be 13.
Most of the experiments with the system so far carried out have made use of planting units with 13 plants, but there are already indications that with some species and on certain sites, this number is not adequate, at least with a uniform spacing within the group. It may be necessary, therefore, in order to secure the fullest advantages of the method to have not less than 21, 25 or even more trees per unit, which will, of course, mean unusually high costs of establishment.
If we assume for the moment that 25 individuals per unit or group is the maximum number desirable under all conditions, and, further, that the unit must have a symmetrical structure-although this is not necessarily so-it would appear that seven possible combinations of individuals are possible, namely groups with 3, 5, 9, 13, 16, 21 and 25, planted as shown in the following diagrams:
Figure 1
Groups of 3, 5, or 9 may be discarded, except where small groups of nurse species are to be introduced throughout a principal species, or possibly as recently suggested (4) when the method is to be used in establishing irregular stands as the risk of some trees other than the central one becoming dominant and forming the final stand is too great. Moreover, the groups are not large enough to ensure that light from outside the unit will be effectively cut off while the trees are young, so that branch development is unlikely to be much reduced in comparison with the orthodox planting methods. The unit with 16 trees may be discarded as it has no single central tree and the four inner trees are likely to compete too strongly with one another. This leaves the units with 13, 21 and 25 trees as the most likely ones for general use. To them may be added another symmetrical planting unit, composed of 37 trees, with three central rows of 7, two rows of 5 and two rows of 3, which may have its uses with certain species under certain conditions.
It will be seen that if symmetrical groups are to be stipulated then the shape of each planting unit is fixed by the number of trees in it. If the spacing within the unit is not the same in both directions, the shapes may be distorted and become elongated in one direction or another.
Composition of the planting unit
In composition, the planting units may either be pure consisting of one species only, or mixed consisting of two or more species. When the species are to be mixed within the groups themselves there is a variety of ways in which the species may be combined. Experience so far has shown, however, that intimate mixtures of this nature are going to be very difficult to handle, at least when there are few trees per unit and spacing within the unit is short.
Among the number of possible combinations of two species in mixture, the following are suggested with 21-tree and 25-tree groups:
Figure 2
How and when these various forms of mixtures might be applied opens a wide field for experimentation. Much will depend upon the relative rates of growth of the two species, on the site and on the functions which the species are expected to perform. The use of outer rows of soil-improving species or of species which will follow up after and clean the stems of the principal species should be possible. It is particularly desirable to ensure that the slower-growing species on a given site is not placed in the interior of units. The use of spreading trees on the outside of units will accelerate the covering over of the inter-unit spaces.
Spacing between individuals within the planting units
Unless serious disadvantages can be shown, it is clearly desirable from the point of view of ease and cheapness of planting that the spacing of the trees forming a planting unit should be uniform throughout the unit.
Further, it is clear that the spacing between planting unit centers and the number of trees in the longest row across the unit must determine the maximum possible spacing within the unit. For example, if the spacing between group centers is 5 m, as there are four spaces of 1 m. in the center row of a 13-tree group planted at a spacing of 1 m. x 1 m. within the group, the interval between the outermost trees of two adjacent groups is 1 m, and to increase the spacing within groups will cause an overlap of the groups. In this case, then, we are restricted to using spacings within units of 1 m. or less.
The shortest practicable spacing within the group is probably one of 30 cm. x 30 cm., but some intermediate length will normally be better, say 50 cm. x 50 cm. Or 75 cm. x 75 cm. Spacings of 1 m. x 1 m. and over will not, under normal European conditions and with the common European species, ensure the satisfactory killing of the lower side-branches and the clean boles which it is one of the main objects of the method to achieve. With fast-growing trees, the above spacings can be increased in proportion to the spacing between group centers.
However, where the initial rate of growth of the species in good sites is fast, it has been found that suppression of the inner circle of trees often takes place very quickly so that they soon cease to play any part in the competition necessary to remove the branches. The outer trees tend to become more dominant and the final stand thus tends to become composed of coarse branched stems. It is now proposed, therefore, (3) to vary the spacing within the units in such a way as to give the inner trees a better chance of survival while leaving the competition amongst the outer trees intense. The suggested unit structure for groups of 13, 21 and 25 trees is as follows:
Figure 3
The symbol "ö" indicates those trees from which at least one clean-bored dominant would be expected for the mature stand. The two spacings used in these planting units might be 75 cm. for the shorter and 1 m. for the longer, or 1 m. for the shorter and 1.25 m. for the longer, and so on.
So far, no experiments have been planted with this form of unit-structure, which will make rather higher demands upon the intelligence of the workers when planting. It may be said here, however, that no difficulty has been experienced in getting workers to plant by the new system, provided the plants are taken to the area in bundles of 13, 21, 25, etc. All that the worker has to do is to locate the unit center, which he can do with a light stake and he then distributes his bundle around the stake in the manner required. Needless to say, in normal forest practice, absolute accuracy of spacing and shape and position of group are not essential.
In general, the spacing within the group will vary to some slight extent with the species, the site and expected rate of growth and the composition of the group, but it will make planting easier if such variation is kept to a minimum. The greater the number of trees in the planting unit, the shorter the spacings within the unit can be; competition will be keener but there is a better chance for one or several clean-stemmed dominants to develop than is the case in units of smaller numbers. In the trials made so far the commonest spacing has been one of 2 ft. x 2 ft. (60 cm. x 60 cm.) but spacings of 3 ft. (90 cm.) and of 1½ ft. (45 cm.) have sometimes been employed, all in relation to spacings between unit centers of 12, 15, 18 or 21 ft. (3.6, 4.5, 5.4 and 6.3 m.).
Spacing between the planting units
There are two things which require to be taken into account in determining the spacing between the planting units, namely, that the number of trees to be planted per hectare should not exceed the number used in orthodox regular spacing, and the number of mature trees expected per hectare when the stand reaches maturity. If it is stipulated that the same number of trees is to be used per hectare as with present planting methods, then with a group having a fixed number of trees, 13, 21, 25, etc., spacing between unit centers will depend directly upon the number of trees per hectare allowed. Table 1. shows this relationship.
TABLE 1. - RELATIONSHIP BETWEEN ORTHODOX PLANTING DISTANCES AND UNIT-SPACINGS
|
Planting-distance by orthodox systems (cm.) |
Stems per hectare |
New system, no. of groups per ha. |
Spacing between unit centers (approx.) |
|
13-tree unit |
|
|
|
|
75 X 75 |
17778 |
1368 |
2.8 X 2.8 |
|
100 X 100 |
10000 |
769 |
3.6 X 3.6 |
|
125 X 125 |
6400 |
492 |
4.5 X 4.5 |
|
150 X 150 |
4444 |
342 |
5.5 x 5.5 |
|
21-tree unit |
|
|
|
|
75 X 75 |
11778 |
846 |
3.5 X 3.5 |
|
100 X 100 |
10000 |
476 |
4.6 x 4.6 |
|
125 X 125 |
6400 |
305 |
5.7 x 5.7 |
|
150 X 150 |
4444 |
212 |
6.8 X 6.8 |
|
25-tree unit |
|
|
|
|
75 X 75 |
17778 |
711 |
3.7 X 3.7 |
|
100 X 100 |
10000 |
400 |
5.0 X 5.0 |
|
125 X 125 |
6400 |
256 |
6.2 X 6.2 |
|
150 X 150 |
4444 |
178 |
7.5 x 7.5 |
If, on the other hand, it is stipulated that there must be at least 250 mature trees per hectare, which is equivalent to a spacing between unit centers of about 6.3 meters, then the number of plants required to give 250, 21-tree or 25-tree units per hectare will exceed the number required with an orthodox spacing of 1.5 X 1.5 m.; it will be almost the same number in the case of 25-tree groups as that required with an orthodox spacing of 1.25 X 1.25 m.
The range of spacings between unit centres allowable will in general be found to run from 4 m. x4 m. to 7 m. x7 m., corresponding to 625 units and 204 units per hectare respectively.
The actual extent of ground left unplanted between the planting units depends not only on the spacing between the unit centers, but also on the spacing between the individuals within the units. The wider this spacing is, the smaller is the unplanted area between the groups.
Table 2 demonstrates what the unplanted intervals between the outer trees of adjacent units (Y), and what the unplanted areas of ground enclosed by four adjacent units would be at different spacings between unit centers and at different spacings within the units (B). This is shown in greater detail for 13-tree planting units, with which the inter-unit areas are octagonal in shape. The area enclosed by the bases of the exterior trees of each unit is also given for comparison (A).
TABLE 2. - INTERVALS AND UNPLANTED AREAS BETWEEN PLANTING UNITS AT VARIOUS UNIT SPACINGS (x) AND PLANTING DISTANCES WITHIN THE UNITS (Z)
|
Spacings between unit centers (X) |
No. of units per ha. |
No. of trees per ha. |
Planting distance within units (Z)(cm.) |
Area covered by each unit (A)(m.2) |
Interval between outside trees of units (Y)(m.) |
Inter-unit area not covered by trees (B)(m.2) |
Ratio B/A |
|
13-tree unit, old style |
|
|
|
|
|
|
|
|
4X4 |
625 |
8125 |
50X50 |
2.0 |
2 |
14.0 |
7.0 |
|
,, |
,, |
,, |
75X75 |
4.5 |
1 |
11.5 |
2.6 |
|
,, |
,, |
,, |
100X100 |
8.0 |
0 |
8.0 |
1.0 |
|
5X5 |
400 |
¹5200 |
75X75 |
4.5 |
2 |
20.5 |
4.0 |
|
,, |
,, |
,, |
100X100 |
8.0 |
1 |
17.0 |
2.2 |
|
,, |
,, |
,, |
125X125 |
12.5 |
0 |
12.5 |
1.0 |
|
6X6 |
278 |
¹3614 |
75X75 |
4.5 |
3 |
31.5 |
7.0 |
|
,, |
,, |
,, |
100X100 |
8.0 |
2 |
28.0 |
3.5 |
|
,, |
,, |
,, |
125X125 |
12.5 |
1 |
23.5 |
1.9 |
|
7X7 |
204 |
¹2652 |
75X75 |
4.5 |
4 |
44.5 |
9.9 |
|
,, |
,, |
,, |
100X100 |
8.0 |
3 |
41.0 |
5.2 |
|
,, |
,, |
,, |
125X125 |
12.5 |
2 |
36.5 |
2.9 |
|
,, |
,, |
,, |
150X150 |
18.0 |
1 |
31.0 |
1.7 |
|
21-tree unit, new style |
|
|
|
|
|
|
|
|
6X6 |
278 |
5838 |
100X75 |
11.1 |
2.5 |
24.9 |
2.2 |
|
7X7 |
204 |
4284 |
,, |
11.1 |
3.5 |
37.9 |
3.4 |
|
25-tree unit, new style |
|
|
|
|
|
|
|
|
7X7 |
204 |
4284 |
,, |
15.6 |
2.0 |
33.6 |
2.2 |
|
37-tree unit |
|
|
|
|
|
|
|
|
7X7 |
204 |
7548 |
75X75 |
15.8 |
2.5 |
33.2 |
2.1 |
¹) Due to overlap of units there should he reductions in the number of trees required by about 500, 360 and 220 per ha. respectively in these three cases.
The last column shows what proportion of the ground is not covered by trees in relation to the area which is, at the time of planting. As the trees grow, however, and develop their side-branches, the ratios given will gradually be reduced, until ultimately the whole ground surface becomes over-shaded with foliage. The period which will lapse before this occurs will depend on several factors, but mainly on the species and the rate of growth.
These unplanted inter-unit spaces are extremely important and are an essential feature of the method. They offer certain important advantages over the ordinary orthodox regular planting method.
Mixing of pure planting units
As already mentioned, the system lends itself to the mixed planting of species in two ways. The mixing of the species within the planting unit itself has already been briefly touched upon, but the species may also be planted in pure groups and mixed by groups, all trees in some groups being of one species and all those in others of another species. Such a mixture may be regular after some definite pattern, as is usually the case when a single tree is the planting unit, or it may be irregular and in such a way as to ensure that the two species are distributed to make the best use of uneven ground and varying locality conditions. For example, units of spruce will be placed in wet hollows and units of pine on dry ridges, or the mixture of units may be done regularly simply to ensure that trees of both species will occur in the final stand.
A further useful possibility, however, is that of being able to mix units of different structure, when the function of the two species to be mixed differs; for example, when one species is included merely as a nurse for a more valuable main species. It is very seldom that a stem-by-stem mixture of two species by the orthodox regular planting method is a success. The two species seldom grow at the same speed on all localities and so one has to be specially helped against the other. The general tendency nowadays is to mix species either -by lines of three rows each or of five rows each or by small pure groups, in such a way that no part of the ground is unplanted. A favourite group size or planting unit is one of nine trees.
The proposed new method of planting dense groups, widely spaced, lends itself very well to mixing a main species with a nurse species, and offers possibilities of reducing the costs of establishment. This reduction can be achieved by mixing small units of the nurse species with normal units of the main species. These small units may consist of 5, 3 or even of single trees, thus:
Figure 4
A further advantage of the method in the growth of mixtures is that the faster-growing nurse-tree units can be removed after they have fulfilled their purpose and can be replaced by the main species or by another secondary species to act as a soil-maintainer or a follower. For example, European larch grown as a nurse for oak might be removed and replaced by beech, leaving a mixed oak-beech stand with the oak well ahead.
A further illustration of the flexibility of the method is that it results in a stable stand structure, from which whole units can, if desired, be removed after they have reached small pole and utilizable size and can be replaced with whole units of a new species, which may be a tender shade-bearer requiring shelter which the remaining units supply. This procedure is now being tested.
The method of planting by dense groups, widely spaced, has been criticised on the grounds that it is a difficult method to apply in practice. In fact, however, this has not proved to be so, although it certainly requires a little more thought and supervision than the simpler orthodox method. The main difference is that the planter has to locate the unit center in addition to the location of each tree. This disadvantage is more than offset in subsequent beefing and liberating operations, for it is easier to locate a group than single trees.
When the new system was first mooted, it was found very difficult to convey any clear impression of what a plantation established in the manner suggested would look like. In the past 25 years, however, many of the trial plantations have developed sufficiently to provide useful illustrations of the general appearance of planting units and stands in the early stages. It is stressed that it will still be many years before the final form of stand can be known.
A selection of photographs taken in existing stands has been made to bring out certain points and to convey to those who have not seen actual examples what such plantations look like before the thinning stage.
In all cases shown, the planting distance within the units was approximately 60 cm. by 60 cm.
It will not be possible to discover the full advantages and disadvantages of the proposed new system of planting by means of dense groups, widely spaced, until the plantations established by this procedure reach maturity, and until the full scope of the possible combinations and modifications has been fully tested out over as wide a range as possible. This is a very long-term project.
Meantime, however, it has already given certain indications of likely advantages and disadvantages. A few of these may be said to be definitely proved already, others can only be surmised or anticipated. They may be considered under these two categories.
Proved advantages
1. The type of stand-structure produced greatly increases freedom of movement and action throughout the stand, so that inspection, tending, extraction, drainage, soil cultivation and all operations subsequent to planting are greatly facilitated.2. The type of stand-structure produced is of particular value on steep and very steep slopes, for it not only allows ease of extraction of early thinnings without damage to the retained best stems, but also allows the survival of a higher proportion of trees with symmetrical crowns in the mature stand.
3. The type of stand-structure produced is in the early years more stable and stronger than that produced by close or moderately close normal spacing and this allows greater flexibility of treatment, for it permits altering or improving the composition and increasing the irregularity of the stand, should this be desired - in protection forests and stands, for example-without undue risk of storm damage.
4. Where intensive methods of soil preparation and of manuring are needed to give trees a boost to carry them over the first difficult years on poor sites, a satisfactorily established stand can be ensured by concentrating the costly special operations only to the small areas on which the dense groups are to be planted. This may mean a considerable reduction in costs of establishment.
5. Similarly, in areas of short scrub which is expensive to clear, a satisfactory stand can be obtained on certain sites by confining the scrub-cutting to small-spaced gaps, into which the new species can be introduced in dense groups.
Probable advantages, not yet proved
1. It seems to offer distinct prospects of the production of straight, clean, branch-free stems, pruned naturally, at a cost no higher than in methods employing normal average spacings and with less risk of producing unstable stands.2. The type of stand-structure allows greater choice of elite stems for the mature stand, so chosen that they completely cover the whole area.
3. The system is well adapted for use in planting mixtures, especially if the species are planted pure in the groups. It can be modified so as to make the best use of nurse species without harm to the main species and can be used to bring in secondary species or underwood in such a way that the latter are not too greatly subject to over-head shade.
4. The stand-structure produced probably allows greater delay in the making of thinning without risk to the stability of the stand.
5. Under certain conditions, snow damage at high altitudes may be reduced.
6. The stand-structure produced seems to be specially well-suited for the formation of shelter-belts and protective margins to forest areas. In this connection attention may be drawn to the recently advertised Russian method of "nest" plantings and sowings, recommended for shelter-belt planting, which is essentially similar.
Probable disadvantages
1. In the early years there is probably a greater fire-risk in plantations of this form, because of the greater amount, for a time, of withered herbage in the unplanted inter-spaces.2. There is a risk, under certain locality conditions, of the outer trees of the units developing more vigorously than the inner and becoming dominant. As these will normally be more coarsely branched than trees planted at normal average spacings, a stand with inferior timber will result. This tendency can, however, probably be controlled by suitable planting unit structure and by proper thinning technique.
3. To get satisfactory clean timber it may, under certain circumstances, be necessary to plant more trees per hectare than by an orthodox technique using wide spacings, and this will add to the costs of establishment. This extra cost may or may not be balanced by improved timber value plus the other advantages of the new method. That remains to be studied.
The proposed method of establishing plantations by means of dense groups or planting units of various composition and structure, widely spaced between their centers, represents a radical break-away from the normal, accepted practice of planting the individual trees at regular spacings all over the area. It appears to offer very important advantages over the orthodox method, in particular from the fact that an essential feature of the method is to leave at least half of the planting area unplanted between the groups.
While trials of the system to date only touch the merest fringe of the possible variations, they are already promising and it is thought very desirable that more wide-spaced experimentation should be carried out on the same lines. The object of this article is to draw wider attention to what is, after all, a very simple idea, in the hope that world-wide trials of the system may be initiated and that positive results will be obtained which will lead to improvements in silvicultural technique concerned with artificial regeneration and afforestation. While the writer is unlikely to see the final outcome of the first trials, he would wish to express his thanks to the State Forest Services of Great Britain and Ireland for enabling him to initiate these trials and for allowing him to study their later development and to report thereon.
1. ANDERSON, M. L. - A New System of Planting. Scottish Forestry Journal, Vol. 44 (2). 1930. pp. 7887.
2. - Planting in Dense Groups Spaced at Wide Intervals. Quarterly Journal of Forestry. Vol. XXV (4). 1931. pp. 312-316.
3. - Spaced Group-planting and Irregularity of Stand-structure. Empire Forestry Journal. Vol. XXX (4) 1951.
4. KAY, J., AND ANDERSON, M. L. - Douglas Fir at Home and Abroad. Empire Forestry Journal, Vol. 7 (1).1928.
5. CAMERON, R. D. - A Study of the Development in Plantations of Small, Closely-planted Groups with Wide Interspaces. Manuscript in the Imperial Forestry Institute Library, Oxford. 1950.
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