A more exact, but a much more complicated, way of doing the same thing is Huber's method (1833), by which the future yield (Ya+n) of a still immature crop may be found by multiplying the present cubic contents (ya) of the latter into the future or mature yield or fall (Ya+n), shown in the average yield tables as belonging to the class of land nearest in quality to the given crop, and dividing the product by the yield or fall (Ya) which the table shows for the crop at the age a.

Here the estimate of the cubic contents is made by means of the proportion

=

Ya Ya Ya+n: Ya+n
Ya × Ya+n
=Ya
Ya

.. Ya+n='

Ya+n
Τα

while the increment for the period of n years is equal to ya+n-ya, and the average Ya+n-Ya

annual increment =

n

This equation will be the more approximately correct the nearer ya corresponds with Ya; hence the necessity for selecting the class in the average yield table which corresponds most closely to the actual cubic contents of the crop. The older the crop is, the more likely is Huber's method to give reliable results. But it is too intricate and circumstantial to be of much use in practice.

Example.-A Beech-wood is found to be 60 years old and to have 2500 cb. ft. per acre. Only the following local average yield tables are available :—

What will the probable yield of this crop be at 70 years of age? And what may perhaps be expected at 90 years of age?

crop.

Here the land of II., or medium quality, corresponds most closely with that of the

As has been previously stated (p. 310) failing more specific data, the height is one of the best means of estimating the quality of the land and obtaining the contents of a crop from an Average Yield Table. It is safer than the basal area, or the number of stems per acre, but it is not anything like an absolute factor. Two young crops may show about equal growth in height up to a certain age, and then one, owing to deeper soil, may continue growing upwards more vigorously than the other. But, for young woods, the rough estimation of contents from Yield Tables can quite well be made, whenever considered necessary; because it is only when the crops are approaching maturity that it becomes really desirable to know the cubic contents and percentage of increment.

That is to say, for young woods the present and the probable future yield can be taken direct from Average Yield Tables, while the present stock and the current rate of growth of older crops should be measured or estimated and compared with the data of the Yield Tables before these can be safely applied for estimating the future yield. In making such future estimates of yield, it is best to calculate the percentage on the cubic

yield). And, similarly,

contents at the middle of the period (present amount+future yield

2

with regard to crops about to be regenerated naturally, the crop to be harvested and the increment on it during the period of regeneration should be estimated as if coming to the 0-10 fall at the middle of the period-e.g., =5, with regeneration extending over 10 2

years, or

0-20
2

=10, with regeneration and clearance of parent standards extending over 20 years (Beech).

Estimates from actual average yield of similar crops felled on the estate will seldom be obtainable in Britain, as returns of this sort have only in rare cases been kept. But when the crops are so very irregular that Average Yield Tables cannot be used, that is the only way in which estimates can be made; otherwise measurements of sample areas must be undertaken and the total contents of the crop estimated from them.

337

THE FORMATION OF WORKING-PLANS, OR THE PRACTICAL APPLICATION OF THE THEORETICAL PRINCIPLES,

WITH SPECIAL REFERENCE TO FIXING THE FALL FOR HIGHWOODS BY
MEANS OF PERIODS COMBINING AREA AND YIELD.

1. General Remarks concerning Working-Plans or Schemes of Management.

2. Data and Statistics requisite for the Preparation of a Working-Plan.
3. The Preparation of the Scheme of Management or Working-Plan.
4. The Explanatory Report accompanying the Working-Plan.
5. Control and Revision of the Results of Working.

1. General Remarks concerning Working-Plans.-It is hardly possible for any large tract of woodland to be managed economically, and for the productivity of the soil to be fully utilised, unless the management is regulated according to a Working-Plan. Such a Scheme of Management for the woodlands should deal with all the operations of natural regeneration, sowing, planting, weeding and cleaning, thinning, felling, &c.; and its provisions should be carried out annually, unless these have been interfered with by unforeseen circumstances (windfall, &c.).

The object of the working-plan is, so far as possible, to provide for the continuous yield of annual returns of about equal extent and value, and, so far as is practicable, from about equal areas. Whilst this ruling idea is subordinated to the first fundamental principle of sylviculture-viz., that the form of management must be a truly economic method capable of maintaining the productivity of the soil-yet the details as to kinds of trees forming the crops, method of treatment of crops, and best time and manner of utilising and reproducing them, are all to a very great extent dependent on local circumstances (soil and situation, nature of local markets, &c.). Hence no hard-and-fast rules are applicable to this branch, any more than to the other operations of practical forestry.

Throughout all the State forests of France, Germany, and Austria, the whole of the annual operations are conducted in strict accordance with the provisions of such workingplans; and even in India, fellings within the Reserved Forests are not now allowed before working-plans for their administration have been drawn up and approved by the Conservator of Forests and the Local Government, then formally submitted to the InspectorGeneral, and finally sanctioned.

This important branch of Forestry has never really received much attention in Britain. When a tour was taken throughout the British woodlands in 1885 by the students of the École Forestière from Nancy, the following remarks were made by M. Boppe, who was at the head of the party, and who was asked officially if he would be good enough to submit

VOL. II.

Y

in writing his views regarding Forestry in Britain (Appendix to Report of Committee on Forestry, 1885, p. 48):

"The productive powers of the soil and of the climate have been made use of by able and intelligent planters, who have thereby enabled Nature herself to accumulate a considerable store of timber; but all this wealth is exposed to the carelessness of some, and to the ignorance of others, until the hand of a forester manages it properly and places it on the only sound economic principle of all agricultural and forest property-a constant annual revenue and a constant improvement in production. It would certainly not be fair to hold Scotch foresters responsible for the present regrettable state of affairs; for though they have for the most part admitted the inefficiency of the present system, they are powerless to effect any improvement so long as the landowners and general public have not learned to appreciate the manifold advantages to be derived from a regular and methodical management. They have to struggle against many adverse interests and hindrances, such as grazing and shooting interests, questions of routine, pecuniary exigencies, and the fancies of sportsmen from all parts of the world. . . . Let the owner of a forest, after having made a careful and detailed inspection of it, divide it off into blocks or compartments, so arranged that they should be uniform as regards conditions of soil and of planting, and then proceed to count and measure all the trees of three feet girth and upwards, classing them in categories according to their diameter. He should then open a debit and credit account for each compartment, placing on the debit side the actual volume of the standing crop, and on the credit side the volume of timber removed at each successive felling. This register should always be consulted before undertaking any forest operation. Whenever the annual fellings fall due, it will show which compartment can best support the withdrawal of timber, and which require to be left untouched. Moreover, the balance-sheet will render an exact account, favourable or otherwise, of the condition of the forest.

"Ten years of such systematic treatment would form in itself the basis of a regular forest working-plan."

2. Data and Statistics requisite for the Preparation of a Working-Plan or Scheme of Management.-To be really serviceable, any Scheme of Management must, in addition to being based upon sound principles, rest upon sure foundations with regard to area, growing-stock, and rate of growth.

Accurate measurement of the woodland area and well-demarcated boundaries are the necessary conditions for the division of the woodlands into convenient blocks and compartments.

As regards estimates of the growing-stock and of the increment of the different crops, these can in actual practice only be made approximately, unless such an amount of time, expense, and circumstantiality were to be expended on the investigations as would be out of proportion to the advantages secured by striving after an almost inattainable accuracy. What is necessary is to

determine, as carefully as is practicable under the given circumstances, the cubic contents of the mature crops coming to the fall in the next 10 or 20 years, and to make what may seem a fair estimate of the contents of the younger crops only now beginning to approach maturity.

If it is difficult to determine the cubic contents of growing timber-crops with accuracy, it is still more difficult to estimate their rate of growth correctly; and this is the reason why systems of management based mainly upon the whole growing-stock and the increment throughout the woodlands are so little suited for practical work, despite their theoretical completeness. Equal difficulty is also found in estimating the quality of land and its productivity; and though average yield-tables can very conveniently be applied to

estimate roughly the future yield of crops now still immature, yet the use of these for estimating the fall of mature crops must likewise be taken as only a rough approximation. To endeavour to correct such estimates by reducing the areas to a common standard of productivity or quality is not altogether suitable for practical work.

The recommendations made in any Scheme of Management must take the nature of the woodlands, the local conditions, and the desires and objects of the landowner fully into consideration. Even on large woodland estates, however, it is generally preferable to have several small felling-series in different parts of the estate, rather than to concentrate the annual falls merely in one or two places.

The choice of the method of treatment and of the rotation is partly determined by the nature of the soil and situation, but also to a very great extent by the circumstances of the local market for timber. In trying to accommodate the former to the latter, and to the probable future requirements of this, conditions will almost always be found necessitating some change in the existing state of the woodlands, and the recommendations made should avoid attempting to bring about a normal condition in too short a space of time. Thus the working-plan should try to avoid either bringing immature wood to the fall, or permitting over-mature crops to remain uncut. Difficulties of this sort, arising in connection with maintaining the general direction of the fellings, may best be obviated by making numerous small independent fellingseries. The prescriptions of the working-plan should be just as concise and simple as possible. Unless the proprietor specially desires this to be done, it is a mistake to go into detail, such as making special recommendations for carrying out the falls for natural regeneration, or whether reproduction should be by sowing or planting, or how and at what distances these cultural operations should take place, &c., because the carrying out of such details sometimes depends to a great extent on future circumstances (e.g., a good beech-mast year). A simple, clear working-plan is easier to understand and to follow than any scheme loaded with detail; and when details cannot be carried out, the forester and those who have to perform the work in the woods easily become sceptical of the benefits of the plan, and are apt to deride its recommendations and to take little interest in carrying them through so as to yield the best results.

In the tabular statement which forms the plan itself, unnecessary details of any sort should be scrupulously avoided. The description of each compartment should be as terse as possible. In the report which accompanies the workingplan conciseness should also be aimed at, while not neglecting special mention of such matters as the reasons for making the specific choice of methods of treatment, fixing the rotation, &c.

In estimating the fall for the next 10 or 20 years, care should be taken to avoid making too sanguine an estimate. The current annual increment should be measured as carefully as is practicable, and used as the basis of calculation only for short periods of 5 or 10 years. Comparisons of such estimates with the actual yield of similar crops that have recently been felled should be made wherever feasible; and in some cases these latter results