Al'RIL 2, 1896] 



NATURE 



513 



land, whether let as a sheep-walk or for shooting, is known 

 or can readily be ascertained. The same holds good in 

 the case of osier-beds, which are cut over annually or 

 every second year, and, in the case of coppice woods, which 

 are worked on a short rotation. In all these cases the 

 yield is approximately the same every year, and so is the 

 annual outlay for labour and manure. Matters are com- 

 plicated where standards are held over in the coppice, 

 and more complicated in the case of high forest. A 

 piece of high forest consists of trees which require eighty 

 or hundred years, or even longer, to come to maturity. 

 It consists of woods of all ages, and in the same wood 

 trees of different species and of different ages are often 

 found mixed. Under good management, a piece of high 

 forest, if of sufficient extent, ought to yield, year after 

 year, approximately the same quantity of timber, and 

 hence a forest under a good system of management, in 

 accordance with a well-considered working plan, is 

 analogous to a field or meadow. When this, however, 

 is not the case, it obviously is not a simple operation 

 to determine the annual yield and the capital value of 

 a forest. The annual yield is derived, in the shape of 

 thinnings and final cuttings, from certain compartments 

 this year, and from other compartments another year. 

 Data extending over a long series of years would be 

 needed to ascertain its average amount. 



It may be objected that the capital value of a forest 

 consists of two items, the value of the land and the value 

 of the growing stock ; that the former can generally be 

 estimated within narrow limits, and that the latter should 

 be calculated by adding up the market value of the timber 

 standing in each compartment. This method, however, 

 would leave out of account all young woods, which do 

 not yet contain marketable timber ; it would, in fact, treat 

 them as blanks. The result of such a proceeding would 

 be misleading, for obviously the capital value of a forest 

 depends upon the yield which may in future be expected 

 from it. And the future yield depends quite as much 

 upon the condition of the young woods, which eventually 

 are to furnish thinnings and the final crop, as upon the 

 timber which at the present time happens to be market- 

 able. 



On the assumption that a forest is worked in accord- 

 ance with a system settled beforehand, its capital value 

 and its rental can obviously be calculated with the aid of 

 yield tables. All net income, that is, the amounts ex- 

 pected to be realised by the sale of timber, less the cost 

 of cutting, carriage, and other expenses, is discounted to 

 the present time, and from the present value of all income 

 is deducted the present net value of all expenses expected 

 to be incurred upon the property. The result thus 

 obtained is called the expectation value. Starting from 

 an area not stocked, the soil expectatioi value is obtained. 

 Thus, on the assumption that Scotch pine is to be planted, 

 the soil expectation value of an acre of land of middling 

 quality, such as that to which the data given on page 512 

 relate, will be as follows : — 



the yield of several years may be anticipated, if money is 

 wanted, or if it is desired to take advantage of a tem- 

 porary rise in timber prices. These are substantial ad- 

 vantages of forest property, which make it a desirable 

 investment, and therefore justify a low rate of interest. 

 In these calculations, as well as in all others in this por- 

 tion of his manual, the author has employed the interest 

 of British Consols, that is, 2\ per cent. The calculation 

 of the soil expectation value will be understood at a glance 

 by stating the formula for a rotation of 80 years : 



_V,o + T, 



■c 1-025* 



In calculating these values, the question had to be 

 settled which rate of interest should be employed. As 

 regards security, forest property has the drawback of pos- 

 sible damage by fire, storms, snowbreak, and insects. On 

 the other hand, once placed under systematic manage- 

 ment, a forest yields approximately equal returns annually, 

 while those of fields and grass-lands vary according to 

 the seasons. Once established, a forest requires less 

 labour, and can be left alone for a time without much risk, 

 for the timber continues to grow all the same. Lastly, 



NO. 1379, VOL. 53] 



I •025'"+ ...+ Tyn .1 *025 



^' ^i-o25*«»-i "0025 



Ygo, the final yield at the end of the rotation is, according 

 to the table given, worth 2225 shillings ; the thinnings 

 at the ages of 30, 40, 50, 60 and 70 years are worth 

 T30-4, T4o = 36, T,„--=67, T6o = 86, T-o = 9i shillings. 

 These values are all prolonged to the end of the rotation, 

 and the same is done with r, the cost of formation, here 

 assumed to amount to 60 shillings, which is deducted 

 from the sum of final and intermediate yields. The dif- 

 ference is the rent yielded by the forest every 80 years, 

 that is, at the end of each rotation, and the present value 



'' -— of this perpetual rent, after deducting the 

 I -o/*" - I 



capital value of e. the annual expenses for administration, 

 taxes, &c., {e = 3s.\ represents the soil expectation value. 



All other data remaining the same, the value of S^ 

 varies with the length of the rotation adopted, and in the 

 present case its value culminates for a rotation of 80 years. 

 Obviously this is financially the most profitable rotation 

 which yields the highest net rental, 6-25 shillings per acre. 

 Under this rotation the capital value of the growing stock 

 is utilised to its full extent ; if the wood is allowed to 

 grow older, both soil expectation value and net rental 

 diminish. It will be understood that on the data here 

 assumed, it will pay to plant Scotch pine on land of 

 middling quality, if that land can be purchased at 250 

 shillings (^12 loi-.), or less, an acre. 



The method here explained can be employed to deter- 

 mine the expectation value, not only of land, on the 

 assumption that it is to be planted up with Scotch pine 

 or other trees, but also of existing forests. The expecta- 

 tion value of a normal forest, for instance, consisting of 

 80 compartments of one acre each, all of the sarne 

 middhng quality, completely stocked with Scotch pine, in 

 a regular succession of ages, the wood on the youngest 

 compartment being i, that on the oldest 80 years old, 

 would stand as follows : — 



4418 



55 4 



It must be distinctly understood that these calculations 

 are based upon assumptions, which may not in all cases 

 be reaUsed. The first assumption is that the plan 

 adopted, upon which the formula is based, will be strictly 

 carried out, that thinnings and other operations will not 

 be interfered with by fires, storms, snowbreak, insects, or 

 other damage, and that the areas will always be fully 

 stocked with even aged timber. The second is, that the 

 data of the yield tables will actually hold good in the case 

 in point. The third assumption is, that the prices realised 

 by sale of the timber, that wages and other circumstances 

 which govern the value off and r, will be, and remain, as 

 entered in the calculations. 



There is some analogy with engineering formula;. 

 These the practical engineer uses as his guide, not 

 blindly, but with circumspection and with due considera- 

 tion of all circumstances which may affect the result. 

 The difference is this, that the forester attempts to 

 express by a mathematical formula the growth of trees,. 



