536 



NA TURE 



[April 9, 1896 



another for coppice under standards, a third for high forest 

 of spruce or Scotch pine, worked on short rotations, with 

 clear cutting and planting; others, again, for high 

 forest worked on a long rotation, under the selection and 

 shelter-wood compartment systems. 



Two prominent points to be settled in a working plan 

 are to determine the rotation and the annual yield. As 

 regards the rotation — that is, the age at which the timber 

 should be cut — the requirements of the market must be 

 consulted in the first instance. It has already been men- 

 tioned, that where pit-props find a ready market, coni- 

 ferous woods may profitably be grown on a short 

 rotation of 50 to 70 years. Where building wood of 

 moderate dimensions pays best, a rotation of from 

 80 to 100 years will be more profitable. Oak timber, 

 on the other hand, takes a long time to attain a 

 marketable size, and afterwards, with advancing age and 

 increasing diameter, continues long to increase in value. 

 Where it is intended to regenerate forests by -self- 

 sown seedlings, trees must of course be allowed to attain 

 that age at which they bear good seed in sufficient 

 quantity; nor must they be allowed to remain after the 

 production of good seed has diminished. 



These considerations follow as a matter of course. A 

 more difficult question is, within these limits, to decide 

 upon the most suitable rotation. It might be thought that 

 the simplest plan would be to divide the total income ex- 

 pected during the rotation, less the expenses incurred, by 

 the number of years in the rotation, and to select that 

 which gives the largest mean annual net income. Adopting 

 the data given on page 513, which represent the growth 

 of a Scotch pine forest on land of middling quahty, the 

 mean annual net income under a rotation of 80 and 100 

 years would be as follows : — • 



2225 + 4 + 36 + 67 -t- 86 + 91 - (60 + 3 X 80) 



"So 

 3376 + 4-f 36 + 67 + 86 + 91 4-95 -1-94- (60 -h3x 100). 



27 '6 1 shillings. 



^34- 



Under this mode of calculation, which takes no account 

 of interest, the mean annual net income increases with 

 the length of rotation, and this increase continues until 

 volume- and value-increment become so much reduced 

 that they will no longer cover the increased outlay. This 

 result, however, does not agree with what has previously 

 been explained. If, as ought to be done, interest is taken 

 into account, a rotation of 80 years is that which, in 

 the case here assumed, yields the highest net rental, and 

 is hence financially the most profitable. 



The rotation to be adopted is, it may readily be 

 imagined, a fertile subject of controversy, which often 

 gives rise to animated discussions among foresters in 

 Germany. The author is in favour of what is commonly 

 called the financial rotation, under which the forest 

 capital (soil and growing stock) yields the highest 

 interest, and under which, as explained above, the soil 

 expectation value and net soil rental culminate. But 

 Dr. Schlich justly observes that purely financial interests 

 must in many cases be modified by considerations of a 

 different character. 



How the annual yield, that is the timber which may be 

 cut annually or within certain periods, is determined in 

 the case of coppice woods, has already been indicated. 

 In the case of high forest, three different systems are 

 generally followed. The first of these the author 

 designates as the allotment of woods to the different 

 periods of a rotation. A rotation of 80 years is 

 divided into four periods of 20 years each. It will serve 

 to make matters clear, if we assume the existence 

 of a normal forest with an even distribution of age 

 classes. To the first period would be assigned in 

 such a forest all woods between 61 and 80 years, to 

 the second those between 41 and 60 years, and 



NO. 1380, VOL. 53] 



so on, so that the fourth class would comprise the 

 youngest woods under 20 years. Such a regular forest, 

 however, does not exist, and what in reality is done,, 

 is to assign the oldest woods to the first period, and to 

 distribute the others according to their age, as well as can 

 be done. A number of compartments, stocked with old 

 timber, are thus assigned to the first period, and care is 

 taken to allot to each period approximately equal areas, 

 which, if there are great differences in the quality of the 

 locality, are reduced to a common standard. The woods 

 placed in the first period are then measured, their volume 

 calculated, and the increment for half the number of 

 years in the period is added. The total volume divided 

 by 20 gives the mean annual yield during the first 

 period. The cuttings in the woods assigned to each 

 period are arranged so as to suit sylvicultural require- 

 ments and economic considerations. The allotment of 

 compartments to periods can obviously Ke made by 

 volume instead of by area. In that case old woods are 

 measured, and the proper increment added. For younger 

 woods the volume, which will stand on the ground at the 

 time of cutting, is calculated from yield tables. Equal 

 volumes are assigned to each period, the oldest woods 

 being allotted to the first, and the youngest to the last 

 period. The compartments allotted to one period, 

 whether by volume or by area, will not necessarily be 

 contiguous ; they will often be scattered over the whole 

 forest. Whether the allotment to periods is regulated 

 by area or by volume, a framework must be constructed, 

 showing during which period each wood is to be cut. 

 Hence this system is commonly known as the framework 

 system. However irregular the forest may have been ; at 

 the end of the rotation its condition will approximate to 

 the normal state. Thus the system introduces order, 

 and is yet elastic, leaving sufficient latitude in the location 

 of cuttings during each period. 



The second system regulates the yield according to 

 increment and growing stock. The legitimate yield of a 

 forest during a given period in the first instance depends 

 upon the quantity of timber produced during that period. 

 During one year more should not, as a rule, be cut than 

 the quantity represented by the sum total of the annual 

 increment laid on in all portions of the forest. In a 

 normal forest, with a regular succession of age classes, 

 the legitimate annual yield is equal to the annual incre- 

 ment. In a forest, however, which, though well stocked, 

 only contains the younger age classes, the produce of 

 which is not marketable, no yield is possible, though the 

 annual increment may be considerable. Again, in a 

 forest where the older age classes preponderate, it is not 

 only permissible, but it is in most cases necessary, to cut 

 considerably more than the total annual increment. This 

 principle has long been recognised, and as early as 1788 

 the management of the Austrian State forests was based 

 upon it. When the older age classes preponderate, it is 

 proper to fix a period, during which the surplus old grow- 

 ing stock shall be removed. If this period is called a^ 

 and I the actual annual increment, then the legitimate 

 annual yield of the forest is 



_ T , actual gr owing stock - normal growing stock 

 a 

 This, which is known as the Austrian assessment 

 formula, is still used in many public and private forests 

 of Austria and Germany. Space forbids further discus- 

 sion of this and similar methods. Suffice it to say that 

 under this system no framework is needed, and that on 

 this principle it is best to determine the yield for a short 

 period only. Hence in those forests, where this system 

 has been adopted, the yield is generally determined for 

 ten years, and at the expiration of this time a new 

 working plan is made. 



The third system, which is in force in the State forests 

 of Saxony, was origmated by Cotta in 181 1, and has been 



