39 



SYSTEMATIC MANAGEMENT OF FORESTS.* 



THE MODEL FOREST. 



Imagine a uniformly productive tract, divided into any number (n) of 

 divisions, or compartments of equal area; the first stocked with trees one 

 year old, the second with trees two years old, and so on in an ascending 

 series up to the nth compartment stocked with trees n years old. And let 

 the revolution or age at which the trees of any compartment are to be cut, 

 be n years. The land will then be parcelled out into a number of compartments 

 equal to the number of years in the revolution and each one will 

 be stocked with trees one year older than those of a compartment im- 

 mediately proceeding it in age, so that there will be a complete series of groups 

 of all ages from one to n years old If, now, all trees n years old, that is those 

 in the nth compartment, be cut, and the land immediately restocked with young 

 growth, it is evident that, at the end of twelve months, the group of trees next 

 in order of age, or n minus one year at the time of the first cutting, will have 

 advanced to maturity, while the plants on the first coupe will have taken the 

 place of the youngest group in the series, and the plants of all intermediate com- 

 partments have advanced one year in age. At the expiration of twelve months 

 from the time of the first cutting, we may therefore again cut a group n years 

 old, and so on forever, cutting a group n years old once a year without demolish- 

 ing the standing stock. 



The yearly produce thus obtained is. in fact, the annual growth, or interest, 

 of the material standing on n compartments, and is called the sustained yield, 

 and a forest so organized is called a model, or ideal forest, because it represents 

 a state of things which is theoretically perfect, if never quite attainable in 

 practice. 



If, in the case just considered, we were to cut more than the sustained yield 

 in any year, we would be trenching on the capital stock and unable to maintain 

 an unvarying yield. If on the other hand, we were to cut less, we would not be 

 working up to the full capability of the forest and would have a certain amount of 

 capital, in the form of trees, lying idle, and for the time being unremunerative. 



A forest may, therefore, be regarded in the light of a capital producing by 

 its yearly growth a certain interest in wood, just as a sum of money which is 

 lent out produces interest ; and, in estimating the growth of a forest viewed as a 

 productive money capital the rate is calculated in precisely the same way as in 

 ordinary money transactions. 



Trees of about the same age and height, growing together in a mass, or trees 

 growing in a sub-compartment are called a group. A compartment may con- 

 tain one or more groups ; if more than one, the area occupied by each group is. 

 called a sub-compartment. The group is the smallest unit of mass, and the sub- 

 compartment is the smallest of area, in regular forests. 



THE REVOLUTION. 



The term revolution is used to donate the period of years which is being 

 fixed to elapse from the time of the production of a tree, or group, to the time of 

 its being cut down. It does not necessarily correspond to the age at which a 

 tress is harvested, because trees sometimes have to be cut, or fall from natural 

 causes, before the revolution fixed upon is completed. 



* Macgregor ; Organization and Valuation of Forests. 



