FOREST EXPLOITATION. 173 



things whJicli may be taken into account with advantage 

 in determining what area shall be cleared in order to 

 obtain the products required, and, in determining this, 

 good use may be made of the observations of earlier 

 students of arborescent vegetation. 



It has been found by observation that a tree does not 

 make equal increase annually throughout its growth ; that 

 it makes increase at one rate in early growth, at another 

 rate in middle life, and another after what may be called 

 its maturity ; that different kinds of trees vary, not only 

 in their rate of growth, but also in the ages at which these 

 changes in the rate of increase occur ; and that the 

 increase varies with differences in- soil, in exposure, and 

 in climatic conditions. Estimates have been made of 

 how much increase by growth might be made by different 

 kinds of trees in different situations, and under different 

 conditions ; and of the ages at which different kinds of 

 trees variously situated, would, if felled, yield the greatest 

 quantity of wood. From these it appeared, to take an 

 'imaginary case in default of an actual one, that in the 

 case of a tree which reached its maximum of growth at, 

 say 90 years of age, after which period the decay in the 

 course of a year equalled in quantity the new wood pro- 

 duced, and subsequently would exceed this, there might 

 be more wood obtained in the course of 180 years from 

 three crops felled at the age of 60 years than from two 

 crops felled at the age of 90 years ; but that wood of more 

 value per cubic foot might be obtained by felling the 

 tree at the age of 100 years, than by felling it at an 

 earlier period of growth ; and that the age- of the tree by 

 felling at which it would yield the greatesf pecuniary 

 returu, taking into account interest and compound 

 interest, and the rent of the land, might, according to 

 circumstances, be one or other of these ages, or might be 

 another age altogether. 



And thus became known also the limit beyond which 

 fellings could not be practised without destruction to the 

 fcrest, and the ages of different kinds of trees at which 



