1<> A I'KI.MKK <>F FORESTRY. 



of the average tree may be found by dividing its cubic 

 contents by the years of its a^o. Finally, since we 

 have found the yearly increase per tree and the num- 

 ber of trees per acre, it is easy to find the average 

 yearly increase per acre. It is unfortunate that this 

 simple and easy process is not always reliable, because 

 it 5- hard to tind either an average acre or an average 

 tree! 



The yield of a forest is the amount of wood that is 

 taken from it in a iriven time. When a forest is put 

 under conservative management, one of the most 

 important steps : > to decide how much timber can 

 safely bo taken from it; in other words, to deter- 

 mine the yield. There are three principal ways of 

 doing- so. 



The first, and the least used, is to fix the yield at a 

 certain number of mature trees. By this plan the yield 

 of a certain forest mi^ht be 100 pines. 2(>0 spruces, 

 and ls<> hemlocks, each of a ^iven diameter, every 

 year. 



The second way is to lix the yield at a certain amount 

 or volume of wood. Thus, the yield of a larov forest 

 mio-ht be tixed at lO.nnn.nnn feet board measure every 

 ten vear>. and that of another smaller one at 7r>o cords 

 very year. 



The third way is to settle upon a certain number of 

 acres to be cut over yearly or once in a givon number 

 of years. By this method the yield of a forest of COO 

 acre- mirht be tixed at J acres of mat ure 1 imher a year. 



and that of another at 300 acres e very twenty-live years. 



The time between two >ucces>i\e cutting on the >aine 

 area mu-t ho lono- enough to allow the voting trees left 



