334 Forestry Quarterly. 



Table IV. — Volume Increment Per Cent, of Model Trees 



In the mixed forest of pine and spruce, three types are recog- 

 nized, namely: i. Uniform pine — spruce mixture; 2. Pine with 

 interspersed spruce ; 3. Pine with spruce undergrowth. These 

 types with many transitions depend on soil quality, especially 

 humidity. The fresher and stronger the soil the more prominent 

 is the spruce and the more it emulates the pine in heightgrowth, 

 while on poorer, drier sites, the spruce becomes a mere interme- 

 diate or underwood. The delicacy of the reaction in this respect is 

 noticeable, and makes it difficult to secure really uniform sample 

 areas. In the same stand in the rolling country at short distances 

 and with altitude differences of only 1 to 2m, stands show these 

 variations. The differences are best brought out by reference to 

 the heights of trees. In type I, the two species have about the 

 same height. In type 2, the pine in 3 to 4 in higher than the 

 spruce ; in type 3, the difference is 5 to jm in maximum and 8 to 

 10m in average height. 



The sample plots had been chosen according to the type of the 

 stands without reference to site quality, but when afterwards 

 ranged according to average heights it was found that 15 out of 

 the 17 plots of pine-spruce forest belonged to site class I, indicat- 

 ing that only on such sites is an even-aged mixture of these two 

 species likely to persist. 



On the poorer sites, in small volumes of the average tree of the 

 more fastidious species show how little they contribute to value 

 production, and that any undergrowth which is only 30 to 50 years 

 old, becomes entirely insignificant in volume production. 



The comparison of the volumes of mixed stands with the yield 

 tables of pure stands suffers by the fact that the latter are based on 

 stands produced under regular thinning practice. In the mixed 



