SILVICS II 



by the winds. Anyone accustomed to tramp in winter must 

 have seen the snow-covered fields, though far from trees, well 

 sprinkled with birch seed. Although these light-seeded species 

 often occur in mixed forests, the heavier-seeded varieties are 

 characteristic of them and never form pure forests except under 

 particularly unfavorable circumstances. Such exceptions are 

 the summits of the trap ridges of Connecticut where the soil is 

 too scant to support any tree life except a very open, pure forest 

 of chestnut oak. 



There are, of course, artificially pure forests, as those which 

 are planted, or those from which all but one species have been 

 removed. This brings us to the question which has been pro- 

 lific of discussion among foresters, as to whether pure or mixed 

 forests are more profitable. 



Naturally there are advantages in a mixture of deep and 

 shallow-rooted trees, since a greater store of soil moisture and 

 fertility is thus made available. So also different trees having 

 somewhat different requirements as to chemical or physical 

 properties of soil can abstract more from a given area than could 

 one species, and a mixture of trees having different degrees of 

 shade endurance can dwell more closely and form a heavier stand 

 per acre. But the chief advantage of a mixture is in case of some 

 catastrophe which devastates one species but spares the others. 

 The tamarack may suffer from insect ravages, as was the case 

 twenty years or more ago. If other species are in mixture they 

 remain to take up the area, to reproduce, and also, to some extent, 

 to present a barrier to the invasion of insects. In case of a 

 severe windstorm, the more shallow-rooted trees may be over- 

 turned in exposed situations, unless protected by a mixture of 

 windfirm varieties. So against all forest enemies a mixture 

 forms a safeguard. There is also a financial advantage in raising 

 mixed forests. The length of time required to grow timber is 

 so great that it is impossible to predict what species will be more 

 valuable by the time of maturity. In Europe the first forestry 

 measures were induced by a scarcity of fuel wood in the vicinity 

 of the large cities. Hardwoods were, therefore, cultivated in 



