1 8 North American Forests and Forestry 



their warfare. Suppose that on a tract of land 

 covered with oak, birches, or other light-lovers, 

 the seed of beech, maple, or other shade-endurers 

 should be deposited. The light coming through 

 the crowns of the established species would be 

 sufficient to start the young invaders into vigorous 

 growth ; the seedlings would gradually develop 

 into trees, each forming its usual dense crown and 

 casting a deep shade on the ground under it. By 

 and by they will distribute their seeds, some of 

 which will grow into trees, and it will make no 

 difference to them whether they are rooted under 

 their parent species or under the neighboring oaks. 

 In either case, the light conditions are favorable. 

 But with the seeds cast by the oaks things are dif- 

 ferent. If they sprout under one of their parent 

 species they will grow. But those that come to lie 

 under the beeches do not find light enough, and 

 either do not sprout at all, or soon languish and die. 

 By and by some of the old oaks will perish, from 

 accident or age. In the new growth the beeches 

 already have the majority, and the percentage in 

 their favor is constantly increasing. After some 

 centuries the oaks will have disappeared, and in 

 place of the sunlit oak grove there now stands 

 a cool, shady beech wood. The war has resulted 

 in victory for the invader. Of course, the light 

 conditions are not the only factors to decide the 

 struggle, else the light-loving trees would long ago 

 have become extinct. It might happen, for in- 

 stance, that when the seeds of the shade-enduring 



