278 ELEMENTARY STUDIES IN BOTANY 



mulation of humus, and it is called the heath stage, for plants 

 of the heath family and their associates occupied the ground. 

 At this stage, for the first time, the plants covered the ground 

 so thickly that competition among individuals began. 



With the further accumulation of humus, the fifth stage 

 became possible, that is, the pine forest stage. Gradually 

 the pines invaded the heath, first the jack pine, then the red 

 pine, and finally the white pine. It was at this stage that 

 men caught the succession and destroyed the pines. When 

 a forest fire swept through the pine forest, it not only checked 

 the succession, but often set it back. If the fire was pro- 

 longed and intense, it not only destroyed trees, but also 

 much of the humus, and in such a case the succession might 

 be set back to the heath stage. This would mean a long 

 accumulation of humus before the pine forest could come in 

 again. 



But the important fact is that the white pine forest is 

 not the climax forest for that region, for it has the curious 

 habit of what may be called race suicide. Its seeds do not 

 germinate well and its seedlings do not thrive in the shade, 

 so that when a deeply shaded white pine forest is established, 

 it cannot perpetuate itself. But this shade is favorable to 

 the seeds and seedlings of the maple and beech, and therefore 

 these trees gradually supplant the white pine, and the maple- 

 beech forest (a hard-wood forest) is the climax association 

 for that region. It follows that the problem of forestry in 

 the white pine region is not merely a fight against the dev- 

 astation of men, but more fundamentally a fight against 

 the race suicide of the white pines and against the encroach- 

 ment of the hard- wood trees. 



This is an illustration of but a single forest succession out 

 of a great many that forestry must recognize. For example, 

 in Oregon and Washington, where the conifer forests are so 

 conspicuous, they are the climax type, and there is no danger 

 of an invasion by hardwood trees. The conifers of that region 



