HERMAN H. CHAPMAN 27 



At the other extreme we find trees occupying soils so 

 dry that many species are killed by drought and cannot 

 grow in such places. On the dry, rocky ledges in eastern 

 states the red cedar finds its natural habitat, while on the 

 dry, deep sands of the Lake States the Jack pine has a clear 

 field against all competitors. Other species like Norway 

 pine and scarlet oak, come in on soils too dry for white pine 

 which, in turn, needs less moisture than hard maple. Spe- 

 cies which grow only in dry soils are almost never found 

 in swamps. Norway pine, for instance, will not grow where 

 water stands in the soil. They are affected by rot even 

 when they grow in moist ground. It is evident, as in the 

 case of the true swamp species, that they are so accus- 

 tomed to their habitat that a permanent change in the 

 water content does not agree with them. They can no more 

 stand excessive moisture than swamp trees can stand dry 

 conditions. *But on the best sites, well-drained soils with 

 a good supply of moisture, most of these hardy trees will 

 do much better than on their usual site and grow faster 

 and larger. 



The only reason that they are not found on better soils 

 is that other species are stronger and crowd them off, leav- 

 ing them the alternative of dying or taking the poorer sites. 



Strong species, then, are those that can capture the most 

 desirable soils and secure for themselves the best and most 

 uniform supply of soil moisture. These species are usually 

 found to be hardwoods, such as the hard maple, chestnut, 

 white oaks and hickories. 



The Struggle for Light as Affecting Competition of Spe- 

 cies. But in what does the strength of such species con- 

 sist? 



The ability to capture soil moisture simply means that 

 the tree from some quality or other, is able to grow faster 

 than others or survive its competitors. Where there is 

 enough moisture for all, it is not moisture but other factors 



