CHAPTER X 



THE cli:max forest and its predecessor, the 



OAK-HICKORY TYPE 



» 



HE succession of stages traced in the 

 preceding chapter lead on to the chmax 

 forest. On the dunes cottonwoods and 

 their confreres are replaced by the pine 

 association. This is in turn invaded 

 and ultimately displaced by the black 

 oak society. After many generations 

 of accumulated forest debris, the soil 

 becomes sufficiently rich in vegetable mold under such trees to 

 support red oaks, then white oaks, and the mixed oak succession 

 follows with its associated shrubs and herbs. Then hickories 

 appear with the oak, and finally under most conditions maples 

 and beeches displace all other trees. The interdunal pond and 

 the filling lake, if they lead on to a forest at all, go through a 

 similar succession and end in the same climax forest, except 

 possibly in the case of the sphagnum bog. 



Probably not one but many factors are involved in this suc- 

 cession. The increasing quantity of decomposing vegetable 

 matter in the soil not only supplies more and more plant food but 

 it also increases very greatly the power of the soil to retain mois- 

 ture. The numerous penetrating rootlets of the dense forest 

 growth, the burrows of earthworms and other animals not found 

 in the earlier stages increase the porosity of the soil. Increasing 

 shade prevents rapid evaporation, maintains a lower temperature 

 by shutting out the sun 's rays, reduces wind action, and lessens 

 very greatly the light intensity. In the beech-maple forest 

 the photographic exposure meter indicates a light intensity of 

 only one-tenth to one-twentieth that of the surrounding open 



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