244 ILLINOIS ACADEMY OF SCIENCE 



tbough the steps in tlie succession may be almost infi- 

 nitely slow. 



Among the most striking examples of edaphic or tem- 

 porary^ climax communities are the pine barrens of New 

 Jersey so well described by Taylor (3) and by Harsh- 

 berger (4), and the similar forests of scrub pine in 

 Michigan spoken of as "the plains" by Spalding (5) 

 and others. 



In New Jersey the area is within a region capable 

 of supporting a highly mesophytic forest in which chest- 

 nut, beech, maple and certain oaks are conspicuous. 

 Further, the sandy plains have been continuously out of 

 water for long ages, and are occupied by a plant com- 

 munity that gives evidence of being an '^old climax 

 condition infinitely more ancient than anything in the 

 surrounding area"; nevertheless this vegetation is far 

 below the climax of the region in mesophytism and in 

 comparison with it is to be classed as a primitive com- 

 munity. 



The vegetation of the sand plains of Michigan is simi- 

 lar to that of New Jersey. The principal tree of the 

 former, Piniis Banksiana, closely resembles in habit and 

 ecological relations the P. rigida which dominates the 

 latter, while the associated forms in each instance are 

 decidedly xerophytic, and very similar both floristically 

 and ecologically as may be seen by comparing the de- 

 scriptions of Taylor (3) and Grates (6). The Michigan 

 **pine barrens" are in a region where the climax forest 

 is characterized b}^ the dominance of beech, maple and 

 hemlock. 



Many different causes have been given for the perma- 

 nency of this primitive type of forest over the Michigan 

 sand plains, but such attempted explanations have 

 usually emphasized the character of the soil, its lack of 

 fertility, its poor water supply, and its deficiency in 

 humus or in essential mineral constituents. Harper (7) 

 asserts with some plausibility that the difficulty is that 

 the sandy soils leach freely and hence prevent the ac- 

 cumulation of any considerable amount of plant food 

 material. Whatever mav be the cause, the fact of the 



