[January BOTANICAL GAZETTE 50 



bracken seems to interfere little with this herbage, in fact may 

 protect it. They occupy a different level and seem comple- 

 mentary (22). 



The preceding types are alternative. Which enters depends 

 on soil conditions, topography, and seeds present. Aspen succeeds 

 best after fire and in higher dry ground. Pin cherry seeds are 

 bird-scattered (and fertile longer), thus being more apt to reach a 

 favorable place. The xerarch tree society is able to enter in many 

 cases where climax forest is sufficiently cleared, either with or with- 

 out intervention of treeless stages. The greater the degree and the 

 quicker the recurrence of interference, the more likely regressive 

 changes are to occur, its amount and the environment determining 

 whether the ensuing secondary state be repetitive or non-repetitive, 

 and, if the latter, whether it be thrown back to tree, shrub, or herb 

 stage (the farthest being the fireweed semi-desert), that is, the 

 degree of rejuvenation. 



Regeneration of the climax forest may be speedy, hardwood 

 saplings following a mixture of fireweed and thorn. This results in 

 a remarkable floristic mixture. Behind Bay View a nearly pure 

 stand of red maple has been formed after cut over. At Walloon 

 Lake the beech is apt to dominate in the regenerating climax forest. 

 In other places Acer spicatum and A. pennsylvanicum are impor- 

 tant. If the xerarch tree society takes charge of a district it may be 

 followed by yellow birch and elm (18) before the climax supervenes. 

 Grass turf may prevent tree entrance (11, 12), but it would appear 

 that milkweed and sumac, at least for dry upland, could replace it. 



Discussion 



The upland societies here studied show that most of the area 

 of this character was occupied before settlement by climax forest. 

 The forest itself (as any climax) is static in species but dynamic 

 as to individuals, so that the climax is not final but recurrent. 

 Five life ages may be singled out in this forest, each with its own 

 dimensions and ecological characters. Thus the sapling age shows 

 maximum increase in size for given decrease in number per unit 

 area, so that competition between trees of equal age is keenest 

 here. 



