i 9 i 4 ] ROBERTS— PLANT SUCCESSIONS OF HOLYOKE RANGE 435 



There is little bare rock exposed except on the cliff faces and at 

 the edges of the highest peaks; there weathering is playing an 

 active part. Small and large flakes of the trap rock are being split 

 from the face. A great many of them pile up at the top of the 

 talus slope and furnish splendid agents for catching the finer 

 material which is washed down. 



The vegetation is playing an active part in changing the 

 physiographic features of the region. 



Classification of successions 



determined 



original xerophytic and hydrophytic habitats, that I have classified 



terms 



follows : 



Xerarch successions : (i) trap slope successions; ( 



successions; (3) 



II. Hydrarch successions: (1) ravine successions; (2) brook 

 successions. 



All the region except the brooks has passed through several of 

 the successions leading to the climax forest, and a small area is 

 now in the beech-maple climax, which is the culminating stage of 

 the region, while a little to the west of the range the hemlock forms 

 the climax. There is, however, in this region some indication of 

 the hemlock coming in as a climax type. 



It is doubtful if there is any climax representing that of the 

 so-called primary succession, which might well be called the initial 

 succession. The region represents a third or fourth attempt to 

 develop a climax forest, as do most of the New England forest areas. 

 These successions have been called secondary successions, but 

 might better be called repetitive successions, because the defores- 

 tation causes the area to revert to an aspect which is a combination 

 of a former succession with the successions which ordinarily follow 

 it. The term " secondary " does not carry with it the idea of more 

 than one attempt at repetition, while "repetitive" indicates no 

 limit in the number of attempts. 



Mount Tom has been a state reservation for 10 years, and since 

 then has been free from the retarding and retrogressing factor, man. 



