TOLERANCE OF FOREST TREES AND ITS RELATION TO 

 FOREST SUCCESSION ^. 



By George P. Burns 

 Vermont Agricultural Experiment Station 



It is with considerable reluctance that I appear before this body of 

 practical and experimental foresters to discuss briefly the problem of 

 tolerance of forest trees and its relation to forest succession. This is 

 especially true because the results of my own ecological work, both 

 that of observation in the forests and of experiments in nursery and 

 greenhouse, do not apparently assign to light the all-commanding posi- 

 tion with which it seems to be associated in the minds of many persons 

 engaged in the work of silviculture. The literature of this subject is 

 closely interwoven with the words "tolerance"' and "intolerance" and 

 an agreement as to the exact meaning of these words on the part of 

 all workers in this field is essential as a starting point for a clear 

 understanding of the problems in hand. 



Dr. Fernow says that the present theory of tolerance was first sys- 

 tematically developed by Heyer and published in 1852, and on this 

 work is built the whole philosophy of silvicultural methods. At the 

 time of its origin then it was based wholly on observation. It was 

 published 10 years before Roscoe-Bunsen published their important 

 work on Meteorologische Lichtmessungen, 20 years before the impor- 

 tant work of Wiesner began to appear, 51 years before the appearance 

 of Schimper's plant geography, and many years before forestry litera- 

 ture began to be illuminated by the writings of Zon, Clements, Bates, 

 Hofifman, etc. In fact all of the ecological work which is based on 

 exact research has appeared since that date. 



Dr. Fernow says that "Tolerance means to the professional for- 

 esters only a light relationship and nothing more." It is the intention 

 of the writer to attempt to analyze some of the literature to see 

 whether or not this idea is shared by all foresters. 



In accordance with the present theory trees are arranged according 

 to their so-called light requirement into a series beginning with the 



^ Delivered before the Society of American Foresters at its annual meeting in 

 New York, N. Y., January 14, H)20. 



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