HERMAN H. CHAPMAN 29 



of survival of the seedling is increased by its tolerance, and 

 later in life with increasing need of light, the increased 

 size gives it the chance to secure this light. Tolerance is 

 also increased by favorable sites. If a species is growing 

 in a climate whose temperature is most favorable to it, 

 the vigor of growth is at its maximum and it needs less 

 light than it does when growing at the extreme limit of its 

 range. The relative tolerance of two species, therefore, 

 may not be the same in different regions, for a tree is al- 

 ways more vigorous when near the center of its range. In 

 spite of these differences, tolerance is so marked a charac- 

 teristic of different species that the trees in any region may 

 be roughly classified in order of their needs for light. 



A general list, given by Dr. B. E. Fernow, for northern 

 trees, will illustrate such classification. The most intol- 

 lerant trees, or those needing the most light are given first, 

 and the trees grouped together are of nearly equal degrees 

 of tolerance. 



Aspen 

 Cottonwood 

 Black Locust 

 Honey Locust 



Black Oak 

 Pitch Pine 



Soft Maple 

 White Pine 

 Hickory 

 White Oak 



r Sugar Maple 

 Beech 

 Balsam Mr 

 Spruce 

 Hemlock 



Norway Pine 



Tulip Poplar 



Elm 



Basswood 



White Birch 



Black Cherry 



Walnut 



Chestnut 



This is a fairly good list; since it does not attempt to 

 state which of two similar species is the most tolerant. 



