SILVICULTURAL CHARACTERISTICS 43 



The aspens are cold-enduring trees. For their best develop- 

 ment they require deep, fresh or moist, but porous and well- 

 drained soils. Sandy loams mixed with decayed vegetable 

 matter are the best. However, they are often found on thin, 

 dry, sandy soils as well as in poorly drained situations. 



The intolerance of shade shown by aspens, and its effect upon 

 the life history of aspen stands is the most important feature 

 bearing upon the relation of these species with other trees. 

 Throughout their life history the poplars endure less shade than 

 any of their companions. Unless the poplar has full light from 

 the beginning it is soon killed out by its more tolerant neighbors. 

 In this way aspen stands which may be nearly pure during youth 

 gradually give way to longer-lived and more shade-enduring 

 species, and only rarely succeed themselves. 



Poplar is commonly known as a rapid growing tree and it is 

 true that as a rule it grows faster than spruce, or fir or even paper 

 birch during the first twenty or thirty years. It is short-lived, 

 however, and usually infested by a fungus, Fames igniarius, by 

 the time it is forty, and begins to die at the top. The bark is 

 thin and the tree is damaged easily by fire. The average maxi- 

 mum size attained by poplar in the northeast is from sixty to 

 ninety feet in height and from eighteen to twenty inches in diam- 

 eter. Sound trees over one hundred years old are seldom found. 



As among all poplars and willows the staminate and pistillate 

 flowers of the aspens are borne on separate trees, except in rare 

 instances. The trees blossom and the seed falls in early summer. 

 Thrifty trees begin to bear seed when only twenty years old. 

 Although a great quantity of seed is produced a large proportion 

 of it is abortive, and unless it falls on mineral soil, on recently 

 burned over or cleared land or on other open spots not covered 

 with vegetation or leaves, it has little chance of developing. 

 This is why the aspen is so typical of burned areas. Besides the 

 reproduction from seed this tree is prolific of sprouts or root 

 suckers. Following fires in a poplar stand, and especially after 

 lumbering, a large proportion of the next generation of poplar is 

 from root suckers. 



