250 G. A. PEARSON 



The effect of fire has been aided by competition from grasses and 

 in recent times by heavy grazing. Since aspen is extremely 

 intolerant of shade, the prior establishment of other vegetation 

 may preclude its reproduction. 



The propagation of aspen at the present time seems to take 

 place mainly by means of root suckers. Young aspens originating 

 from seed are of rare occurrence. Undoubtedly reproduction 

 from seed takes place under proper conditions ; otherwise the wide 

 range of the species and its rapid occupation of large burns could 

 not be accounted for. But extension by means of root suckers is 

 far more effective than is commonly supposed. It is quite possible 

 that many of the largest aspen stands on burns owe their existence 

 mainly to the activity of roots remaining alive after the coniferous 

 forest was destroyed by fire. Despite their intolerance of shade, 

 occasional aspens, probably remnants of a once thrifty stand, 

 are scattered through many of the densest spruce forests. The 

 tall, slender, usually crooked stems and scanty crowns of these 

 individuals bear witness of their losing struggle for light. But if 

 a fire should destro}^ the coniferous trees, the surviving aspen roots 

 form the nuclei of numerous thickets which spread from year to 

 year and tend to merge into one another. Sometimes the aspen 

 may be entirely killed by its competitors before the fire occurs, or, 

 if the fire is severe, it may destroy all the aspen roots. ^ Under 

 such conditions the only way in which aspen can take possession 

 of the land is through seed. 



The failure of conifers to establish themselves satisfactorily on 

 extensive burned-over areas of the national domain gives rise to 

 the need for artificial reforestation, a task which is being under- 

 taken by the United States Forest Service. A necessary prelimi- 

 nary step to so extensive an operation is a thorough investigation 

 to determine under what conditions and by what means artificial 

 reforestation can be most economically accomplished. 



The fact that the most valuable of the high altitude trees, par- 

 ticularly Douglas fir and Engelmann spruce, apparently reproduce 

 themselves best under a cover of aspen immediately suggests that 



' Weigle, W. G. , and Frothingham, E. H., The Aspens, their Growth and Manage- 

 ment. U. S. Fore-st Service Bull. 93, p. 18. 



