20 U. S. DEPARTMENT OF AGRICULTURE BULLETIN NO. 484. 



trol, make it impossible to disregard them if success is to be expected 

 in managing a stand in which they are present. 



The possession of these characteristics puts these 18 trees in a 

 separate class from the others, and the clear recognition of what the 

 characteristics are will greatly simplify our problem and seems to 

 justify the designation of these species as " controlling trees." Unless 

 exactly understood, this term may lead to confusion. Perhaps " por 

 tentially controlling trees " would more accurately describe what is 

 meant. 



Their mere presence in a stand does not necessarily make them con- 

 trolling. If one or more of these species is present in such numbers 

 as to be the leading species, no confusion can arise, for their mere 

 numbers make them a controlling factor, and their silvical character- 

 istics reenforce and strengthen their power of control. When less 

 numerous, the question whether or not a particular species is one of 

 the controlling factors depends upon a careful consideration of how 

 many trees there- are of each species and of the effect likely to be 

 produced upon the stand by the other controlling factors in that 

 stand. 



The chief silvical characteristics which under certain conditions 

 majr make these species controlling factors in management are: 



(1) Adaptability to certain sites; 



(2) Tolerance of shade; 



(3) Power of abundant reproduction by seed; 



(4) Power of abundant reproduction by sprouts or by root suckers ; 



(5) Rapid growth. 



Of the species possessing one or more of these silvical characteris- 

 tics, there are listed as controlling trees only those which are actually 

 found, in some stands in the white-pine region, in sufficient numbers 

 to become a controlling factor in those stands. What constitutes 

 sufficient numbers is, of course, a matter of opinion upon which in- 

 dividual foresters may differ. That of the present writer will appear 

 later in the suggestions for management of each of the stands now 

 under consideration. 



The list given below includes 18 species falling within the limita- 

 tions above described. They may fairly be called controlling trees of 

 the white-pine region. In a table which follows the list these species 

 are shown again, grouped under the silvical characteristics which de- 

 termined their inclusion in the list. This is followed by a brief state- 

 ment for each species of the conditions under which the potentially 

 controlling trees may become actual controlling factors in manage- 

 ment in individual stands in the white-pine region. 



In the suggestions for management which follow later all other 

 species are disregarded or are given only the most general consid- 

 eration. 



