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 charactertistics 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 “ po- 
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 
may 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 spr sith 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. 
