TIMBER; FORESTRY 113 
group oaks, elms, and ashes; in another, oaks and _hicko- 
ries; in another, beeches and maples (fig. 95). Along the 
fertile river bottoms of the Middle West one may often find 
a combination of sycamores, oaks, ashes, black walnuts, elms, 
and hackberries. 
106. Tolerant and intolerant trees. A tree which can endure 
a good deal of shade is said to be tolerant. Examples of this 
are the hemlock and red spruce, among conifers, and the 
beech and maple, among hard 
woods. Trees which require 
much light are said to be zntol- 
erant. Examples are the white 
pine and the larch, among 
conifers, and the oaks, hicko- 
ries, and chestnuts, among 
hard woods. As a rule, seed- 
lings require far less light 
to begin life than is needed 
to enable the mature tree to 
reach its maximum size. So 
it often happens that seedling 
trees may survive for years on 
the forest floor, making but 
little growth until the decay 
and fall of overshadowing trees, 
their destruction by wind, or 
their removal by the lumber- 
man enables the seedling to grow rapidly into a large tree. 
The relative tolerance of trees is an important topic in prac- 
tical forestry, since the succession of forest growths often 
depends largely upon this factor. White-pine seedlings could 
not be made to grow under a good stand of pine or hemlock 
timber, but young hemlocks or red spruces would succeed 
there. On the other hand, white-pine seedlings can grow in 
an aspen forest, and white oak and maple seedlings can grow 
in an oak-maple forest. 
Fie. 95. Primeval deciduous mixed 
forest of maple and beech 
