444 A TEXTBOOK OF GENERAL BOTANY 
is due in part to the fact that in the coniferous forests there is no 
season during which the undergrowth is not shaded by the foliage 
of the trees, and in part to the fact that a carpet of slowly decay- 
ing, dry, resinous leaves hinders the establishment of seedlings. 
Fi1c.498. Interior of coniferous forest, Taku 
Inlet, Alaska 
The trees are Picea sitchensis and Tsuga 
heterophylla 

Vast areas in the north 
temperate zone are COv- 
ered by coniferous forests 
(Figs. 477, 495, 498). 
These are well devel- 
oped in Europe, Siberia, 
and Canada, and in the 
northern, western, and 
southeastern portions of 
the United States. The 
northern boundary coin- 
cides everywhere with 
the limit of tree growth. 
The largest stands of 
timber in the world are 
found in the coniferous 
forests which appear on 
the western coast of the 
United States. 
Tundra. From_ the 
standpoint of plant geog- 
raphy the boundary of 
the arctic region may be 
considered as the place 
where the last stunted 
trees disappear. This 
may be on either side of 
the arctic circle. North of this limit, where ice does not cover the 
ground tundra dominates the arctic region. The growth is usu- 
ally open and always dwarf, and mosses and lichens predomi- 
nate. In favored situations there may be patches of meadows 
or dwarfed shrubs. 
