HOW THE FOREST IS GUARDED 93 
shown that fires caused by hghtning or set by Indian 
hunters to drive out game swept over the mountains 
again and again long before white men settled on the 
Atlantic Coast. In fact, the vast stretches of lodgepole 
pine in northern Colorado are believed to be the result 
of these early fires, as this species finds ideal conditions 
for germination and growth after the forest soil has 
been heavily burned. 
It is only within the past few years that an organized 
effort has been made to prevent and check forest fires. 
Formerly they were regarded as an act of Providence 
and the advancing flames were fought only when they 
approached a village. Otherwise the fires were gener- 
ally allowed to burn until the wind changed or a general 
rain made the forest too wet to burn. Within late years 
and largely as the result of fire-fighting experience 
by the foresters of the country, lumbermen have learned 
that forest fires are largely preventable, and under 
ordinary circumstances can be extinguished if attacked 
at once. As a consequence in addition to the fire- 
fighting force of patrolmen, forest guards, and look- 
out men, maintained by the National Forest Ser- 
vice and many of the States, protective associations are 
now being formed by lumbermen to reduce their fire 
risk. 
Forest fires may be divided into three classes: First, 
those that burn along the surface of the ground, called 
surface fires; second, those that burn in the duff or 
layer of vegetable mold on top of the mineral soil— 
ground fires; and third, the crown fire which burns 
from tree to tree with the head of the fire up in the 
treetops and the widespread wings trailing down upon 
the ground. 
Surface fires are the most common and least danger- 
