94 THE BOOK OF FORESTRY 
ous, for while they consume the seed which has fallen and 
the little seedlings and may even kill some of the thin- 
barked’ saplings, they do not as a rule kill merchant- 
able timber. All of their results, however, are not visible 
immediately. Many a woodlot which has been swept by 
a severe ground fire may, four or five years later ex- 
hibit a very large number of trees affected with fungus 
diseases just above the ground. The trees really were 
damaged at the time of the fire but did not show it 
until later. Even though the trees may not be severely 
damaged the fire consumes the litter and leaf mold which 
should have enriched the soil and as a consequence 
growth will be seriously checked. On cutting down a 
tree the scars of an old fire may be seen towards the 
eenter of the tree and it is quite common to note that 
the annual growth rings have diminished in width after 
the fire, owing to the burning up of the food supply 
stored up in the humus. 
Surface fires are most common in the spring and fall 
and if the ground beneath is damp only the loose leaves 
on top will be consumed. In the regions where the 
long winters and short cool summers cause a thick 
accumulation of leaf mold or duff, this layer may take 
fire and the ground fire thus started may assume serious 
proportions. In such eases it may smolder along beneath 
the surface of the peaty layer, burning off the roots of 
the trees until the first strong wind will pile them up 
like jackstraws. If the duff is particularly thick a 
ground fire may smolder for months. 
A crown fire is a calamity hard to appreciate, and 
to see or hear one is an experience never to be for- 
gotten. Crown fires occur only during extremely dry 
seasons and in dense coniferous stands where the trees 
are very close together. The start of a crown fire occurs 
