1905] WHITFORD—FORESTS OF FLATHEAD VALLEY 295 
can be seen that fires will tend to reduce the humus content of the 
soil. This is of extreme importance, for that which would otherwise 
add to the richness of the soil and increase its water-holding capacity 
is destroyed. Especially is it of importance in those regions that 
border on the prairie. There is evidence of many such surface fires 
in the open woods around Nigger Prairie, and it is very probable 
that these fires have played an important réle in keeping the prairie 
vegetation from being encroached upon by the forests that surround 
it. Even in the mesophytic conditions, fires influence the capacity 
of the soil to reforest itself quickly, by partially or totally destroying 
the humus. However, with the reclothing of the burned area, the 
floor of the new forest will gradually resume its normal condition. 
From the above it will be seen that forest fires play an important 
part in determining the composition of the forest. That forest fires 
prevailed in this region before the advent of civilized man is a logical 
inference. In the lodgepole pine forest in the Swan River there are 
unmistakable signs of fires before the present forest, which is now 
about one hundred years old, was started. How these fires started 
can only be conjectured, and it is not within the province of this paper 
to discuss their origin. It is also very evident that the fires are more 
numerous since the settling of the country by civilized man than 
ore. 
- SUMMARY. 
_1. Fires play an important part in determining the present compo- 
sition of the forest. 
2. The lodgepole pine is the “fire tree” of the region. 
~ 3- It is favored after fires principally because it has the capacity 
to produce seeds early in its life. 
4. Many complex conditions of growth are introduced after fire. 
The species that have seed-bearing trees near the burn will generally 
be represented in the new forest. e 
5- Repeated burnings at intervals of ten to thirty years will 
establish a lodgepole pine forest where formerly there existed a normal 
mesophytic forest. 
6. Repeated burnings at intervals of five years or less will destroy 
all forest growth. 
