170 COMMISSION OF CONSERVATION
fire scars eight years old. By counting the annual rings of the wood covering the fire scars on the few mature trees still standing, it would be found that they had been severely injured by fire approximately 8, 16 and 25 years ago. Therefore, the area would be classed as having been burned three times. Severe fires usually burn off the brush and duff down to the mineral soil. These areas form ideal germinating beds for poplar, which requires plenty of light, and whose seeds are easily and widely distributed and germinate quickly. The poplar grows rapidly for the first few years, and the young seedlings soon cover the ground. The seedlings from the seed crops of the few succeeding years are too much shaded to compete successfully with those already on the ground. The result is a pure or a nearly pure stand of even-aged trees. Fire is practically the only agent that can make the proper conditions for the development of such stands. Clean cutting without the usual subsequent fire might bring about pure stands in restricted patches, but, taking the area as a whole, it would be found that the poplar would not come among the brush piles until they decayed. The result would be " patchy " stands of different ages. In any case, the presence or absence of fire scars on the escaped mature trees would furnish the necessary corroborative evidence that we are dealing with burned areas.
One is, then, not dependent upon hearsay or tradition in determining the number of times an area has been severely burned. Every severe fire leaves its record burned into the trees not actually killed, and stamps its impress upon the succeeding generation of trees.
Many The designation number of times burned, in these dis-
Smaller cussions and on the accompanying map, means that
Fires the greater portion of the area so designated has been severely burned the number of times indicated; that is, burned sufficiently to scar the sfanding trees and to kill off portions of the young growth periodically, so that stands of different age classes have resulted where more than once burned. It will be seen that this method of designation takes no account of the ground fires, which did not develop sufficient heat to burn into the wood of the trees or to kill the young trees in large quantities. Fires of this kind are frequent in the dry periods of the last week of April and the first week of May, when the leafage is not sufficiently developed to feed the flames and when only the upper layer of the vegetable debris on the ground is dry enough to burn. It is evident that fires of this kind are very destructive to the tender seedlings of pine and, on the other hand, that they stimulate the reproduction of birch and poplar, both because the fires make a clean seed-bed and because the birch and poplar sprout vigorously.