Question

the light burners proposed to \control\ the destructiveness of the deliberate firing by burning the woods in the spring or fall when sufficiently moist to prevent the fire from seriously injuring either old timber or young trees. a careful study of the area... shows that such control amounts to little or nothing. the light burners ignore.... the rapidity with which... sunlight in warm weather dries up the litter in the pine woods. a south slope will be so dry as to make any fire exceedingly hot and destructive before a north slope will burn at all. areas which will burn but lightly and irregularly early in the morning will flare up and consume in the most approved fashion by mid - afternoon. the moisture following light spring or fall rains often disappears so rapidly that the period of \safe\ burning is a matter of hours, not of days. actually to burn the western pineries, as the advocates of this theory propose to burn them, would, if it could be done at all, entail a cost for effective control many times greater than the cost of an efficient

Explanation:

The text mentions that the moisture following light spring or fall rains disappears rapidly, and the period of "safe" burning is short (hours, not days). It also states that the light burners ignore the rapidity with which sunlight in warm weather dries up the litter in the pine woods. This shows that the weather (including factors like moisture - drying sunlight and the rapid disappearance of post - rain moisture) changes too quickly to predict.

Answer:

the weather