The Spell of the Rockies by Enos A. Mills

The big trees of California are never attacked by insects. This immunity is extraordinary and may be the chief characteristic that enables these noble trees to live so long. Unfortunately it is not shared by other species. The American forests are infested with thousands of species of injurious and destructive insects. These insects, like the forest fires, annually kill numerous forest areas, and in addition leave millions of deformed and sickly trees scattered through the living forest to impair and imperil it. After some general tree studies which have occupied odd times for years and extended through the groves and forests of every State and Territory in the Union, the conclusion has been forced upon me that the forests are more widely wasted by insects than by fire.

Some of Nature's strange ways are exhibited in the interrelation of insects and fires in tree-killing. It is common for the attack of one of these tree-enemies to open the way for the depredations of the other. The trees that insects kill quickly become dry and inflammable and ready kindling for the forest fire. On the other hand, the injuries that green trees often receive from forest fires render them most susceptible to the attacks of insects.