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FOREST FIRES AND BRUSH DISPOSAL   165

would probably not exceed that in the past. This loss, however, has been augmented by freshly cut, unburned material.

It has been the general policy on the National forests and on some private holdings to burn all slash, but this slash has not always been burned at the right time. In order to prevent the insect broods which destroy standing timber from escaping, the slash must be burned before the brood escaped. Where these broods have escaped from public and private operations resulting in slash, small epidemics have started wherever the conditions were favourable. An instance of this is the Cox timber sale on the Plumas National Forest, where an epidemic, started from the cull logs and slash, killed a large percentage of the standing timber on the hillside above the mill the following year.

An epidemic has just appeared in the eastern Lassen National forest, along the right-of-way for the Fernley and Lassen branch of the Southern Pacific railway. This started in the logs and slash felled in clearing for construction. Unless controlled, .these epidemics increase from year to year and are often augmented by broods from other freshly cut material.

The infesting species is often different, due to different species of trees or parts of trees. Thus a cull log or top of yellow pine (Pinus ponderosa) breeds the western pine beetle (Dendroctonus brevicomis), the most destructive beetle to yellow pine on the Pacific coast. Tops and limbs breed another very destructive species, an engraver beetle (Ips confusus), killing tops of trees and young growth. No matter what the species of tree the slash resulted from, that slash breeds under ordinary circumstances the insect or insects destructive to standing timber. The annual loss from this cause alone far exceeds any cost incurred from the burning of the slash at the proper time. Therefore, the consideration of the burning or non-burning of brush must be taken up from a broad protection standpoint and not from the standpoint of fire risk or cost alone.


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