An overview of fire in the Sierra Nevada

Fire, ignited by lightning and Native Americans, was common in the
Sierra Nevada prior to 20th century suppression efforts. Presettlement
fire return intervals were generally less than 20 years throughout a
broad zone extending from the foothills through the mixed conifer
forests. In the 20th century, the areal extent of fire was greatly reduced.
This reduction in fire activity, coupled with the selective harvest
of many large pines, produced forests which today are denser,
with generally smaller trees, and have higher proportions of white fir
and incense cedar than were present historically. These changes
have almost certainly increased the levels of fuel, both on the forest
floor and “ladder fuels”—small trees and brush which carry the fire
into the forest canopy. Increases in fuel, coupled with efficient suppression
of low and moderate intensity fires, has led to an increase
in general fire severity.

We suggest extensive modification of forest structure will be necessary
to minimize severe fires in the future. In high-risk areas, landscapes
should be modified both to reduce fire severity and to increase
suppression effectiveness. We recommend thinning and underburning
to reduce fire-related tree mortality coupled with strategically placed
defensible fuel profile zones (DFPZs). DFPZs are areas in which
forest structure and fuels have been modified to reduce flame length
and “spotting”, allowing effective suppression.

This chapter is an overview of work by the fire-subgroup of the
Sierra Nevada Ecosystem Project. Details concerning these findings
are found in Skinner and Chang 1996; Chang 1996; Husari and
McKelvey 1996; McKelvey and Busse 1996; Erman and Jones 1996;
van Wagtendonk 1996; and Weatherspoon 1996.