The history of fire between 1850 and 1977 in a portion of the
Willamette National Forest in-the central Western Cascades of Oregon was
documented using historical sources. Three types of records were
available: (1) records and writings not primarily concerned with fire
but yielding information about fire in context with human activities,
(2) descriptive accounts of fires prior to 1910, and (3) statistical
reports generated by the U.S. Forest Service from 1910 to the present.
Corresponding to each type of record, this study was divided into three
time periods: pre-1850, 1850-1909, and 1910-1977.
Information about the pre-1850 period was drawn from reconstructions
of aboriginal forest use by anthropologists, archaeologists, and
enthnographers. Although four groups of aboriginal people inhabited
areas within or adjacent to the study area, evidence is lacking for
intentional Indian burning in the central Western Cascades. Unintentional
burning from untended or abandoned campfires is probable.
Coupled with naturally occurring lightning-caused fires, these fires were ample ignition to maintain an age class of 125 years or older in
the forests of the central Western Cascades.
Information about fires occurring between 1850 and 1909 came from a
variety of historic sources. All chronicled fires were attributed to
man. Many man-caused fires were related to specific human activities,
including road building, sheep grazing, and camping. As human use
increased, the numbers of fires increased. Conflicts in use occurred
because of the threat of fire. Some activities, such as mining and
railroading, were not causes of fire in the central Western Cascades.
Lightning was not regarded as a cause of forest fires until after 1900.
Fire records for the period from 1910 to 1977 were generated by the
U.S. Forest Service. These records exist in various forms including
fire maps, summary tables, and individual fire reports. Almost 60
percent of all recorded fires from 1910 to 1977 were lightning caused.
While lightning ignited more fires, they were usually small and occurred
in mid-summer. Man-caused fires although fewer, were larger and occurred
throughout the fire season. An increase in the number of fires is
paralleled by an increase in forest use.
Two maps were constructed to illustrate the spatial distribution of
man-caused and lightning-caused fires. Lightning-caused fires appear to
be unevenly distributed over the landscape. Three areas exhibit a low
incidence of lightning-caused fires. Lightning fires occur at higher
elevations, where fuel accumulations are less, and tend to remain small.
Man-caused fires exhibit a definite pattern corresponding with land-use.
These fires tend to follow major transportation routes which are generally
at lower elevations. Man-caused fires, ignited at lower elevations,
have more chance to spread and become large fires.