Fire has been a critical influence on forest dynamics over much of western North America, and knowledge of historical fire regimes provides a valuable reference point for guiding ecosystem management. Spatial and temporal variations in historical (1550–1997) fire frequency were quantified for a 145-km2 area straddling the McKenzie River in the central western Cascades of Oregon. Fire-scar and tree-origin years estimated from cut stumps in 63 clear-cut sites were used to approximately date fires. The estimated natural fire rotation was 162 years for the presettlement period (1550–1849). Natural fire rotation varied considerably over the period of record, ranging from 40 years for the Euro-American settlement period (1850–1924) to 504 years for the recent (1925–1997) fire-suppression period. Such temporal variation in fire regime may be attributed to a combination of climatic and anthropogenic influences. The study area also experienced 2 periods of widespread fire recorded at a majority of sample sites: one in the mid-1500s and the other from 1850 to 1925. Historical fire frequency has also varied spatially over at least 2 distinct scales. At the slope-facet scale, fire frequency was greatest on the generally south-facing slope to the north of the McKenzie River. At the finer scale of individual 4-ha sites, local topographic influences varied according to a site's broad geographical context north or south of the river. Results suggest that meaningful fire-regime characterization may require information derived from multiple spatial scales.
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Vol. 69 • No. 2