Fire History in the Ponderosa Pine/Douglas-fir Forests on the East Slope of the Washington Cascades

Document Type

Article

Journal/Book Title/Conference

Forest Ecology and Management

Publication Date

2000

Issue

1-3

Volume

129

Publisher

Elsevier

First Page

207

Last Page

225

Abstract

We collected 490 and 233 fire scars on two ponderosa pine (Pinus ponderosa)/Douglas-fir (Pseudotsuga menziesii) dominated landscapes on the east slope of the Washington Cascades that contained a record of 3901 and 2309 cross-dated fire events. During the pre-settlement period (1700/1750–1860), the Weibull median fire-free interval (WMFFI) and the mean fire-free interval (MFFI) were 6.6–7 years at both sites. The MFFI during the settlement period (1860–1910) varied within 3 years of the pre-settlement value, but increased to 38 and 43 years for a truncated fire suppression period between 1910 and 1996. Increased variation in MFFI among aspect polygons suggests fire regimes have become more complex since Euro-settlement. In the pre-settlement period, an area equal to approximately 50–60% of the study areas burned every 6–7 years, an amount of fire disturbance apparently in balance with landscape and stand vegetation structure. Overlapping fires have created a complex mosaic of different fire histories on these forested landscapes. Mapped fire events from the 1700–1910 showed 134 and 157 separate fire history polygons (FHP) at the two sites. Fire disturbance rates and patterns are suggested as ecologically defensible reference points for landscape heterogeneity to reduce the potential for catastrophic fires and to establish vegetation disturbance management guidelines.

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