Regional synchroneity in fire regimes of western Oregon and Washington, USA

For much of the world's forested area,,the history of fire has significant implications for understanding forest dynamics over stand to regional scales. We analyzed temporal patterns of area burned at 25-year intervals over a 600-year period, using 10 tree-ring-based fire history studies located west of the crest of the Cascade Range in the Pacific Northwest (PNW), USA, and related them to periods of possible influences of humans, climate, and stand development processes. An early period of widespread fire from the 1400s to ca. 1650 was followed by a period of reduced area burned from ca. 1650 to ca. 1800, possibly associated with cool climatic conditions. Fires were again widespread from ca: 1801 to ca. 1925, associated with European exploration and settlement and warm conditions. Fire suppression began ca. 1911, but appears to have been most effective in limiting the amount of area burned since ca. 1950. Anthropogenic change, climate, and the degree of stand/fuel development appear to have interacted in their influence upon temporal variation in fire regimes. Patterns of temporal variation in area burned were similar among the 10 studies, suggesting a regionally synchronous response. The roughly synchronous nature of fire in the region has important implications for our understanding of landscape dynamics under pre-settlement conditions. Forest landscapes of the Pacific Northwest may have exhibited high spatio-temporal variability even when large areas are considered. Major shifts in the landscape age class distribution were likely associated with episodic, high-severity disturbance events. Over certain time intervals in the past, particular seral stages of forest were either dominant across the region, or relatively scarce. (C) 2002 Elsevier Science B.V. All rights reserved.