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Fire and Climatic Variability in the Inland Pacific Northwest: Integrating Science and Management
McKenzie, D., A.E. Hessl, D.L. Peterson, J.K. Agee, J.F. Lehmkuhl, L-K.B. Kellogg, and J. Kernan. 2004. Fire and Climatic Variability in the Inland Pacific Northwest: Integrating Science and Management. Final report to the Joint Fire Science Program on Project #01-1-6-01, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 44 pp.
We proposed and developed a multi-scale analysis of the relationships between climate and topography and spatio-temporal patterns in historical fire regimes in the inland Pacific Northwest, using existing fire history data from six watersheds on the Okanogan-Wenatchee and Colville National Forests. We investigated current year, lagged, and low frequency relationships between composite fire histories and Palmer Drought Severity Index (PDSI), Pacific Decadal Oscillation (PDO), and the Southern Oscillation Index (SOI) using superposed epoch analysis and cross-spectral analysis. We identified smaller scale controls on fire exerted by fuel limitations by comparing patterns of fire hazard over time on simulated landscapes without controls to landscapes in the six watersheds. We used spatial autocorrelation, geostatistics, and multivariate methods to quantify the spatial structures of fire regimes and how they depended on local topography. We documented clear differences in fire regimes between the historical period (ca. 1650-1900) and the period after initiation of fire suppression in the region (ca.1900). We developed a unique geo-spatial database that takes advantage of both the spatially explicit nature of the fire-history data and new paradigms in geographic information science.
Major findings include:
-- The El Niño/Southern Oscillation (ENSO) was only a weak driver of fire occurrence in the past three centuries, but fires tended to occur during dry summers and during the positive phase of the PDO. In the Pacific Northwest, attention should be paid to summer moisture conditions the year of the fire. Long-term fire planning using the PDO may be possible in the Pacific Northwest, potentially allowing decadal-scale management of fire regimes and vegetation dynamics.
-- The relationship between drought and fire occurrence was disrupted during the 20th century as a result of land use changes.
-- At small scales (20 ha or less), likelihood of fire clearly increased over time on fire-history sites that experienced short fire-return intervals, suggesting that fuels build-up was the primary local control on fire.
-- In watersheds with longer fire-return intervals, this pattern did not hold. Fire occurrence displayed spatially heterogeneous temporal patterns in watersheds in which the sample area was dissected by topographic boundaries, whereas this was not the case where topography was gentle or where all recorder trees were in a single basin. Thus, spatial variation in historical fire regimes was clearly a function of topographic structure.
In some of the watersheds, fires virtually disappeared in the 20th century; in all watersheds, 20th century fire regimes departed from their historical patterns, suggesting that to a large degree human influences have disrupted historical controls. This process may not be reversible. Given projected climatic changes and documented relationships between fire and climate, reference conditions from pre-1900 may not be achievable.
The GIS database is being placed on a dedicated web server, on CD-ROMs, making it available not only to fire managers in eastern Washington, but also to those around the country and the world for whom this extraordinary spatially explicit record of fire would be of use. It will also be linked to the Paleofire Database (http://www.ngdc.noaa.gov/paleo/impd/paleofire.html). Project scientists based in Seattle (McKenzie, Kellogg) will provide ongoing support to local users (Okanogan-Wenatchee and Colville national forests) of the database.