| Long-term fire-history reconstructions are based on analyses of charcoal in lake sediments. Charcoal accumulation rates (CHAR) are typically decomposed into “peaks”, that describe local fire-frequency, nd “background” trends that represent changes in regional fires and fuels. A meta-analysis of fifteen sites in the northwestern U.S. was undertaken to examine these trends at a larger spatial scale. Comparisons between background CHAR and pollen, fire-frequency, and topographic data were made to help explain the patterns. Analysis revealed a widespread increase in background CHAR since the late-glacial and an abrupt decline 1500 cal years ago. Comparisons between background CHAR and pollen data indicate that these trends were a result of postglacial forest development and increased fuel levels. Similar trends in background CHAR and charcoal peak frequency among sites suggest that variations in vegetation and climate caused regionally coherent changes in fire, and differences in background CHAR levels were related to local-scale topographic variations. |
