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A 1416-year reconstruction of annual, multidecadal, and centennial variability in area burned for ponderosa pine forests of the southern Colorado Plateau region, Southwest USA

Fire history reconstructions from fire scars in tree rings have been valuable for assessing fire regime changes and their climatic controls. It has been asserted, however, that these two- to four-century long records from the western USA are unrepresentative of longer periods of the Holocene and are of limited use for understanding current or future fire regimes. The Medieval Climate Anomaly (800–1300 ce) is often suggested as a better analog for future Southwestern US climates but is beyond the chronological range of most fire-scar studies in this region. To evaluate fire regime changes over the past millennium, we build on centennial-length fire–climate studies to generate a 1416 year long reconstruction of fire activity in ponderosa pine forests of the Southern Colorado Plateau region of Arizona and New Mexico. We used a split-period calibration and verification protocol to test the reliability of a multiple regression model using annual and antecedent precipitation (reconstructed from tree-ring width chronologies) to predict the percentage of fire-scar localities (i.e. sites, N=45) that recorded extensive fires within those sites (>25% of recorder trees scarred) each year between 1700 and 1899 ce. The model explains approximately 50% of the variation in annual fire activity. Applying the model to the entire precipitation reconstruction provides a proxy for annual area burned since 572 ce. There are no statistically significant differences between the period available for fire-scar study (1600 ce–present) and the Medieval Climate Anomaly (800–1300 ce) in terms of predicted annual area burned or the frequencies of regional fire years. Multidecadal and centennial variation in the frequencies of regional fire years, however, does indicate reduced surface fire frequencies from approximately 700–800 ce and 1360–1455ce. We hypothesize that these were periods when some forests were vulnerable to altered canopy structure, accumulated fuels, and increased fire severity.