Data from: New methods provide a 300–year perspective on modern area burned in two wilderness areas of the southwest United States

Climate change and increased fuels from fire exclusion drive recent
increases in area burned and fire severity in dry conifer forests of the
western United States. Recent increases in area burned are occurring
against the backdrop of a large fire deficit caused by over a century of
fire exclusion. A key land management question is whether fire regimes can
be restored – i.e., can the fire deficit be paid off? Accurate estimates
of historical area burned prior to fire exclusion (circa 1900) are
difficult to derive and have rarely been calibrated or validated against
modern fires, leaving their accuracy uncertain. In this study, we applied
multiple time-series methods to tree-ring fire-scar data for the first
time, including a multi-model ensemble, time-varying predictor subset
calibration, and multiple measures of model uncertainty and validation. We
focused on two southwestern U.S. wilderness areas – Saguaro National Park
(SAGU) and the Gila Wilderness (GILA) – that have abundant and
well-documented modern fires due to decades of active fire restoration,
allowing us to test whether the area burned has been restored to
historical levels. Our ensemble of ten fire-scar models accurately
estimated area burned by modern fires with no consistent biases. While
individual models did not differ significantly from mapped fires, the
ensemble solution reduced overall bias and uncertainty. Each member model
has distinct strengths that make them suitable for specific applications
(e.g., the synchrony model is easily applied, and Thiessen polygons
provide spatially explicit estimates). The accurate reconstruction of the
modern area burned from relatively sparse fire scar data at GILA suggests
that dense grids are not necessary for accurate reconstructions. Our
findings reveal that despite dropping to near zero in the early 20th
century, the area burned in recent decades is within historical levels at
GILA and trends toward historical levels at SAGU. These results highlight
the magnitude of the post-1900 fire deficit and demonstrate that fire
management can restore the historically prevalent, ecologically important
process of widespread, frequent, low- to moderate-severity fire in dry
conifer forests.