Data From: Spatiotemporal synchrony of climate and fire across North America (1750-1880)

After a policy of aggressive fire suppression in most of North America
during the 20th century, increasing aridity has driven widespread,
synchronous fire occurrence in recent decades. A lack of historical
(pre-1880) fire records limits our ability to understand long-term
continental fire-climate dynamics. The goal of this study is to use
tree-ring reconstructions to determine the relationships between
spatio-temporal patterns in historical climate and widespread fire
occurrence in North America, and whether they are stable through
time.  We applied regionalization methods to tree-ring
reconstructions of historical summer soil moisture and annual fire
occurrence to independently identify broad- and fine-scale climate and
fire regions based on common inter-annual variability. We then tested
whether the regions were stable through time and for spatial
correspondence between the climate and fire regions. Last, we used
correlation analysis to quantify the strength of the fire-climate
associations through time. We found that broad-scale historical patterns
in climate and fire have strong spatial coherence. Although climate and
fire regions vary over time, large core areas of the regions were stable.
The association between climate and fire varied through time and was
strongest in western North America, likely due to a combination of
factors, such as the magnitude of drought frequency and severity, as well
as varying use of fire by human communities. The historical perspective
gained through tree-ring reconstructions of climate and fire patterns and
their association suggests that the recent climate-driven synchrony of
fire across large areas in recent decades is not unprecedented, will
likely continue into the future, and may exhibit similar spatial patterns.