Six independent tree-ring reconstructions of summer drought were calibrated against instrumental fire data to develop a 229-year dendroclimatic-inferred record of fire activity (annual area burned and fire occurrence) on the Boreal Shield, Canada. As a means of validating the statistical reconstructions of the fire activity, a comparison was made with a stand age distribution derived from a regional time-since-last-fire map for an area located at the transition between the mixedwood and coniferous boreal forests of south-western Quebec. Calibration statistics indicated that 31% of the area burned variance and 45% of the fire occurrence variance could be accounted for by the six drought reconstructions. The verification statistics indicated a tendency for the statistical reconstructions of the fire activity to reproduce with confidence both high and relatively low frequency variations in fire. Episodes of succeeding years with important fire activity were estimated for 1789–1796, 1820–1823, 1837–1841, 1862–1866, 1906–1912, 1919–1922, 1933–1938, and 1974–1977. Also estimated were periods of reduced forest fire activity, particularly in the occurrence rate of extreme fire years, from c. 1850 to 1900 and again during the second half of the 20th century. Correlation analysis between the statistical reconstruction of the area burned and the stand age distribution suggested that both proxies shared similar information on the fire activity. Correlation maps, however, indicated that variability in the statistical reconstructions was not necessarily representative of fire activity in all regions of the Boreal Shield.
Human-caused climate change is now a key driver of forest fire activity in the western United States
