Climate and wildfires in the North American boreal forest

Abstract

The area burned in the North American boreal forest is controlled by the frequency of midtropospheric blocking highs that cause rapid fuel drying. Climate controls the area burned through changing the dynamics of large-scale teleconnection patterns (Pacific Decadal Oscillation/El Niñ o Southern Oscillation and Arctic Oscillation, PDO/ENSO and AO) that control the frequency of blocking highs over the continent at different time scales. Changes in these teleconnections may be caused by the current global warming. Thus, an increase in temperature alone need not be associated with an increase in area burned in the North American boreal forest. Since the end of the Little Ice Age, the climate has been unusually moist and variable: large fire years have occurred in unusual years, fire frequency has decreased and fire-climate relationships have occurred at interannual to decadal time scales. Prolonged and severe droughts were common in the past and were partly associated with changes in the PDO/ENSO system. Under these conditions, large fire years become common, fire frequency increases and fire-climate relationships occur at decadal to centennial time scales. A suggested return to the drier climate regimes of the past would imply major changes in the temporal dynamics of fire-climate relationships and in area burned, a reduction in the mean age of the forest, and changes in species composition of the North American boreal forest.

The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model

“…However, this variation is still constrained by the short temporal depth of the years of record in the CLDN lightning strike data set (Orville et al, 2002;Kochtubajda and Burrows, 2010). Synchronicity in major fire activity years across provinces (e.g., 1961, 2005, 2007) was consistent with several studies on fire history, suggesting that changes in forest fire activity have been observed jointly over vast areas since the 1900s (e.g., Bergeron et al, 2004b;Macias Fauria and Johnson, 2008).…”

“…Multidecadal temporal changes in annual burn rates reflect the underlying influence of climate variability and extreme fire weather (Macias Fauria and Johnson, 2008;Girardin et al, 2009); these multidecadal temporal changes were well represented in the input climate data sets. An increase in temperatures and stability in precipitation between 1916 and 1924 ( Fig.…”

“…S9) could be at the origin of a high frequency of fire occurrence during those years, marking a pause in the decline of fire activity that had been observed since the 1850s (Bergeron et al, 2004a). Advection of humid air masses over eastern Canada between 1940 and 1970 contributed to the creation of moister conditions, which can lessen the capacity of a fire to spread after a lightning-induced fire ignition (Macias Fauria and Johnson, 2008). Both interannual variation and unsynchronized trends in climatic variables may have brought about changes in fire activity and could have affected the fire season, as it is proposed to have occurred over millennial timescales during the Holocene (Ali et al, 2012).…”

Landscape composition influences local pattern of fire size in the eastern Canadian boreal forest: role of weather and landscape mosaic on fire size distribution in mixedwood boreal forest using the Prescribed Fire Analysis System

“…This is mainly because the Canadian boreal forest is quite large and covers different forest types, but also because both factors may not act at the same spatial scales. Previous studies showed that climate may be the first-order driver for fire on continental and subcontinental scales (Johnson 1992;Girardin 2007;Macias Fauria and Johnson 2008), mainly owing to positive 500-hPa geopotential height anomalies persisting over a given region for days (Johnson and Wowchuk 1993) and lightning strikes providing the ignition source (Flannigan and Wotton 1991). The present study showed that when fires are analysed as spatial processes taking place at the landscape level, weather related to propagation is the most important factor influencing fire size, followed by the forest fuel composition and to a lesser extent by weather conditions directly related to fire ignition (DMC).…”

How important is biomass burning in Canada to mercury contamination?

“…De Simone et al (2017) investigated the effects of including PBM emitted from biomass burning, and found that this fraction is reduced to 62-71%, indicating that more mercury is deposited closer to the fires, on land, when PBM is emitted in the model. The frequency of large fires, and thus area burned, in Canada has increased in the last four decades of the 15 20 th century (Fauria and Johnson 2008). Changes in forest fires may be the greatest early impact of climate change on forests.…”