Strong Gradients in Forest Sensitivity to Climate Change Revealed by Dynamics of Forest Fire Cycles in the Post Little Ice Age Era

Abstract

The length of the fire cycle is a critical factor affecting the vegetation cover in boreal and temperate regions. However, its responses to climate change remain poorly understood. We reanalyzed data from earlier studies of forest age structures at the landscape level, in order to map the evolution of regional fire cycles across Eastern North American boreal and temperate forests, following the termination of the Little Ice Age (LIA). We demonstrated a well‐defined spatial pattern of post‐LIA changes in the length of fire cycles toward lower fire activity during the 1800s and 1900s. The western section of Eastern North America (west of 77°W) experienced a decline in fire activity as early as the first half of the 1800s. By contrast, the eastern section showed these declines as late as the early 1900s. During a regionally fire‐prone period of the 1910s–1920s, forests in the western section of Eastern boreal North America burned more than forests in the eastern section. The climate appeared to dominate over vegetation composition and human impacts in shaping the geographical pattern of the post‐LIA change in fire activity. Changes in the atmospheric circulation patterns following the termination of the LIA, specifically changes in Arctic Oscillation and the strengthening of the Continental Polar Trough, were likely drivers of the regional fire dynamics.

Recent fire activity in the boreal eastern interior of North America is below that of the past 2000 yr

“…Following the 1890 0 s fires, HBC archival records revealed that fire activity declined into the 1900s (Fritz et al 1993), which is consistent with information from the multi-proxy fire history. The advent of the 20th century marks a sharp transition toward a reduction of widespread synchronous fire years among large regions, likely brought by increases in the amount of precipitation associated with a strengthening of the Continental Polar Trough and jet stream displacement (St. George 2007, Drobyshev et al 2017). The 1988 fire, man-made, was the last large fire having hit the study area.…”

“…, Drobyshev et al. ). Albeit climate is likely to be a primary driver of this decreasing fire activity during recent decades, other confounding effects from European settlement and passive and active fire suppression may also have played a key role in driving these trends (Lefort et al.…”

“…The boreal forest is a dynamic system in which fire has always been a primary natural process, driving physical and biological attributes of the landscapes (Bowman et al 2013). For instance, in Canada fire has been an important disturbance shaping the boreal forest since the end of the last glaciation about 11,700 yr ago, and much of the current forest is the legacy of these past disturbances (Larsen 1980, Engelmark et al 1993, Stocks et al 2003, Boulanger et al 2017, Drobyshev et al 2017.…”

“…In contrast, areas of declining fire activity are reported in many southern boreal areas of eastern and western Canada, particularly in managed forests (Girardin et al 2013). These regions have experienced significant increases in summer precipitation since~1850 AD, likely brought by a strengthening of the Continental Polar Trough and jet stream displacement, which have contributed to increasing moisture content in deep-organic layers (St. George 2007, Meyn et al 2010, Girardin et al 2013, Drobyshev et al 2017. Albeit climate is likely to be a primary driver of this decreasing fire activity during recent decades, other confounding effects from European settlement and passive and active fire suppression may also have played a key role in driving these trends (Lefort et al 2003, Tardif 2004, Tardif et al 2016.…”

Hemiboreālo mežu degšanas vēsture un kokaudžu atjaunošanās degumos = Forest fire history and post-fire regeneration patterns in hemiboreal forests

“…Indeed, a vast majority of the studies looking at climate-fire interactions in the boreal zone has been done in Fennoscandia ( Aakala et al 2018) and references inside), a region experiencing a much stronger influence of North Atlantic climate as compared to more easterly located sections of EBZ. The increase in climate continentality towards easterly section of EBZ is be of particular interest in understanding the response of forest fire regimes to climate variability as previous studies have pointed to higher sensitivity of more continental boreal forests to historic climate changes Drobyshev et al 2017).…”