Long-term fire regime variability in the eastern Canadian boreal forest: Climate versus local factors influences

Background/Question/Methods

Current global warming is expected to increase both the fire occurrence and area burned in a large part of the world’s boreal forests, which will have severe environmental and economical consequences. In Canada, an increase in extreme fire events during the last few decades largely supports this scenario. Few studies focus on the influence of local factors on fire regimes at the millennial time-scale. Local non-climatic drivers on fire regimes could influence vegetation patterns and result in high spatial variability at the landscape-scale. Current challenge is to differentiate the influences of climatic versus local factors on fire regimes variations. Thus, understanding the roles of climatic and non-climatic factors is essential to better-forecast how fire regimes will change in response to global warming. We use charred particles preserved in four lacustrine deposits in a restricted area to investigate the role of climatic and local non-climatic factors on the fire regime of the boreal forest in eastern Canada over the last 8000 years. Fire-free intervals distribution and synchrony in fire episodes amongst the sites, were used to estimate the importance of climate versus local-scale fire regime drivers. We

Results/Conclusions

Between 8000 and 5800 cal. BP climatic conditions were less conductive to fire events. After 5800 cal. BP, a progressive increase in fire frequency is recorded. High fire frequency characterizes the period extending between 4200 and 800 cal. BP. A decrease in fire frequency characterizes the last 800 years. Between 8000 and 4000 cal. BP the site display comparable fire-free interval and synchrony in fire episodes. During this period climate controlled predominantly the fire regime in the study area. By 4000 cal. BP two sites show independent fire history (different median and fire-free interval distributions and/or asynchronous in fire episodes), underlining the importance of local factors such as daily humidity of the combustible, the watershed and/or landscape connectivity in fire ignition. We assume that climatic changes during the last 4000 years, which induced variations in the water table and fire frequency, may be responsible to this high spatial heterogeneity in fire history. We conclude that current global climate changes could induce such high spatial variability in fire regime, but it is difficult to assess consequences in ecosystems dynamics.