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© Lora Denis
Boreal forest sunrise, northern Ontario © Rajinstan Kamalraj
Lurking underground in Canada’s boreal forests, zombie fires are the latest concern in an ever-growing list of issues arising from a changing climate.
Ever wondered how wildfires start so early in the spring, shortly after all the snow melts? Zombie fires – commonly known as holdover fires or overwintering fires – are often to blame. These are fires from the previous season that burned throughout the entire winter season by smoldering underground.
While zombie fires have only accounted for a very small percentage of total forest fires, there has been a dramatic increase in cases over recent years and the threat to Ontario forests may be increasing. British Columbia and Alberta have experienced approximately 10 times more zombie fires still burning as of early February 2024 compared to British Columbia’s 10-year and Alberta’s 5-year average.
You might wonder how a fire could survive underground for months at a time, under layers of both dirt and snow. The answer is peat, which is a layer of soil containing plant material that has been decomposing over tens to thousands of years. Peatland ecosystems are characteristic of many boreal forests in North America. With enough oxygen, fires could smolder and spread underground using peat as a source of fuel without a single flame in sight above ground. Then, as spring arrives and the snow melts, the fire could resurface if enough fuel is available and conditions are sufficiently warm, dry and windy.
Zombie fires are a sign of climate change and could contribute to increasing carbon emissions if left unchecked. Boreal forests and peatlands hold a great amount of carbon. Ontario’s peatlands alone hold more than all the province’s other ecosystems combined. When burned, the carbon contained in the trees and peat is released into the atmosphere, unable to return to the soil for hundreds of years while further contributing to climate change. This leads to a feedback loop as climate change results in drier and warmer conditions, which cause more severe fire seasons and zombie fires. Ultimately, those changes release more harmful emissions into the atmosphere.
Northern Canada is warming quicker than the global average. Last year’s record fire season is just one example of how the country continues to face warmer and drier seasons.
Although the idea of fires burning beneath the ground can be scary, it should not be a cause for panic. Zombie fires are rare in Ontario, and have mainly been an issue for British Columbia, Alberta and the Northwest Territories. However, they do act as an important sign for the severity of the upcoming fire season as well as an indicator for long-term climate trends. Therefore, it’s important to monitor them so that we can understand risk.
If you are curious on how to identify a zombie fire in the winter, the best sign to watch out for is a plume of smoke rising from the ground. Public reporting is an important tool that help local fire departments track and manage fires.
As a resident of Ontario, the most important thing you can do to manage fires locally is to follow your fire department’s guidelines. About half of all wildfires in Canada are started by humans. You can help mitigate the risks of starting a wildfire by following fire bans, discarding cigarettes responsibly, putting out firepits properly and never leaving fires unattended.
It is also important to note that not all fires are bad. Many forest ecosystems are adapted to fires, and the fires are a healthy natural cycle. However, the scale and severity of fires occurring due to climate change, and the effects that zombie fires have on forest regeneration after a fire demonstrate that there is a limit to what nature can withstand.
Northern leopard frog © Jozsef Szasz-Fabian