You might not think of trees as being a fire hazard, but new research from a peatland in Alberta, Canada shows otherwise – at least for peat bogs. The research, published in Environmental Research Letters, compared sections of a peat bog near Highway 63 in northern Alberta. This Fort McMurray region was hit by a destructive wildfire in 2016 and scientists from McMaster University were interested in figuring out just why the fire was so bad.
The researchers specifically looked into the growth of black spruce, a tree species which grows well on dry peat. As you would expect, the older and taller a black spruce grows, the more shade it creates, thus blocking out the surface layer of moist sphagnum moss below it and essentially eradicating the damp “fire blanket” the moss usually provides. In addition, larger trees pull more moisture out of the ground, also making the peat beneath drier. These are the phenomena that the scientists think could have created the perfect wildfire conditions in 2016.
"There's a strong correlation between the size of the trees in the areas that were burned and how severe the burn was," says Sophie Wilkinson, the lead author of the study. "Where there's an area of known peat land and it has these big trees, that should act as a red flag for more awareness of greater fire risk."
It turns out that the trees don’t even have to be that much taller to make this difference for wildfire risk. Trees that measure only 5 meters tall, in comparison to their 2-meter-tall peers, can mean a larger risk for the peatland. In these areas, "It was very difficult to put out a section of the fire where the smoldering was very intense," says James Michael Waddington, a co-author of the paper. Firefighters who worked to put out the fire reported that the areas that had the largest trees were burned down to the mineral soil.
Peatlands are carbon sinks that store huge amounts of carbon dioxide in their midst and warming temperatures and subsequent drying from climate change already put them at risk of releasing huge amounts of CO2 into the atmosphere were a fire to occur. This new research determines that large trees may enhance also that risk. Because the stakes are so high, the authors recommend a short-term solution of removing large spruce trees in order to encourage the regrowth of sphagnum moss. As a longer-term solution, Wilkinson says we will need to find ways to moisten peat bogs in order to prevent smoldering wildfires.