Black Spruce: The Fire King

Typical high-intensity crown fire in Canada. Photo courtesy of Brian Stocks.

Typical high-intensity crown fire in Canada. Photo courtesy of Brian Stocks.

Typical low-intensity surface fire in a Scots pine forest of central Siberia. Photo courtesy of Douglas McRae.

Typical low-intensity surface fire in a Scots pine forest of central Siberia. Photo courtesy of Douglas McRae.

Landscape after a severe black spruce crown fire in interior Alaska. Photo courtesy of Scott Rupp.

Landscape after a severe black spruce crown fire in interior Alaska. Photo courtesy of Scott Rupp.

Falmouth, Mass. – Boreal forests represent one third of global forest capital and because warming is occurring at least two times faster in the high northern latitudes, these forests could play a leading role in the global climate system. A new paper published in Nature Geoscience led by Woods Hole Research Center scientist Brendan Rogers finds that fires in Eurasian forests impact the climate system quite differently than those in North America, and that individual tree species are to blame. The paper concludes that these differences must be taken into account for accurate climate modeling in the future.

Wildfires are a part of the natural processes occurring within most boreal forests, but the fires burn differently by continent. High-intensity crown fires are more common in North America whereas low intensity surface fires are frequent in Eurasia. This study combined remote sensing and climate reanalysis data with forest inventories to compare boreal fire dynamics between the two continents. Dr. Rogers and colleagues found that Eurasian fires were less intense and less destructive, resulting in different climate feedbacks. In particular, the loss of leaves and branches from North American fires expose underlying snow and allow more sunlight to be reflected in spring. This has a cooling effect on the climate. In Eurasian forests where tree cover remains relatively intact, this effect is much smaller. Added to the warming from emitted CO2, the overall impact is thought to be neutral or warming.

The researchers identified species-specific fire traits in each of the two systems that strongly influence the different fire regimes. In North America, for example, tree species known as “fire embracers” have evolved to spread and be destroyed by fire. Mature stands of black spruce, which are ubiquitous in Canada and Alaska, burn like a torch and cause intense crown fires that kill the canopy. In Eurasia, on the other hand, the thick bark and sparse lower branches of “fire resisters” allow them to largely survive flames, which creep along the forest floor consuming underbrush. According to the study, because the fires in Alaska and Canada are dominated by black spruce, this phenomenon may represent the single largest influence of individual species on continental-scale patterns of carbon and energy flow, except for humans.

This is important for creating accurate Earth system models. According to Dr. Rogers, “Current global fire models neglect the influence of these species-level traits and misrepresent boreal fire feedbacks to climate warming. We need to move beyond generic representations of trees, and use this information to make informed decisions on how to manage forest fires for climate mitigation.”

This work was financially supported by the US National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA).

Link to abstract »


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