Wildfires- The Old World and the New

A canopy forest-fire burns through black spruce forest on a hillside near Fairbanks, Alaska.

A canopy forest-fire burns through black spruce forest on a hillside near Fairbanks, Alaska.

As of this morning, 4,698,861.3 acres have burned in the State of Alaska this summer. If season-ending rains don’t arrive soon, we are on track to best the 2004 total of over 6 million acres. To put these huge numbers in perspective, the entire state of Massachusetts is around 5 million acres.

That’s a lot of forest going up in towering plumes of smoke. And that’s a bad thing, right? Well, if you live, as I do, in the boreal forest, and spend too many summer days choking on forest fire smoke, and worrying about the risk to my little cabin in the woods, then a big fire year is hardly welcome. From an environmental perspective however, it’s a more complicated story.

Forest fires warrant a whole series of posts, (which I may get to at some point), but for now, I want to share something about fire that I just learned, and found utterly fascinating.

The boreal forest is one of the largest ecosystems on the planet. It’s circumpolar, wrapping around the subarctic areas of North America, Asia, and Europe. The structure and biodiversity of the boreal forest are largely dictated by fire. This is true across the planet, but fires in the old world and the new are not, by any means, the same.

Forest fire smoke blows over the boreal forest of interior Alaska.

Forest fire smoke blows over the boreal forest of interior Alaska.

A couple of weeks ago I was driving north out of Fairbanks along the Elliott Highway. The Aggie Creek Fire is burning about 30 miles north of town and across the highway. The day I passed, it wasn’t particularly active, with just a few hot spots throwing up plumes of white smoke into the otherwise blue sky. The crews of fire-fighters were hard at work, and their vehicles crowded the shoulders of the road. I paused to watch one particular hotspot where I could see flames charring the trees. The fire was winding up a slope, following a stand of black spruce like a road. The neighboring patches of birches remained green. The fire loved that black spruce.

Large portions of the boreal forest of Alaska and Canada is made up of black spruce. These scruffy-looking little trees are extremely fire-prone and stands of this species burn, on average, about once every 100 years. In fact, the species has evolved in concert with fire, and their reproductive strategy, involving cones that pop open in extreme heat, is closely tied to wildfire.

Black spruce forests go up like matchsticks. The fire climbs the low branches, rises into the canopy, and torches the entire tree leaving little but a vertical stick behind.

Black spruce forests go up like matchsticks. The fire climbs the low branches, rises into the canopy, and torches the entire tree leaving little but a vertical stick behind.

Old-world boreal forests however don’t have black spruces and fires there, while just as frequent, tend to remain in the understory. The forests of the old world are dominated by deciduous larches which are fire-resistant, and usually survive the burns that pass through the understory beneath their branches.

An interesting factoid no doubt, but this post-burn difference, (the completely fried black spruce forests of North America, vs. the still intact canopy of the old-world boreal forest) has a surprising side effect.

For more than half of each year, the world’s boreal forests are draped in snow. Take a moment to picture the two types of burned forest from above. The Eurasian forests will look more or less the same whether recently burned or not. The intact trees will look like a series of dark circles against the snow, with tree density dictating how much snow is visible. In North America however, a burned forest will look like a scattering of pin pricks on a sheet of printer paper. From above, it’s almost all snow.

A burned black spruce forest in winter.

A burned black spruce forest in winter.

In North America, on the other hand, burns result in millions of acres of unbroken winter snow. Snow that neatly reflects solar radiation right back into space.

Why does this matter? Well it may matter a whole lot when it comes to the global climate. Eurasian forest fires kick tons of carbon dioxide into the atmosphere while retaining an intact, dark, heat-absorbing canopy. In North America, on the other hand, burns result in millions of acres of unbroken winter snow. Snow that neatly reflects solar radiation right back into space. This is such a profound effect, that according to a recent paper in the journal Nature Geoscience, fires in North America, despite the carbon release, may actually have a net cooling effect on the planet. So strong is this effect that the authors of the paper theorize the cooling may be twice as strong as the warming impact of the carbon and aerosols emitted by the fire.

My mind is still spinning over this one, and I’m genuinely curious to see if followup studies yield similar findings. Whether the results hold up or not, this is a fascinating example of how different habitats within the same global biome can react in varying ways to landscape impacts like fire. Pretty cool, or hot, depending on how you look at it.

Information for this post came from the following article:
Rogers et al. 2015. Influence of tree species on continental differences in boreal fires and climate feedbacks. Nature Geoscience 8: 228-234.

1 comment for “Wildfires- The Old World and the New

  1. Kurt
    July 19, 2015 at 4:43 am

    I’m curious of the shading effect of that much smoke in the air might also play a role.

Comments are closed.