alaskan forests come back stronger!

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WAY WAY BACK IN 2004, when wild­fires in Alaska burned an area the size of Mass­a­chu­setts, Michelle Mack won­dered just how much carbon had per­ma­nently moved from the land­scape into the at­mos­phere. Mack, an ecol­o­gist at Northern Ari­zona Uni­ver­sity, knew that the carbon dioxide re­leased by these burning trees could fur­ther ac­cel­erate global warming.

But her study of re­growth in Alaska’s burned areas, pub­lished in the journal Sci­ence, turned out to be un­ex­pect­edly hopeful. The scorched bo­real forests are rapidly re­gen­er­ating. In fact, they are on track to hold a lot more carbon than they did be­fore the fires.

How is that pos­sible? Be­fore the fires, slow-growing black spruce trees had dom­i­nated the bo­real forest. In the se­verely burned areas, how­ever, faster-growing aspen and birch trees have largely re­placed them. These de­cid­uous trees suck carbon out of the air and trans­form it into wood much more quickly than the pre­vious ever­green forest.

“For me, it was sur­prising,” Mack said. “I didn’t think all that carbon could be offset. We keep talking about this run­away train of pos­i­tive feed­backs ac­cel­er­ating cli­mate change, but this looks like a brake.”

Mas­sive fires in the northern bo­real forests are be­coming more common: In 2019, fires raged for months in Al­berta, and mil­lions of acres rou­tinely burn in Russia. Bo­real forests tend to burn every 100 years or so, re­leasing carbon dioxide in the flames, then gath­ering it back in new growth. 

It’s a little like respiration—one breath per cen­tury. To figure out how this slow cycle is changing, the sci­en­tists working with Mack sur­veyed forest areas at var­ious stages of growth, map­ping out how carbon ac­cu­mu­lates. They also took mea­sure­ments over thir­teen years of soil carbon and tree growth at 75 sites that burned in 2004.

The above was lifted from “Rising from the ashes, Alaska’s forests come back stronger.”





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