As boreal forests recover from severe wildfire events, which release long-stored carbon, shifts in their tree species makeup can offset this carbon loss, a new study finds. Some forests, as they grow back, can store nearly five times more soil carbon than others, the results show. Wildfires can affect climate warming by altering the balance between the amount of carbon sequestered by growing forests and that released into the atmosphere over time. Severe wildfires, like those more often seen in the boreal forests of North America, burn hot and over large areas and can combust organic soils below the ground's surface, releasing long-stored carbon. If wildfires are causing more carbon to be released than can potentially be reaccumulated through forest regrowth, they could accelerate climate warming. Understanding whether carbon storage during forest recovery after intense fires compensates for that released during burning is crucial for determining wildfire's overall impact on future climate warming. Michelle Mack and colleagues report on a 15-year-long study of wildfire impacts on forest regeneration and the carbon balance of Alaskan boreal forests. Mack et al. found that following wildfires, the species composition in a majority of their study sites changed, shifting from slow-growing black spruce to a mix of conifers and fast-growing deciduous tree species, like aspen and birch. According to the study's results, forests that shift to deciduous dominance after severe burning can store nearly five times more soil carbon than the stands that return to black spruce. The findings suggest that carbon loss through fire is temporary and more than compensated for by subsequent deciduous forest succession. And, once established, these forests could maintain carbon storage longer, providing a negative or stabilizing feedback to climate warming.
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Journal
Science