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Climate Change and Wildfires Could Reshape Boreal Forests and Offset Carbon Cycling
Climate Change and Wildfires Could Reshape Boreal Forests and Offset Carbon Cycling

Portland State University recently received a $1.4 million grant from the National Science Foundation (NSF) in support of a study led by PSU research assistant professor Melissa Lucash (Geography). The study will improve our understanding of how climate change and repeated exposure to wildfires could affect vegetation, permafrost, and the vast stores of carbon within the boreal forests of Alaska.

Dominated by spruce, the boreal forests of the Alaskan interior cover millions of acres and have remained relatively unchanged with regards to species composition and biogeochemical processes for roughly 6,000 years. While these frigid, northern forests comprise just 18% of the total land area of the US, they contain more than half of the country’s forest carbon, with much of that stored belowground. However, threatened by repeated wildfires burning the same tracts of land at intervals more frequent than the forests can cope with, the long-term stability of this resource is at risk. Add to that the effects of climate change, which could result in temperatures in the region rising anywhere between 2–8˚C by the end of the century, and there is the possibility that the landscape could experience dramatic changes and a disruption of the region’s ability to absorb and store carbon.

Historically, intervals between wildfires were often long enough (multiple decades or even centuries) for the spruce forests to regenerate, but that pattern changed in the late twentieth century with some areas experiencing burns every four to ten years. The increasing frequency of fires, according to Lucash, a forest ecologist, could result in shifts in species composition in those areas hardest hit. Depending on the outcomes, those changes in fire periodicity and species composition could impact carbon cycling to varying degrees. If spruce forests give way to hardwood forests, for example, there would likely be an increase in the forests’ ability to store carbon. But if repeated wildfires prevent hardwoods from repopulating and grasses become the dominant species in the region, that shift, then, could cause a profound weakening of carbon sink strength. Determining what factors lead to “tipping points” for one vegetation type or another and the effects of those shifts on carbon cycling aboveground and belowground in relation to a warming climate is at the core of Lucash’s NSF-funded study.

“The idea is that, with repeated wildfires, the conifers may be unable to repopulate the forest,” Lucash said, “and then there is a shift to hardwoods. Eventually, if the same areas continue to experience wildfires, there could be a shift from hardwood forests to a landscape dominated by grasses. The goal of this study is to gain a better understanding of what causes these tipping points and where they occur, and to quantify the potential changes to carbon sinks, stocks, and vegetation in boreal forests due to climate change and repeated wildfires.”

The study combines fieldwork in areas of the Alaskan interior that have experienced single and multiple burning events over the past several decades with spatial modeling that will allow the research team to simulate changes in the forest over time and under various climate change scenarios. Experts in landscape and disturbance ecology, permafrost, hydrology, and biogeochemistry from universities in Alaska, Florida, Idaho, and North Carolina have joined Lucash on the research team. The study also provides field research opportunities for Native American high school students from the Rural Alaska Honors Institute and supports a partnership with Your World Rocks, a nonprofit organization of scientists and engineers that does creative and interactive class presentations in Oregon elementary schools at no cost.

“Spruce has been the dominant species in these Alaskan Forests for thousands of years,” Lucash said, “but, in a matter of decades, under pressure from repeated wildfires, we’re starting to see that dominance waiver. We need a better understanding of when and where these forests will reach their tipping points and what species will move in. It’s likely we’ll see hardwoods or grasses replacing spruces, with hardwoods taking up more carbon and grasses taking up less. Regardless, these changes in species composition and warming temperatures will have implications for carbon cycling. The boreal forests are a huge storehouse of carbon, and even small changes in carbon stocks and rates of uptake can have a big impact on the global carbon cycle.”