A study led by University of Michigan researchers and published recently in PNAS reports that cold-climate forests are not adapting to climate change as effectively as carbon sinks as we thought. While previous predictions have shown cold-climate forests at high latitudes becoming more productive with more availability of CO2 (and thus, more efficient carbon sinks for us), a team of international experts says that the narrative is more complicated than that.
We depend greatly on trees and vegetation for their ecosystem services of shelter, resources, and water purification, amongst others. But by far our largest dependency on trees comes from the role that they play as carbon sinks, sequestering carbon dioxide from the atmosphere where is acts as a greenhouse gas and worsens global warming, into their own nutrients for growth. In fact, trees absorb roughly 30% of the carbon we pump into the atmosphere by burning fossil fuels.
The study characterizes the seasonal flux of carbon in order to carry out its analysis. Carbon flux can be measured quite precisely by following the seasons – as plants absorb CO2 in the atmosphere in the spring and summer as they grow and release it in the fall and winter as they go dormant, die, and decompose.
The team shows that previous models categorized by latitude do not accurately explain what is happening. For instance, they exemplify how the amount of carbon Siberian forests contribute to the planet's seasonal carbon flux has increased much more than that of other forests at similar latitudes. According to Science Daily, the seasonal carbon uptake in Siberian forests has increased four times more than that of North American boreal forests since the 1980s.
"This research shows that we need to be thinking differently about how we understand the carbon cycle," said study co-author Gretchen Keppel-Aleks, U-M assistant professor of climate and space sciences and engineering. "We can't just lump ecosystems together by their latitude. We need to be thinking about individual species and specific seasonal cycles of temperature and precipitation."
The stratified carbon flux across different forests of similar latitudes suggests that we need to completely rework the structure in which we had been basing such models. While certain forests may indeed keep increasing their carbon uptake (ie. Siberia), others (ie. North American) may either flatline or potentially decrease carbon uptake.
"Going forward, we need to make sure our carbon budgets and models are fully incorporating what's happening in Alaska and Canada, as these patterns are largely not captured in models and the region may soon transition from a carbon sink to a source," says Brendan Rogers of Woodwell Climate Research Center (formerly Woods Hole Research Center).