Sub-Alpine Forests Absorb Less Carbon As Warming Occurs, Study Says

Contradicting the belief that trees will absorb more carbon dioxide as the world warms, a new study says that sub-Alpine forests in the western United States are likely to soak up less CO2 as temperatures rise and snowpack declines. Researchers at the University of Colorado found that while reduced snowpack generally advanced the onset of spring and extended the growing season, the decline in snow slashed the amount of water available to trees in summer and fall, causing them to less efficiently convert carbon dioxide into biomass. The researchers said that snow was much more effective at delivering moisture to trees than rain, and that as late as October, 60 percent of the water in the stems and needles of sub-Alpine trees can be traced back to snowmelt. That means that even if rainfall increases, the ability of sub-Alpine trees to absorb CO2 will decline if snowpack in the Rocky Mountains declines. “As snowmelt in these high-elevation forests is predicted to decline, the rate of carbon uptake will likely follow suit,” said researcher Jia Hu, whose study will be published next month in the journal Global Change Biology. Sub-Alpine forests account for roughly 70 percent of carbon storage in the western United States.