As the climate warms and the growing seasons lengthen, subalpine forests are likely to soak up less carbon, according to a new University of Colorado study.

“Our findings contradict studies of other ecosystems that conclude longer growing seasons actually increase plant carbon uptake,” said Jia Hu, who conducted the research as a CU graduate student in evolutionary biology.

Hu worked with Russel Monson, a senior fellow at CU’s Cooperative Institute for Research and Environmental Sciences, on the study, which was published today in the journal Global Change Biology.

The researchers found that while smaller spring snowpack tended to advance the onset of spring and extend the growing season, it also reduced the amount of water available to forests later in the summer and fall.

The water-stressed trees were then less efficient at converting the carbon dioxide into biomass. The summer rains were not enough to quench the trees’ thirst.

“Snow is much more effective than rain in delivering water to these forests,” Monson said. “If a warmer climate brings more rain, this won’t offset the carbon uptake potential being lost to declining snowpacks.”