Forests’ vanishing snow is also bad news for carbon storage

Many forests lose their winter snowpack as global temperatures increase, which could slow their growth considerably – and reduce the amount of carbon that they remove from the atmosphere.

The current projections “do not incorporate this complexity of winter climate change, so they probably overestimate what the future carbon storage will be”, explains Emerson Conrad-Rooney at the University of Boston in Massachusetts.

Warming temperatures should generally increase the growth of temperate forests, mainly by stimulating decomposition and by making more nutrients available during the hot growth season. However, the models do not take into account changes during the winter – especially the loss of snow.

“The loss of deep and insulating snowy mantle cannot be underestimated,” explains Elizabeth Burakowsi at the University of New Hampshire. His research has shown that deep snow days will disappear in most of the United States by the end of the century, with consequences for the storage of water and the health of the ecosystem.

To better understand these changes in cold weather, Conrad-Rooney and their colleagues simulated how a global temperature increase of 5 ° C would affect the growth of red maples (Acer Rubrum) In an experimental forest in New Hampshire. In some plots, they used buried cables to warm the ground during the growth season. In others, they also removed snow during the winter and warmed the ground to induce cycles of frost and thaw.

Measured over 10 years, the trees of the two plots have increased more than the trees that have been left alone. However, the plots where snow has been removed has increased much more slowly, adding about half of the growth. The researchers attribute this difference to the damage of the roots caused by the soil without snow exposed to the evolution of the temperatures.

“Snow generally acts as an insulating blanket to prevent the floors from freeze,” says Conrad-Rooney. “With less snow, there are more freezing cycles.”

The extrapolation of similar forests across the northeast of the United States, the researchers believe that the loss of snowpack expected by the end of the century would reduce carbon storage by just over a million tonnes per year, compared to models that do not take into account the disappearance of snow.

“The snowy coats that come and go throughout the winter decrease the stable soil conditions that our northeast ecosystems need for long-term carbon storage,” says Burakowski.

However, not all the snow-capped forests respond to the loss of snow-handled in the same way as northeast leaf forests, explains David Bowling at the University of Utah. He emphasizes that the precise modeling of various ecological responses remains a great challenge. “There are so many things that change,” he says.