Trees sequester carbon from the atmosphere and play a key role in mitigating the effects of climate change. But a study by researchers at Dartmouth College found that from a climate perspective, forestation isn’t necessarily a good thing in all cases. They concluded that deforestation may provide greater climate benefits in some areas than leaving trees standing. Their study, published in the journal Climatic Change, is the first to put a value on albedo, a measure of the snow’s ability to reflect the sun’s energy.
“In many areas where snow is frequent, the overall climatic influence of the high albedo from snow may counteract the cooling benefits of carbon storage,” said postdoctoral researcher David Lutz.
Lutz and colleague Richard Howarth agree that sustainable forestry practices provide important climate benefits in forests with high growth rates. But at high latitudes where snowfall is common and timber productivity is low, an open landscape with a large field of snow can have a cooling effect by reflecting incoming solar energy, outweighing the value of lost carbon storage. They suggest that snow-cover albedo be factored into existing and proposed carbon trading programs, like the California Greenhouse Gas Cap-and-Trade Program run by the California Air Resources Board, which they say is already generating forest carbon projects in New England.
In their study, the researchers created what they call an integrated assessment model that places an economic value on timber, as well as on albedo and carbon, and examined how these values would affect forest harvesting rotations in the White Mountain National Forest. Their results suggest that the value of albedo can shorten optimal forest rotation periods significantly compared to scenarios where only timber and carbon are considered. In high-elevation areas near tree-line that receive substantial snowfall, and where forests grow slowly, the optimal forest size from a climate-cooling perspective is near zero.
The researchers recognize that deforestation may have significant negative effects on biodiversity, wildlife habitat, and other ecosystem services, so they recommend that forest managers consider those factors when working to maximize timber production, carbon storage, and albedo at mid- and high-elevation forests. “My hunch is that the working forest concept with sustainable management practices is the best option for our region,” said Howarth, “taking into account the diverse values associated with forests and the links between communities and landscapes. But the science of how forests interact with climate is an important piece of the puzzle, and that’s more complicated than a simple focus on carbon.”
Lutz and Howarth are now expanding their model to evaluate more than 500 forest sites across New Hampshire to include many different tree species, varying elevations, and differing amounts of snow cover. They also plan to incorporate a wide range of other forest values into their model, from shelter and foraging habitat for wildlife to recreational, cultural, and aesthetic values. “We’re adding these aspects one at a time at the moment,” Lutz said. “From that standpoint, we are far from making any prescriptive statements about what forest owners should or should not do.”