Forest management not so hot at fighting warming

Environmentalists hoping that micromanaging Europe’s forests will help curb climate change may be barking up the wrong tree.

Retracing changes in forestry since 1750, researchers report in the Feb. 5 Science that forest management in Europe has made climate change worse, not better. Despite an overall uptick in tree populations, European forests stockpile less carbon than they did around 250 years ago. Furthermore, favoritism among foresters for certain tree species has resulted in forests that absorb more warming sunlight and undergo less air-cooling evaporation, the researchers found.

The net result is that forest management practices have slightly worsened warming, says study coauthor Kim Naudts, a forest ecologist at the Max Planck Institute for Meteorology in Hamburg. “We should not put our hopes in forest management to solve climate warming,” she says. “For Europe, it might be best to manage our forests for functions other than climate mitigation.”

Chopping down forests for fuel and farmland accounted for most of Europe’s impact on climate before the Industrial Revolution. Then, along with the fossil fuel boom, the continent began importing more of its food from other regions. These changes relieved some of the strain on Europe’s forests. After losing 190,000 square kilometers of forest between 1750 and 1850, Europe regained 386,000 square kilometers of forestland between 1850 and 2010 — an area roughly the size of Montana.

That bounce back, however, was closely controlled. In 2010, foresters managed more than 85 percent of European forests. Foresters plant and nurture tree species that provide ecological and societal benefits. This practice caused a sharp spike in the population of fast-growing, commercially valuable conifer trees such as Scots pine and Norway spruce at the expense of broad-leaved trees. Between 1750 and 2010, conifer coverage grew by 633,000 square kilometers while broad-leaved forest shrank by 436,000 square kilometers.

Naudts and colleagues reconstructed the climate impacts of the species changeover and other forest management practices. Conifer trees are darker and reflect less sunlight than their broad-leaved cousins. Conifers also lose less water to evaporation, a process which cools the surrounding air. Overall, forest management practices warmed local summertime air temperatures by about 0.1 degrees Celsius, the researchers estimate.

Conifers can hold more carbon than broad-leaved trees, but the harvesting of wood from managed forests overshadows that increase, the team found. Wood harvesting decreases the amount of carbon locked away in trees and strewn across the forest floor. That decrease is larger than the buildup of carbon in wood-based products, the team found.

The researchers now plan to investigate whether forest management has similar effects elsewhere. Climate impacts in North America will probably be different, says William Stewart, a forest economist at the University of California, Berkeley. That’s because “the species you find in managed forests are the same as you’d find [growing naturally] in the national parks,” he says.

Just because European forests aren’t combating climate change doesn’t mean that forest management practices need to be changed, says Benjamin Poulter, a forest ecologist at Montana State University in Bozeman. The effect of forest management on the climate is puny compared with that of fossil fuel burning, he says, and managed forests provide other, arguably more important benefits to the economy and local ecosystems.