We've been taught all our lives that one of the best ways to mitigate the effects of climate change is by planting more trees that could absorb and reduce levels of carbon dioxide in the atmosphere.
Turns out, this doesn't always lead to the desired effect, a new study revealed.
Some Trees Worsen Warming
Switching to dark conifer trees from broad-leafed ones may have contributed to the rise of average temperatures in Europe.
Researchers from France noted that changes in forest management have pushed summer temperatures in the continent to increase by 0.12 degree Celsius (0.2 degree Fahrenheit) since 1750.
Many European nations had decided to plant conifer trees such as spruce and pines. These trees' dark colors trap the sun's heat and allow more sunlight to be absorbed, scientists said.
Aside from that, conifers are more conservative with water. Kim Naudts, lead author of the study, said this leads to less evapotranspiration - the process in which water is transferred from land to the atmosphere by evaporation from the soil and transpiration by plants - and drier air, which had also contributed to warming.
On the other hand, broad-leafed trees with light colors and flat leaves -- including birch and oak trees -- reflect more sunlight back into space. As Europe expanded its forests to conifers, however, it had to give up its broad-leafed trees.
Fast-growing conifers dominated forests and everything else since then. Conifers stretched to additional 633,000 square kilometers (244,000 miles) of land, while broad-leafed cover was reduced by 436,000 square kilometers (168,000 miles). Thus, the effect took place.
While increasing conifer cover should have had a positive effect on the climate, researchers found that forests in Europe accumulated a "carbon debt." This meant that European forests have released 3.1 billion metric tons of carbon into the planet's atmosphere since the switch to conifers occurred.
How so? Naudts said humans had extracted wood from unmanaged forests, removing their capacity to store carbon.
"Even a well-managed forest today stores less carbon than its natural counterparts in 1750," said Naudts.
"If the point is to store carbon, then afforestation is presumably good, but losing carbon to wood extraction is bad," added Richard Houghton, an ecologist from the Woods Hole Research Center.
But it's not all about carbon. Naudts said government policies regarding forest management should be re-considered to take into account other factors such as the color of trees and their changes to moistures and soils.
Researchers concluded that European forests have not resulted to the climate benefit that some might have hoped for.
"Two and a half centuries of forest management in Europe have not cooled the climate," the authors of the study wrote.
It may not even be an isolated case, although the study is restricted to Europe. Experts say similar effects are likely to be occurring in other parts of the world with big forest planting programs, including the United States, Russia and China.
Another study conducted by the European Commission provides evidence that could support Naudts' and her team's findings. The report, which is featured in the journal Science, found that the loss of forests all over the world has led to an increase in maximum and average global temperatures, particularly in tropical and arid regions.
Photo: Kathrin Rieger | Flickr