Seeing the forest for the trees: Why latest tree census matters

Earth’s forests hold over 3 trillion trees, over seven times the number estimated previously, according to a new study. This is good news for tree huggers.

But environmentalist cheers might fade at the other revelation of the study: The Earth’s trees have been nearly chopped in half since human civilization began.

Researchers estimated that there were 5.6 trillion trees when agriculture began. 

Study author and Yale forestry researcher Thomas Crowther, doesn’t think it’s a coincidence that forests have shrunk as human civilization has grown.

"Humans are diminishing that huge population on such a global scale," Dr. Crowther told the Associated Press.

Crowther found that about 15 billion trees are chopped down for human use annually. Although 5 billion trees are replanted each year, losing a net about of 10 billion trees each year is significant.

The study, published in the journal Nature on Wednesday, was launched in part by Plant for the Planet, a group looking to plant new trees to combat the human impact on the Earth.

The researchers used a combination of data from surveys on the ground and satellite image to tally the Earth’s trees.

Environmentalists may be pleased that the count of 3.04 trillion trees is significantly higher than the previous estimate of 400 billion. But, Crowther said in a news release, “We’re not saying, ‘Oh, everything’s fine.’ ”

Not all trees, or forests, are the same.

“The number of trees is just one piece of the puzzle,” said biogeochemist Susan Trumbore of the Max Planck Institute for Biogeochemistry in Jena, Germany, in the release. “A tree in the tundra is not the same as a tree in the rainforest.”

Dense forests hold a significant amount of carbon dioxide. Climate scientists attribute about 10 percent of annual global carbon increase to the effects of deforestation.

Trees are like sponges for carbon dioxide, feeding off the compound as they grow. Throughout its lifetime, a tree traps carbon dioxide into its roots, trunk, branches, and leaves. In the process, the tree emits fresh oxygen. 

Crowther’s team calculated that tropical moist forests hold the most trees of any biome, but are quickly losing ground. More than half of deforestation is occurring in tropical forests, according to a recent study by the World Resources Institute.

Boreal forests, containing coniferous trees and patches of permafrost, are also shrinking. These forests stretch across areas formerly covered by glaciers in North America and Eurasia. 

Many forests have become fragmented by deforestation. Today, just the Amazon and the Congo remain as large swatches of continuous forest. 

But there are some victories for climate scientists and environmentalists to celebrate. Tropical deforestation is slowing, a report revealed in 2014. In the 1990s, about 40 million acres of tropical forests were claimed by deforestation each year. Now, about 32 million acres are lost annually.

“These forests are the lungs of the earth,” Glenn Hurowitz, managing director at Climate Advisers, a carbon policy advocacy organization, told The Christian Science Monitor in 2014.

This report includes material from the Associated Press.