An international team of more than 60 researchers spent eight years determining what kind of forest is best at removing carbon from the air. They planted more than 150,000 trees into plots with between one and 16 species.
By the end of the experiment, the most diverse plots had amassed over twice as much carbon as the plots with a single species — an average of 32 tons per hectare compared with 12 tons. And the effects might be even greater when applied at a bigger scale, the researchers wrote in the journal Science.
The results come at a bleak time for climate policy, as scientists put the finishing touches on a United Nations-backed report expected to warn that time is nearly out to hold warming below 1.5 degrees Celsius. Some experts say emissions reductions alone aren’t enough to meet that threshold; it will take unproven technology to suck carbon from the air, they argue.
There’s a contingent of researchers exasperated by that mindset. Instead of banking on some hypothetical breakthrough, they say the world should rely on the carbon-storing power of forests.
“While high-tech carbon dioxide removal solutions are under development, the ‘natural technology’ of forests is currently the only proven means of removing and storing atmospheric CO2 at a scale that can meaningfully contribute to achieving carbon balance,” said a statement from the Climate and Land Use Alliance and signed by 40 researchers.
Forests currently absorb about one-quarter of the carbon from human emissions, but wildfires and other events threaten to disrupt that. The United States is struggling to respond to those threats because of congressional inaction.
A recent lapse of the Land and Water Conservation Fund means funding has halted for conservation projects in existing forests, and the stalled farm bill means reforestation efforts aren’t getting any new money either, said Jad Daley, president of the nonprofit American Forests.
The LWCF could make a big difference in the Southeast, where fast-growing cities are spreading into wooded areas, and the farm bill could spur reforestation in the lower Mississippi River Valley, where lots of trees were cut for farmland, Daley said.
The picture is brighter in China, which planted 1.5 million hectares of trees each year between 2010 and 2015.
But many of those new tree stands were monocultures, the researchers wrote, adding that China could sequester much more carbon simply by adding more species to the mix.
The results supplement another finding from earlier this year: The amount of carbon stored in a tree stand depends almost as much on species variety as it does on age.
Each additional species brought more than 6 percent additional carbon storage in tree stands of up to 20 species. That study, based on natural observations in a southeast China forest and published in the Proceedings of the Royal Society B, was conducted by some of the same researchers as the Science study.
“Now we have reached the same conclusion with an experiment under controlled conditions: a forest with a large number of tree species is more productive than a monoculture,” the Chinese Academy of Sciences’ Keping Ma, co-manager of the project, said in a statement.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.