The latest NASA research suggests that we may have been overestimating the amount of carbon stored by temperate US forests.
Current estimates are based on cutting down a sample of an average of 30 trees of each species across the country, and then using mathematical models to scale up the measurements, but that gives incomplete data.
“Estimates of the carbon content of living trees typically rely on a method that is based on cutting down trees,” said Laura Duncanson, a postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“It takes a lot of effort to cut down trees, particularly the biggest ones, so this just isn’t practical to do in large numbers.”
But Duncanson and her co-investigators, Ralph Dubayah and Oliver Rourke, both from the University of Maryland, found that this method tends to overestimate the height of large trees, leading to inflated biomass figures.
Instead of sampling trees by cutting them down, the new study used lidar, a laser-based technique that can analyse whole swaths of forest from above. The data were provided primarily by Goddard’s Lidar, Hyperspectral and Thermal instrument, known as G-LiHT.
The lidar data provide digital measurements of the height and crown radius – the average horizontal spread of the limbs – for every tree selected.
These measurements have been used to develop new mathematical models to estimate the biomass of the forests. The new figures suggest biomass has previously been overestimated by an average of 70%.
Bill Condie is a science journalist based in Adelaide, Australia.
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