What the West’s trees tell us

How can biomass and carbon data help us mitigate the effects of human activity?


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Every tree tells part of the story of Earth and its atmosphere, from the planet’s available carbon and oxygen to its soil and water health. Tree height and forest undergrowth help scientists study biodiversity and predict wildfires, while the location and density of growth are linked to hydrology and erosion in mountainous regions. Scientists have long studied these patterns, but until five years ago, there was no comprehensive way to keep track of them. Instead, scientific understanding was piecemeal and regional. In 2011, Wayne Walker and Josef Kellndorfer from the Woods Hole Research Center mapped every forest in the United States, along with its biomass and the carbon it stores, using satellite and ground data collected by the U.S. Forest Service, NASA and the U.S. Geological Survey from 1999 to 2002, to create a forest biomass map in more precise detail than any other made. The darker the spot, the denser, taller and more robust the forests are. Predictable trends emerge: The rich forests of the Pacific Northwest and Northern California are obvious, for example. But there were also surprising insights, like the grid-like patterns created by human development in other Western forests. The map is already helping public-lands agencies and academics study and manage forest restoration, but researchers are working to update it: Western forests are changing rapidly due to logging, climate change and tree disease. “It’s more valuable to understand how the forest is changing over time, in terms of ability to store carbon,” Walker says. For now, land managers rely on these pixelated swaths of green as their baseline for understanding our country’s forests and their future.