Data from NASA has been used to create the first map that shows the height of forests around the world. This article from NASA’s earth science team lays out the implications for measuring the amount of carbon in the atmosphere and for studying carbon uptake by trees.

Scientific interest in the new map goes far beyond curiosities about tree height. The map has implications for an ongoing effort to estimate the amount of carbon tied up in Earth’s forests and for explaining what sops up 2 billion tons of “missing” carbon each year. Humans release about 7 billion tons of carbon annually, mostly in the form of carbon dioxide. Of that, 3 billion tons end up in the atmosphere and 2 billion tons in the ocean. It’s unclear where the last two billion tons of carbon go, though scientists suspect forests capture and store much of it as biomass through photosynthesis. There are hints that young forests absorb more carbon than older ones, as do wetter ones, and that large amounts of carbon end up in certain types of soil. But ecologists have only begun to pin down the details as they try to figure out whether the planet can continue to soak up so much of our annual carbon emissions and whether it will continue to do so as climate changes. “What we really want is a map of above-ground biomass, and the height map helps get us there,” said Richard Houghton, an expert in terrestrial ecosystem science and the deputy director of the Woods Hole Research Center. One of Lefsky’s colleagues, Sassan Saatchi of NASA’s Jet Propulsion Laboratory, has already started combining the height data with forest inventories to create biomass maps for tropical forests. Complete global inventories of biomass, when they exist, can improve climate models and guide policymakers on how to minimize the human impact on climate with carbon offsets.

The world’s tallest forests are found to be clustered in North America’s Pacific Northwest and areas of Southeast Asia. Shorter forests are found in Eurasia and Northern Canada. LIDAR laser technology measured forest canopy height by shooting pulses of light at the surface. Observing how much longer it takes for light to bounce back from the ground surface than from the top of the canopy yields the forest height. LIDAR can penetrate the top layer of forest canopy, providing a full snapshot of the vertical structure of the forest. It would have taken weeks of counting and measuring tree trunks in the field to yield the same data LIDAR can capture in seconds. The map was based “on data from more than 250 million laser pulses collected during a seven year period.” In order to then create the global map of forest height map, LIDAR data was combined with information from a satellite instrument called a Moderate Resolution Imaging Spectroradiometer (MODIS) that senses a much broader swath of Earth’s surface.

The next generation LIDAR measurements of forests  will improve the resolution of the map considerably. Those measurement “could come from NASA’s Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) satellite,” which is proposed for several years in the future.

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