First-ever map of height of all the world’s trees

In summer 2010, remote sensing expert Michael Lefsky created the first-ever map showing the height of all the world’s trees.

Michael Lefsky: The map consists of colored areas that indicate the height of those forests, from the relatively short forests of Northern Canada and Russia, and the evergreen temperate forests of the Pacific Northwest, which have some of our tallest forests, and then down into the tropical forests that are really relatively unknown, in terms of their height and canopy structure.

Dr. Lefsky said that taller the trees in a forest, the more carbon is stored in that forest. This map will help scientists figure out what places in the world are holding onto a lot of carbon.

Michael Lefsky: That’s important, because as forests are disturbed, we want to know how much carbon is going to be released from the stable storage within the forest as it’s eventually released to the atmosphere.

… that is, if those forests get cut down, how much carbon could be released into the air as carbon dioxide, one of the global warming gases. Dr. Lefsky used data from NASA’s ICESat orbital satellite, which reflected laser light from the ground and the tree tops to get their height. ICESat managed to give Lefsky just enough data to create the forest map before plunging into the Barents Sea on August 30, 2010. A research plane called IceBridge will continue some of the measurements made by IceSat until the launch of ICESat-2 in 2015. Dr. Lefsky talked about how he created the map.

Michael Lefsky: We combined data from two satellite systems, conventional images from the MODIS instrument, and estimates of forest height from the ICESat satellite to create a single image that gives you a height for all of the forested areas of the globe.

One of the big mysteries that Lefsky is trying to understand through mapping vegetation is that of the Earth’s “missing carbon.”

Michael Lefsky We have very good numbers, for instance, on the amount of carbon that’s being released to the burning of fossil fuels. We have very good numbers on the amount of carbon that’s being taken up by the ocean. When you tally up all the carbon that’s being released to or taken up from the atmosphere, you’re left with this missing carbon sink. We know that this carbon is in fact being absorbed by something in the system. But we don’t know where it’s going.

The ICESat mission ended in the summer of 2010, and Dr. Lefsky spoke on the continuation of its science.

Michael Lefsky: Although the ICESat mission has ended, in fact the science is going on. In fact, about one out of seven ICESat science papers that have been published are on forestry or terrestrial ecology related topics. And about a quarter of those have been published in the last two years. So there’s an awful lot of science that’s going on and will continue to go on as we analyze data from this mission. Currently, we’re looking toward the next generation missions. Those include ICESat-2, a follow on mission, and DESTINY, a mission that combines both a LIDAR and a RADAR, looking at both a biomass storage, forest height, as well as details of the Earth’s solid structure, so looking at earthquake prediction and mitigation and those sorts of issues.

Our thanks today to NASA’s ICESat Mission, improving our understanding of the effects of Earth’s changing climate.

September 13, 2010

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