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Science

Map Depicts Global Forest Heights

A first of its kind map has been created detailing the height of the world’s forests.

There are other local- and regional-scale forest canopy maps that exist, but this new map is the first of its kind that spans the entire globe based on one uniform method.

Such a map has benefits for climate scientists looking to determine how much carbon is stored in our planet, improving climate models and guiding policy makers, as well as shorter term implications such as predicting the spread and behaviour of fires.

But according to the author of the map, Michael Lefsky, the remote sensing specialist from Colorado State University, “this is really just a first draft, and it will certainly be refined in the future.”

Lefsky used data from a laser technology that is capable of capturing vertical slices of surface features by shooting pulses of light at the surface and observing how much longer it takes for the light to bounce back from the ground surface than from the top of the canopy. However this method was only able to capture 2.4% of the planet’s forested surfaces, so Lefsky completed the map by combining his LIDAR data with information from the the Moderate Resolution Imaging Spectroradiometer (MODIS), a satellite instrument aboard both NASA’s Terra and Aqua satellites that senses a much broader swath of Earth’s surface.

The height map is one part in an effort to understand how much carbon is tied up in the biomass of our forests. “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.

Humans release about 7 billion tonnes of carbon annually. Of that, 3 billion tonnes ends up in the atmosphere and another 2 billion tonnes makes its way into the oceans. However the remaining 2 billion tonnes of carbon is currently missing, though scientists do suspect that it is captured by forests and stored as biomass through photosynthesis.

But so little is known about our forests and their role in the carbon cycle, and this map could help begin to shed light on the issue.

The results of the map are interesting in and of themselves though. The tallest forests were clustered in the Pacific Northwest of North America and portions of Southeast Asia. Shorter forests are found in large swathes across northern Canada and Eurasia. Temperature conifer forests have the tallest canopies, easily measuring above 40 metres (131 feet) while boreal forests typically have canopies less than 20 metres (65 feet) in height.

Source: NASA/Goddard Space Flight Centre

Image Source: NASA Earth Observatory/Image by Jesse Allen and Robert Simmon/Based on data from Michael Lefsky




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