Learning our forests from space– mapping deforestation and regrowth

global deforestation 2000-2012 map
Using Landsat imagery and cloud computing, researchers mapped forest cover worldwide as well as forest loss and gain. Over 12 years, 888,000 square miles (2.3 million square kilometers) of forest were lost, and 309,000 square miles (800,000 square kilometers) regrew. / Image : NASA Goddard, based on data from Hansen et al., 2013.

Laura Nielsen for Frontier Scientists

“Every day, Landsat satellites provide essential information for land managers and policy makers to support wise decisions about our resources and environment in the places we live and work.” (NASA)

Matthew Hansen, University of Maryland, and co-author Thomas Loveland, U.S. Geological Survey, released an unprecedented record of global deforestation and forest regrowth from 2000 to 2012. Their maps and findings were published in the journalScience in November 2013. The undertaking was made possible by the NASA / USGS Landsat 7 satellite, and the freely available Landsat Archives. The capability to see forest changes on a local-to-global scale allows scientists and forest managers to make better-informed decisions. Anne Castle, Assistant Secretary of the Interior for Water and Science, said “Tracking changes in the world’s forests is critical because forests have direct impacts on local and national economies, on climate and local weather, and on wildlife and clean water.”

The earth-observing Landsat 7 uses an instrument called the Enhanced Thematic Mapper Plus (ETM+) to record images of Earth. Landsat images have 30-meter resolution, meaning each pixel represents an area about the size of a baseball diamond. Landsat 7 orbits the Earth once very 99 minutes, and every 16 days (233 orbits) it returns to image the same location. That gives scientists a thorough and consistent high-resolution record of Earth’s surface.

Hansen’s study discovered that from 2000 to 2012 global forests lost 888,000 square miles [2.3 million square kilometers] and gained 309,000 square miles [800,00 square kilometers]. The USGS news release compares this to losing forested land the size of all U.S. states east of the Mississippi River, then gaining back Texas and Louisiana.

tornado path deforestation
The forest cover maps also capture natural disturbances such as this 2011 tornado path in Alabama. In this map, the colors represent forest loss by year, with yellows representing loss closer to 2000 and reds representing later forest loss, up to 2012. / Image: NASA Goddard, based on data from Hansen et al., 2013.

Important resource records like this one would not be possible without freely available Landsat data, or the cloud computing power of the Google Earth Engine.

The maps paint a picture of our ever-changing planet. Tree farms in the southern United States harvest and replant their crops. In the Southern Hemisphere, Brazil has halved their staggering deforestation rate, but other nations are increasingly felling rainforests. And to the north, Russia’s expansive forests lost the most ground of any nation’s. Human activity is the greatest cause of deforestation, but other forces like wildfire, insects, and storms also make an impact. Climate change also alters growing conditions, and is shifting the ideal growing range for many tree species further and further away from the hot equator.

Forests face many challenges. They are important not only as the pillars of many ecosystems, but also as carbon sinks… taking carbon dioxide (CO2) out of the atmosphere and releasing oxygen. Understanding forest gains and losses helps us understand the bigger picture.

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  • ‘Changes in World’s Forests Portrayed in High Definition’ USGS Newsroom (2013)
  • ‘High-Resolution Global Maps of 21st-Century Forest Cover Change’ Hanset et al., Science (2013)
  • ‘NASA-USGS Landsat Data Yield Best View to Date of Global Forest Losses, Gains’ Kate Ramsayer for NASA Goddard (2013)