Analyzing 35 years of satellite images, researchers from the UMD Department of Geographical Sciences have discovered that while global tree cover has increased by more than 7 percent overall since 1982, tropical rainforest regions saw a net loss.

The resulting paper, published yesterday in Nature, is the first to map changes to global land cover over an extensive period from 1982 through 2016. Researchers utilized satellite data to monitor changes in tall vegetation, such as trees, as well as short vegetation and bare ground throughout the world.

“It’s important to understand that the trees we’re gaining are not in rainforests” said Matt Hansen, professor of geographical sciences and a co-author on the study. “While we saw an increase in tree cover in higher altitudes outside of the tropics, tropical deforestation continues and so do the harmful carbon emissions that result from it.”

To understand the drivers of global land change, Hansen and colleagues used a probability sample and interpretation of very high-resolution images in Google Earth, which allowed them to see fine details of land use such as buildings, crop fields, logging roads, grazing paddocks and oil wells. They attributed 60 percent of all land changes occurring over this 35-year period to direct human activities, and say the other 40 percent were caused by indirect drivers such as climate change.

Other findings include that forests in the western United States are suffering increasing stress from insects, wildfires, heat and drought; warming is facilitating wood vegetation growth in northeastern Siberia, western Alaska and northern Quebec; and bare ground cover decreased by more than 3 percent, most notably in regions of Asia where agricultural practices have improved and modernized.

“The study really shows the complexity of land change at regional scales,” said lead author Xiao-Peng Song, a post-doctoral associate in the UMD Department of Geographical Sciences. “We hope that experts who specialize in specific regions can use our dataset to investigate the exact drivers of land change and that policymakers can use our results to make informed decisions about future land use.”

The research team also included Associate Research Professor Peter Potapov, Research Professor John Townshend and post-doctoral associate Alexandra Tyukavina from the UMD Department of Geographical Sciences, as well as Stephen Stehman from the State University of New York and Eric Vermote from NASA Goddard Space Flight Center.