UMD Researchers Map 35 Years of Global Land Surface Transformation

Geographical Sciences researchers find overall global tree cover increased but rainforests suffered between 1982-2016

Analyzing 35 years worth of satellite images, researchers from the University of Maryland (UMD) Department of Geographical Sciences paint a comprehensive picture of how the Earth’s land surfaces have transformed throughout time. The research, published August 8 in Nature, is the first to map changes to global land cover over an extensive period from 1982 through 2016.

The researchers utilized satellite data to monitor changes in tall vegetation, such as trees, as well as short vegetation and bare ground throughout the world. Surprisingly, they discovered that global tree cover has increased by more than 7 percent overall since 1982. However, tropical rainforest regions saw a net loss in tree cover.

“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.

By drilling through the satellite images to focus on specific areas of the globe, researchers were able to view the long-term effects of land changes at regional levels. For instance, forests in the Western United States are suffering increasing stress from insects, wildfires, heat and drought due to regional warming. Meanwhile, in the temperature-limited Arctic, warming is facilitating wood vegetation growth in northeastern Siberia, western Alaska and northern Quebec. The researchers also discovered that bare ground cover decreased by more than 3 percent worldwide in this 35-year period, most notably in regions of Asia where agricultural practices have been improved and modernized over the last several decades.

“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 policy-makers can use our results to make informed decisions about future land use.”

The UMD researchers hope their findings can improve modeling of land use changes around the world, advance understanding of environmental change and aid in building a long-term record of how humans are impacting the planet.

“The results of this study reflect a human-dominated Earth system,” said Hansen. “Direct human action on landscapes is found over large areas on every continent, from intensification and extensification of agriculture to increases in forestry and urban land uses, with implications for the maintenance of ecosystem services worldwide.”

In addition to Song and Hansen, the research team 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.

This article was originally published August 9, 2018.

Published on Thu, Aug 9, 2018 - 10:00AM