His research is in the area of human-environment interactions in land systems. He develops integrated approaches to study land use change by linking remote sensing and socio-economic data. This includes research to better detect subtle land changes based on time series of Earth observation satellites at multiple scales. He aims to improve modeling causes and impacts of forest-cover changes, dryland degradation, and agricultural intensification. He focuses on land use transitions — i.e., the shift from deforestation (or land degradation) to reforestation (or land sparing for nature) that is taking place in some forested countries or drylands.
He was chair of the international scientific project, Land Use and Land Cover Change (IGBP/IHDP LUCC), from 1999 to 2005. In addition, he contributed to the Millennium Ecosystem Assessment.