It’s important to have accurate information on an area’s forest extent in order to properly protect forests and evaluate natural resources, conservation practices and environmental policies. But one of the challenges facing researchers is that the accuracy of remote sensing products varies widely. 

A group of researchers from the University of Delaware teamed up with an international group of collaborators to verify the accuracy of remote sensing products that measure forest extent. Together, they looked at forest extent estimates from seven land or tree cover remote sensing products and compared them to two independent forest inventory datasets.

Using the information, they developed a forest extent agreement map for Mexico that combined the information from the seven products and two datasets and identified the areas of agreement in their estimates.  

The National Aeronautics and Space Administration Carbon Monitoring System program of the United States funded the research, and the results of the study were recently published in Environmental Research Letters. 

Dustin Braden, who received his master’s degree from UD in 2023, was the lead author of the paper. Pinki Mondal, assistant professor in the Department of Geography and Spatial Sciences in UD’s College of Earth, Ocean and Environment, was a co-author on the paper. Mondal and Rodrigo Vargas, professor of ecosystem ecology and environmental change in UD’s College of Agriculture and Natural Resources and director of the Water Science and Policy program, co-advised Braden during his time at UD. 

Mexico’s forest surveys

Braden said that Mexico has one of the best programs in the world for gathering high-quality information about the country’s forests for the National Forest Inventory, which is run through Mexico’s Comisión Nacional Forestral (CONAFOR). 

The National Forest Inventory measures canopy density and the number of trees present, among other things, Braden said. For their research, Braden and his team accessed Mexico’s National Forest Inventory and compared it to the findings from various satellite products.

“Then, we could compare the two to see where there’s areas of agreement and disagreement to support better decision-making about the National Forest Inventories and these satellite-derived products,” Braden said.

It was the first time Braden had participated in a large international research project. With a background in conservation and geography, he also didn’t have much experience related to carbon monitoring. 

“One of the great things about being co-advised by both Pinki, who has more of the geographic information systems and remote sensing background, and Rodrigo, who has a little bit more of that carbon background, was getting to bring these two different fields together through my work and getting to learn how I could apply mapping and satellite data in a more specific way to ask really interesting questions,” Braden said. 

Forest extent agreements and disagreements

Using the data, the researchers were able to find areas where the satellite products agreed on forest extent and where they disagreed. They found that high agreement tended to occur in heavily forested areas like the Yucatan Peninsula and mountain areas in the Sierra Madre Oriental and Sierra Madre Occidental. High disagreement tended to occur in complex ecological zones like the tropical dry forest and subtropical mountain system, where the varied tree cover can lead to inconsistencies in remote sensing analysis.