The Path of Least Resistance

Thinley Wangden ’23 uses NASA data to map safe corridors for Bhutan’s elephants

By Linzy Rosen ’22
May 13, 2021

Dense forests bulldozed. Homes, roads, and buildings developed. Habitats lost. Add elephant attacks and poaching to the mix, and the survival of the remaining 678 Asian elephants in southern Bhutan hangs in the balance.

Spurred to action, Thinley Wangden ’23 joined a team at NASA and helped map a path forward by identifying better biological corridors, or natural passages, to protect Bhutan’s residents and its elephants, ecologically, culturally, and religiously important to the small country.

As a NASA intern, the Bhutanese native gathered and interpreted NASA Earth observations data to advise premier conservation organizations, including the Bhutan Tiger Center, Bhutan Foundation, and the Bhutan Ecological Society. Her results will contribute to the development of new strategic corridors for the elephants and inform future land policies.

2021Spring_SouthernBhutan_Corridor Suitability: Map comparing the elephant movement corridor suitability map displaying least-cost paths to existing corridors in southern Bhutan.
Overlaying data on top of a NASA satellite map, researchers have marked southern Bhutan’s existing wildlife corridors and new, least-cost paths that are potentially favorable for elephant movement.

During the spring 2021 semester, Wangden, along with four other Bhutanese undergraduate and graduate students, was selected to participate in a three-term project under the NASA DEVELOP program. While corridor mapping was new to Wangden, she was drawn to the opportunity to work on a large-scale project, NASA’s Southern Bhutan Ecological Forecasting II project.

Bhutan’s Asian elephants are keystone wildlife species that occupy the country’s numerous protected parks. They also roam in search of food and water, sometimes using wildlife corridors to get from park to park. Those corridors, however, were created for Bhutan’s tiger population and pass through habitats not suitable for elephants. As a result, elephants search for their own pathways in an environment experiencing habitat loss and often wander too close to human settlements.

The end result? Human and elephant deaths as well as village destruction. To address this, Wangden suggested new corridors by linking habitats that pass through the most suitable land for elephants to potentially minimize human conflicts.

“With the linkages,” Wangden said, “we’re showing paths that would accumulate the least resistance,” or be more favorable to elephants.

Thinley Wangden
Thinley Wangden ’23

NASA researchers and interns had previously determined that land suitability, or amount of resistance, could be measured by nine different variables, including elevation, precipitation, and distance to food and water sources, among others. High resistance would include areas without easy access to food or water or with unsuitable terrain, Wangden said.

Accessing NASA satellite data, Wangden’s team used Linkage Mapper software to generate new corridors with low resistance. To link habitats that have the most suitable conditions for a new corridor, the team first had to invert an elephant land-suitability model. Instead of thinking of how suitable an area was, they had to calculate how unfavorable it was. Linkage Mapper then computed the “costs” of connecting the different protected parks and presented Wangden’s team the paths with the least “cost,” or level of resistance, Wangden said. This allowed them to highlight the linked areas that had the least resistance.

Another aspect of the internship involved creating land-cover maps for the years 2010 and 2015 using NASA satellite images to classify the areas as either mature forests, immature forests, cultivated land, water, or barren land. They then performed accuracy assessment tests in GIS software, Wangden said, to ensure the results were as robust as possible.

These maps, said Wangden, will be used in the next phase of the project to forecast land cover in 2030 and predict changes to elephant habitat. More linkages can then be developed using those forecasts.

2021Spring_SouthernBhutan_LUCLMap: 2015 land use land cover classification map at the Bhutan-India border.
This NASA 2015 land-use map shows land-cover classifications at the Bhutan-India border.

This spring Wangden presented her results to the project’s partners. The corridor data, Wangden said, were well received by the scientists and wildlife experts from these groups.

“It just feels very rewarding to know that our results are actually going to be used to implement something on a wider scale in real life,” she said.

In addition to helping organizations develop new corridors and predict land cover, her work can also be used to address climate change. “Bhutan, in general, has been seeing the effects of climate change,” said Wangden. Loss of habitat, especially, has forced and driven elephants into the urban settlements.

This is precisely what her team’s results confirmed. “One of the most important aspects from our corridor mapping,” said Wangden, “was that a potential suitable corridor runs near a current human settlement where a lot of human-elephant conflicts have been recorded.”

This unofficial corridor is currently being used by elephants due to its hospitable terrain, but it’s leading them too close to humans. Wangden’s data helps to explain why certain clusters of human-elephant conflicts are occurring, and these results can be used to determine better paths forward—as conservation groups race against the extinction clock.

Though Colby is more than 7,000 miles away from Bhutan’s remaining forests, Wangden’s contributions will bolster new corridor and elephant management plans—before it’s too late.