Forests in the Peruvian Amazon aren't growing back after gold mining — not just because the soil is damaged from toxic metals, but because the land has been depleted of its water. A common mining method known as suction mining reshapes the terrain in ways that drain moisture and trap heat, creating harsh conditions where even replanted seedlings can't survive.
The findings , published in Communications Earth & Environment, revealed why reforestation efforts in the region have struggled. One of the study's co-authors is Josh West , professor of Earth sciences and environmental studies at the USC Dornsife College of Letters, Arts and Sciences.
"We've known that soil degradation slows forest recovery," said West, who is a National Geographic Explorer . "But this is different. The mining process dries out the land, making it inhospitable for new trees."
Mapping a damaged Amazon landscape
The research team was led by Abra Atwood , a scientist at the Woodwell Climate Research Center and a former student of West, who earned her doctorate at USC Dornsife in 2023. Working with colleagues from Columbia University, Arizona State University and Peru's Universidad Nacional de San Antonio Abad del Cusco, the team studied two abandoned gold mining sites in Peru's Madre de Dios region , near the borders of Brazil and Bolivia.
They used drones, soil sensors and underground imaging to understand how suction mining reshapes the land. The technique, commonly used by small-scale and often family-run operations, blasts apart soil with high-pressure water cannons. The loosened sediment is funneled through sluices that filter out gold particles, while lighter material, including nutrient-rich topsoil, washes away. What remains are stagnant ponds — some as large as football fields — and towering sand piles up to 30 feet high.
Unlike excavation mining, which is used in other parts of the Amazon and can preserve some topsoil, suction mining leaves little behind to support new growth.
To measure soil moisture and structure, the researchers used electrical resistivity imaging, a technique that tracks how easily moisture moves through soil. They found that the sand piles act like sieves. Rainwater drains through them up to 100 times faster than in undisturbed soil. These areas also dry out nearly five times faster after rain, leaving little moisture available for new roots.
To compare conditions, the team installed sensors in various locations — sandy and clay soils, pond edges and undisturbed forests — and found that deforested sites were consistently hotter and drier. On exposed sand piles, surface temperatures reached as high as 145 F (60°C).
"It's like trying to grow a tree in an oven," West said.
Drone-mounted thermal cameras showed how barren ground baked under the sun while nearby forested areas and pond edges stayed significantly cooler.
"When roots can't find water and surface temperatures are scorching, even replanted seedlings just die," said Atwood. "It's a big part of why regeneration is so slow."
Saving the Amazon with better practices
Although the team observed some regrowth near pond edges and in low-lying areas, large swaths of land remained bare, especially where sand piles are widespread. These spots, which are farther from the water table and lose moisture quickly, are harder to reforest.
Between 1980 and 2017, small-scale gold mining destroyed more than 95,000 hectares — an area more than seven times the size of San Francisco — of rainforest in the Madre de Dios region. In and around the Tambopata National Reserve, operations continue to expand, threatening both biodiversity and Indigenous lands. Across the Amazon, gold mining now accounts for nearly 10% of deforestation.
The researchers suggest that recovery efforts could benefit from reshaping the terrain itself. Flattening the mining sand piles and filling in abandoned ponds could bring tree roots closer to groundwater, improving moisture retention and boosting regrowth. While natural erosion may eventually do the same, the process is far too slow to meet urgent reforestation needs.
"There's only one Amazon rainforest," West said. "It's a living system unlike anything else on Earth. If we lose it, we lose something irreplaceable."
About the research
In addition to Josh West, Shreya Ramesh and Chan-Mao Chen at the USC Dornsife College of Letters, Arts and Sciences, study co-authors include Abra Atwood of the Woodwell Climate Research Center; Jennifer Angel Amaya of the Lamont-Doherty Earth Observatory at Columbia University; Hinsby Cadillo-Quiroz of Arizona State University; and Daxs Coayla of the Universidad Nacional de San Antonio Abad del Cusco in Peru.
This research was supported by the National Geographic and Rolex Perpetual Planet Amazon Expedition .
