Satellite images reveal which forests are dying before it's too late

Scientists have figured out how to read a forest's health from space. By measuring the light that bounces off leaves, researchers at the University of Notre Dame can now detect the early signs of forest decline—drought stress, disease, pest damage—before trees reach a crisis point.

The breakthrough centers on something called spectral reflectance: the specific wavelengths of light that leaf material reflects or absorbs. Different leaf compositions and conditions create different reflectance signatures. A healthy leaf reflects light differently than a stressed one. The insight is that these signatures correspond directly to gene expression—the cellular switches that turn on when a tree is struggling.

"By connecting reflectance with gene expression, we can get a real-time measure of forest health at the genomic level," says Nathan Swenson, who led the study. "We pick up the early indicators of declining forest health and connect them back to real changes happening on the cellular level."

The team tested this on sugar maples and red maples at their field site, measuring leaf reflectance and then analyzing genes related to water stress, drought response, photosynthesis, and plant-pest interactions. For more than half the genes they examined, they found a strong correlation: leaves expressing the same stress genes reflected the same wavelengths of light. The pattern held across different trees.

This matters because early detection is everything in forest management. Wildfires, droughts, and disease spread fastest through weakened ecosystems. Once a forest reaches crisis, intervention is expensive and often too late. But if you can spot trouble at the genomic level—before visible symptoms appear—you have time to act.

The potential scales dramatically. Satellites and sensors on the International Space Station already collect reflectance data for vast forest regions. Add artificial intelligence to process that data, and you could monitor entire forests at the genetic level. Swenson's team is now working to combine satellite imagery with AI to map tree species and gene expression profiles across whole ecosystems through the National Ecological Observatory Network.

"The end goal is using the right data to rapidly assess how trees are responding to stressors, so that we can intervene before the forest hits a crisis point," Swenson says.

This approach won't solve deforestation or climate change, but it shifts the timeline. Instead of discovering a forest is dying when it's already burning, land managers could know weeks or months earlier that intervention is needed. For ecosystems already under pressure, that head start matters.