Satellites can judge forest health

Our forests’ health can now be gauged from space, thanks to colour changes caused by underground fungi.

The symbiotic relationship between underground fungi and trees is based on a sort of forest barter system: trees give fungi sugars, and the fungi spread their networks through the soil to help gather nutrients and water for the trees.

Now, researchers from NASA and the University of California, Los Angeles have developed a way to monitor these relationships using satellites, which could help see shifts in regional forest health during climate change.

Interactions between trees and fungi can also provide insight into a tree’s general access to nutrients. This means the new research gives researchers an easy method of monitoring the overall health of the world’s forests over long periods.

The mapping systems, interestingly, come down to colour: two particular types of underground fungi have a profound impact on the colours broadcast by trees. These colour changes are significant enough to be viewed from satellite images.

“Every tree species has a distinct spectral signal, a kind of measurable aura,” explains Sean McMahon, at the Smithsonian Forest Global Earth Observatory (ForestGEO) network.

“Now we can tell who their underground friends are, an indicator of their nutrient status, from the sky.”

To make the discovery, researchers compared traditional data with the satellite images of 130,000 individual trees in three different forest locations across the US.

Using colour data from satellite images, researchers were able to figure out how much the trees were interacting with both ectomycorrhizal fungi, which only grows on and around root cells, and arbuscular mycorrhizal fungi, which penetrates cells.

Interactions with each species indicate more complex traits in trees. For instance, arbuscular mycorrhizal-associated trees usually cycle their nutrients at a faster rate than those that associate with ectomycorrhizal fungi.

Manually mapping these interactions with fungi for every single tree across entire countries would be an impossible task.

The ForestGEO network uses a series of 63 different plots to collect detailed data on the world’s forests over long periods.

The researchers aim to repeat the process across more of the ForestGEO network’s plots in the near future, with the hope that comparisons will lead to deeper understanding of the effects of climate change, pollution and deforestation on the world’s forests.

They published their work in Global Change Biology.