Fungus-infected forests heat the planet

By John Upton

Forests suck carbon dioxide out of the air. They use solar energy to combine the carbon dioxide with water droplets to form sugars that fuel plant growth. During that chemical reaction, known as photosynthesis, waste oxygen is released back into the air.

So the effects of widespread deforestation by lumberjacks and bulldozers are relatively easy to understand. Less forests means more carbon dioxide, which heats the planet, and less oxygen for us to breathe.

New research has revealed that deforestation can take an even more sinister turn when it’s performed by a fungus. Fungal pathogens and fungus-like diseases are stealthily felling forests across the world. Forests at Big Sur disappeared in less than a decade after sudden oak death moved onto their turf. Cypress canker, native to California, is destroying trees across Europe. Dutch elm disease has forever changed the landscape on the East Coast.

Trees in Yale Myers Forest, CT, may look healthy, but many are rotting from the inside. Heart rot fungus breaks down the wood into substances that are consumed by bacteria, which further break the material down into methane. / Flickr: morrowlong

These symptoms of a sick planet do more than merely strip the earth of some of its greatest carbon sponges. Scientists have discovered that fungus disease can cause some of the wood in infected trees to break down not into carbon dioxide (CO2), but to break down anaerobically with the assistance of bacteria into methane (CH4), which is a far more potent and damaging greenhouse gas.

The university researchers measured methane levels in Connecticut woodlands infected by heart rot, a fungus disease, and reported in the journal Geophysical Research Letters that concentrations were so high in some places that it was flammable. Methane concentration in the air is normally less than 2 parts per million, but the researchers discovered levels in some trees that reached more than 160,000 parts per million. The average methane concentration in the forest was 15,000 parts per million.

The ailing forest was releasing enough methane to counteract the climate-cooling benefits of nearly one-fifth of the carbon dioxide it was absorbing, researchers calculated.

The researchers point out that their study covered just one forest, and one type of fungus disease. This particular disease is unique in that the trees often appear outwardly healthy while they rot away from the inside. But they warn that other fungal diseases that are laying waste to woodlands around the world could have similar effects.

“I think it’s fair to say that wood-rotting fungi in general could lead to this effect,” lead researcher Kristofer Covey, a Ph.D. candidate at Yale University’s School of Forestry, told me. “It’s hard to say if more aggressive fungal pathogens could lead to further emissions or not.”

Now is a terrible time to be losing forests. They are needed to help soak up all the carbon we’re pumping into the atmosphere when we burn fossil fuels. So this discovery comes as a double-whammy: Not only are we losing carbon-storing forests to fungus, but the fungi are taking carbon that had been stored in the trees and helping to turn it into a particularly potent greenhouse gas that further accelerates the rate of climate change.

The discovery offers one more reason to protect our forests from fungus diseases. Unfortunately, the problem has become so rampant that there is very little that we can do about it.