John Upton/The Bay Citizen

A dead tree in a San Mateo forest killed by sudden oak death, which is caused by a close relative of fungus

Fungus-related plant diseases are wiping out forests across the world – and new research indicates a similar phenomenon emerged as a result of radical climate change some 250 million years ago. That in turn suggests that scourges such as sudden oak death, Dutch elm disease, and the collapse of eucalyptus stands in Australia could be linked to contemporary climate change.

These and other diseases attacking the world’s forests are caused by fungus, or by close relatives of fungus, and some scientists believe the fungi are seizing on tree weakness triggered by climate change and pollution. In a new paper published online Friday by the science journal Geology, UC Berkeley plant biologist Cindy Looy and fellow researchers based in England and the Netherlands argue that soil fungus played a major role in the disappearance of forests millions of years ago.

The prehistoric trees might have been weakened by rapid changes in the earth's climate at the end of the what's known as the Permian period, making them more vulnerable to fungus attacks, according to Looy.

“The plants that were still around were not doing well, and if plants are not doing well they’re much easier to attack by fungi,” Looy said. “Their defense system is down.”

Looy said it's impossible to rule out the possibility that future climate change will trigger similar devastation in forests across the world. Such an event, though, would be caused only by "really, really big" changes in the earth's climate.

"There were (other) big climate changes in the past, but we don’t have indications for fungal outbreaks at those times," Looy said.

The Permian period lasted roughly from 300 million years ago to 250 million years ago, when the greatest wave of extinctions in earth’s history coincided with a period of dramatic climate change.

During the Permian period, reptiles were evolving on a world dominated by a single mass of land, dubbed Pangea, which stretched from the North Pole to the South Pole. The period ended with a bang, when volcanoes spewed particles into the air that warmed the world and eroded the ozone layer, triggering the extinction of 90 percent of marine species and 70 percent of land animals. Other theories speculate that climate-changing belches of methane from deep beneath the earth's crust caused the cataclysm.

(In the wake of the biotic calamity, reptiles flourished and dinosaurs came to rule the world until they disappeared during a less dramatic wave of extinctions about 65 million years ago.)

Looy and her research partners investigated mysterious Permian-era fossils found around the world and concluded that they were a type of soil fungus. The fossil records suggest that the fungus became highly abundant at about the time that forests were disappearing.

The researchers published similar findings in the 1990s, but other scientists questioned their results, pointing out differences between the fossils and modern fungus. 

Looy said the new research suggests that the fossils resemble the resting phase of soil fungus, which has different traits than active fungus. Still, two other plant pathologists interviewed by the Bay Citizen expressed reservations about Looy's conclusions.

Ted Swiecki, a private industry plant pathologist, described the theory as "interesting" but said the telltale signs of fungus detected on the fossils do not necessarily mean that the fungus was deadly to trees.