In and around the tangled roots of the forest floor, fungi and bacteria grow with trees, exchanging nutrients for carbon in a vast, global marketplace. A new effort to map the most abundant of these symbiotic relationships – involving more than 1.1 million forest sites and 28,000 tree species – has revealed factors that determine where different types of symbionts will flourish.

Watercolor depicting the global connections between forests, microbes and Earth

Forests and microbes are symbiotically connected globally. (Image credit: Sora Hasler)

The work could help scientists understand how symbiotic partnerships structure the world’s forests and how they could be affected by a warming climate.

Stanford University researchers worked alongside a team of over 200 scientists to generate these maps, published May 15 in Nature. From the work, they revealed a new biological rule, which the team named Read’s Rule after pioneer in symbiosis research Sir David Read.

In one example of how they could apply this research, the group used their map to predict how symbioses might change by 2070 if carbon emissions continue unabated. This scenario resulted in a 10 percent reduction in the biomass of tree species that associate with a type of fungi found primarily in cooler regions. The researchers cautioned that such a loss could lead to more carbon in the atmosphere because these fungi tend to increase the amount of carbon stored in soil.

“There’s only so many different symbiotic types and we’re showing that they obey clear rules,” said Brian Steidinger, a postdoctoral researcher at Stanford and lead author of the paper. “Our models predict massive changes to the symbiotic state of the world’s forests – changes that could affect the kind of climate your grandchildren are going to live in.”