30 May

Map of the Week: The “Wood Wide Web”

By Nigel Jaffe

According to a report from the Earth Policy Institute, almost a third of the world’s land surface is covered by forests. Beneath every group of trees and plants stretch far-flung networks of roots, which are themselves interconnected by vast communities of fungi and bacteria. These underground structures, known as common mycorrhizal networks (or more colloquially, the “wood wide web”), play a vital role in communication between plants of a wide range of species.

Using a massive database comprising 1.2 million forest plots across more than 70 countries, scientists have created the first global map of the complex subterranean networks that make up the “wood wide web.” The international team of researchers, who published their work in the British journal Nature, represent ETH Zurich in Switzerland along with Stanford and Purdue in the United States. In order to construct the map, the group wrote a computer algorithm that analyzed Global Forest Initiative data to link certain varieties of fungus with corresponding areas of the globe.

In doing so, they took advantage of the fact that each of the 28,000 tree species in the database are associated with one of two types of microbe: ectomycorrhizal (EM) fungi and arbuscular mycorrhizae (AM) fungi. EM fungi are usually found in temperate and cooler climates, and are often linked with oak and pine trees. Conversely, AM fungi prefer warmer climates, such as the tropics, and can be found around the roots of maple and cedar trees. With these patterns in mind, the researchers were able to plot the distribution of the two types of fungus on the map using only data from tree populations.

The maps below depict the prevalence of EM and AM fungi worldwide. The figure on the left uses red highlights in areas where EM fungi are dominant and blue highlights in areas where EM fungi are scarce; meanwhile, the figure on the right takes the opposite approach, using red highlights in areas where AM fungi are dominant and blue highlights in areas where AM fungi are scarce.

The fungi examined here bear wider importance in the study of climate change on a global scale. Though these tightly-woven networks are over 500 million years old, they are just as vulnerable to today’s shifting temperatures as the forests they connect. The crucial issue at hand is the difference in how EM and AM fungi process atmospheric carbon: while EM fungi help to trap and store greenhouse gases, AM fungi instead promote carbon cycling, helping emissions disseminate into the atmosphere. While 60% of trees today are associated with EM fungi, as illustrated in the project’s maps, increasing global temperatures brought on by climate change could push EM fungi out of the top spot. The AM fungi, which are better suited to warm weather, may indeed take over as the prevalent variety globally, spelling trouble for the atmosphere and potentially contributing further to climate change on the highest geographic scale.

Sources: 1, 2, 3