Dense rainforests, maple-blanketed mountains and sweeping coniferous forests demonstrate the growth and proliferation of trees adapted to specific conditions. The regional dominance of tree species we see on the surface now, however, might actually have been determined underground long ago.

Princeton researchers report that the organization of forests worldwide — such as conifers in northern boreal forests or the broad-leafed trees of the tropics — are based on the ancient relationships that plant species forged with soil-dwelling microbes such as fungi and bacteria. These tiny organisms, known as symbionts, enhance the roots’ uptake of the crucial nutrients nitrogen and phosphorus.

The researchers reported in the journal Nature Ecology and Evolution that trees and shrubs came to dominate specific biomes by evolving the most competitive arrangement with local soil microbes — and cutting competing plants out of the action.

The biome-specific dynamics between plants and soil microbes could help scientists understand how ecosystems may shift as climate change brings about warmer temperatures that alter the interplay between trees, microbes and soil.

Because the most competitive symbiotic arrangements for a particular biome triumph, scientists would only need to understand how an ecosystem is changing to gauge which vegetation will be moving in and which will be moving out.