Forests: Why are 'belowground ecosystems' so important?

Trees get all the credit. But for a forest, the belowground ecosystem—soil, roots, fungi, and microorganisms—is equally important.

Traditionally, the aboveground ecosystem has been studied more often. According to researcher Whitney Stohr, “Aboveground organisms, tree stands, and the forest floor are immediately identifiable components of a forest ecosystem; one does not typically refer belowground when describing a forest in common parlance.” That’s because “belowground remains, physically and hence metaphorically, out of sight, out of mind.”

Healthy forests are important for a healthy future, and a healthy future begins belowground. Forests account for 70 percent of terrestrial biodiversity, and most of it is found belowground. Furthermore, the majority of a forest’s carbon storage and sequestration, essential for mitigating climate change, happens belowground.

When it comes to forest ecosystem services, or natural benefits, trees often come to mind first: they provide aesthetics, air and water filtration, and habitat. But many of these processes begin belowground. Forests account for 25 percent of the world’s biomass, and the fine root systems of trees are responsible for 75 percent of forest biomass production. This organic matter is essential to soil health and acts as a food source for many different species.

Belowground ecosystems are not just a food source, they are an essential habitat, too. Fifty percent of animal biodiversity is found belowground. The ecosystem below includes bacteria, fungi, and nematodes, to name a few. These often-forgotten ecosystems are more diverse than the aboveground, and these species are responsible for many ecosystems that plants, animals, and humans rely on, including water purification, soil health, and decomposition.

Both nutrient cycling and carbon storage take root in the soil. Nutrient cycling—including the nitrogen cycle and the carbon cycle—largely takes place belowground. These processes influence water health, plant growth, and the sequestration of greenhouse gases. Beyond forests, belowground health strongly influences food production.

Many recent studies have sought to examine how the aboveground and belowground ecosystems interact. Those studies may indicate that when one part of the ecosystem is out of balance, the other will be, too. Stohr gives the example of forest conversion. Converting forests to agriculture can decrease plant diversity and impact nutrient cycling, which in turn affects the food web and biomass inputs into the ecosystem.

Stohr proposes several avenues to bring greater awareness to the belowground. First, more research funding can expand our current knowledge of these ecosystems and why they matter. This can lead to policies that protect the entire forest ecosystem, not just the trees. Stohr concludes, “Effective decision making at the scientific, policy and global level can increase current focus on belowground ecosystems and positively advance scientific research and available funding for ecological restoration of the complete forest environment.”