Life hidden underground affects the success of forest management. Here's what happens
Half of the biodiversity of forests goes unnoticed because it lives underground. These organisms are tiny in size, but their importance to the ecosystem is enormous.
In a single teaspoon of forest soil there are thousands of species and billions of individual organisms. These include microorganisms such as bacteria and archaea, soil animals such as microscopic protozoa, nematodes, tardigrades, springtails and mites, and larger fauna such as millipedes, centipedes and worms.
A cubic centimeter of forest soil can also harbor more than a kilometer of fungal hyphae, the mass of thread-like cords that run through the soil and form mycelia.
This amazing diversity of subterranean life is organized into complex food webs, with many of the larger animals feeding on smaller animals and microorganisms. This complex network has been largely ignored in forest management, but could be a key ally in increasing the resilience of our forests in the face of global climate change.
Subway life
All subterranean life ultimately depends on plants for food. Some soil organisms feed on dead leaves and roots, converting them into organic matter. This matter is critical for soil fertility and water retention, and is the main store of soil carbon.
Other subterranean organisms depend on the simple sugars released by the roots of living trees to survive and grow. In tree needles and leaves, atmospheric carbon dioxide is converted to sugars and other metabolites through photosynthesis.
Up to half of the sugars produced in leaves are transported to tree roots. Some of these sugars are exuded from the root tips or transferred to mycorrhizal fungi that live in and around the roots.
The hyphae of mycorrhizal fungi extend from the root tips into the soil and also exude sugars and metabolites. These compounds support abundant soil microorganisms and form the basis of a vast subway food web.
Hours or days after carbon dioxide is absorbed by tree leaves, some of the carbon is released from roots and fungal hyphae and distributed through the subway food web.
Dead bodies and metabolites released by soil microorganisms are also an important source of organic matter.
Managing the whole forest
This new appreciation of the importance of living roots in supporting subway life should lead us to rethink forest management.
Logging cuts off the critical flow of subway resources, directly reducing the abundance and diversity of soil life. However, logging practices that conserve live trees within 50 feet of each other can maintain soil life throughout the logged area.
Logging practices that retain a portion of the live trees, such as continuous cover silviculture and retention silviculture, can help keep the soil alive in logged forests.
Retention silviculture in a Douglas-fir forest on Vancouver Island, where 40 live mature trees per hectare were retained.Image: Government of British Columbia, provided by the author.
Plant diversity is also important, as species differ in the variety of compounds released by their roots, which influences soil microbial diversity.
Soil biodiversity can be promoted by establishing forests with more than one tree species. In particular, forests containing broadleaf tree species and tree species with nitrogen-fixing microbial associates promote soil biodiversity and replenishment of soil organic matter.
Forestry in the 21st century
Faced with the twin crises of climate change and biodiversity collapse, we need diverse and resilient forests. Soil organisms are key allies in this endeavor.
Soil organisms provide half of the biodiversity in forests and regulate processes that govern soil fertility, water retention and greenhouse gas emissions. Forestry practices that promote soil biodiversity can contribute to making our forests resilient and diverse.
The vital role of living root inputs in maintaining soil organic matter and ground life has been recognized in agriculture and is a central tenet of regenerative agriculture, a set of practices that actively restore soil quality, biodiversity, ecosystem health and water quality while producing sufficient food of high nutritional quality.
Forestry could also be regenerative, especially if we apply practices such as continuous cover and species mixtures, and intentionally conserve ground life.
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