Why Soil Is the Most Overlooked Ecosystem
Environmental conversations tend to happen at eye level. Forests, oceans, coral reefs, and polar ice are visible, photographable, and emotionally immediate. They receive significant attention, and rightly so.
The most biodiverse habitat on the planet may be none of these. It is the ground beneath your feet.
A single teaspoon of healthy soil can contain more living organisms than there are people on Earth. The FAO describes soils as among the most biodiverse systems on Earth, and a 2023 study estimated that soil may be home to approximately 59 percent of the species on Earth, making it a strong candidate for the most biodiverse singular habitat yet identified by researchers.
What Soil Actually Is
The word soil tends to conjure dirt. Something to wash off, to avoid tracking inside, to fill a pot with. That framing obscures almost everything important about it.
Healthy soil is a living system. It contains an enormous diversity of organisms, from bacteria and fungi to protozoa, nematodes, insects, and other invertebrates. These communities are not incidental to the soil. They are the soil, in the sense that their activity is what makes it function.
Certain soil microorganisms convert atmospheric nitrogen into forms that plants can use, making nitrogen available for plant growth in ecosystems where biological nitrogen fixation occurs. Mycorrhizal fungi form extensive networks around and within plant roots, helping plants access nutrients and, in some systems, facilitating the movement of resources through the soil. Earthworms aerate the soil and break down organic matter into forms that microorganisms can process. Protozoa regulate bacterial populations and release nutrients through their activity.
Remove any significant portion of this community and the system begins to fail. Plants struggle to absorb nutrients. Organic matter accumulates rather than cycling. The soil itself loses structure, water retention, and the capacity to support life above it.
The Carbon Connection
Soil stores more carbon than the atmosphere and terrestrial vegetation combined, making it one of Earth's most important carbon reservoirs. This is not a passive process. It depends on the activity of soil organisms decomposing organic matter, building fungal networks, and stabilising carbon in forms that remain in the ground rather than entering the atmosphere.
When soil is degraded, that carbon storage capacity is reduced. Degraded soil also loses its ability to retain water, resist erosion, and support the plant communities above it.
The FAO estimates that approximately 95 percent of the food we eat is produced directly or indirectly from soils. Food production depends on healthy soil, and healthy soil depends on the living communities within it remaining functional.
What Damages It and What Helps
Compaction, erosion, loss of organic matter, pollution, nutrient imbalance, and some intensive land management practices can degrade soil health over time. These pressures are well documented in agricultural science. Less discussed is the role of household and garden choices in either contributing to or supporting soil health at a local level.
Composting returns organic matter to the soil in a form that microorganisms can process and incorporate. It closes the loop between food waste, microbial activity, and plant nutrition. Adding mature compost can increase soil organic matter, support soil biological activity, and improve properties such as nutrient cycling and water retention.
Avoiding unnecessary compaction, mulching to protect soil surface organisms from temperature extremes, and choosing plants with deeper root systems all help maintain the living community underground. None of these require significant resources or expertise. They require a shift in how you think about what the garden floor actually is.
The Ecosystem You Cannot See
There is something disorienting about the idea that the most biodiverse habitat on Earth may be directly beneath wherever you are standing right now. Not in a remote jungle or deep ocean trench. Underfoot, in the garden, in the park, in the field outside town.
The insects and birds that attract conservation attention depend, ultimately, on the health of the soil below the plants they inhabit. The food chain starts underground. Everything visible above it is downstream.
Paying attention to what happens below the surface is not a specialist concern. It is the foundation of almost everything else.
Sources and Further Reading
• Food and Agriculture Organization of the United Nations (FAO)
• PLOS Biology
• United States Department of Agriculture (USDA)
• Nature Reviews Earth & Environment
• European Commission Joint Research Centre (JRC)
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