Soil Biodiversity

What Is It?

Scientists have long debated what counts as “life in the soil.” It’s a surprisingly complex question.

Should we include only organisms that spend their entire lives underground? Or also those that live on the surface, pass through the soil during part of their life (like larvae), form close partnerships with underground creatures (like helpful microbes), or exist as invisible but active agents (like bacteria and viruses)?

The United Nations Convention on Biodiversity offers a broad and inclusive definition: “the variation in soil life, from genes to communities, and the ecological complexes of which they are part, that is from soil micro-habitats to landscapes.” In other words, soil biodiversity includes everything from bacteria and fungi to nematodes, insects, worms, spiders, mollusks, plants, and even burrowing mammals. Viruses pose a unique challenge – they don’t reproduce independently and have unusual genetic properties – so many surveys leave them out, even though they’re known to be present in soil ecosystems.

How Much Is There?

Until recently, there was only one major attempt to estimate how much of Earth’s life actually lives in the soil – and that study looked only at animals. In 2023, a broader study by Anthony, Bender, and van der Heijden estimated that soil is home to roughly 59% of all species on Earth (plus or minus 15%), again excluding viruses.

Some families are especially suited to dwelling in the soil:

• Enchytraeidae, small worm-like creatures: 98.6% of species live in the soil
• Fungi: 90%
• Land plants (Plantae): 85.5%
• Termites (Isoptera): 84.2%

This underscores just how much of life is hidden beneath our feet.

Why Is It Important?

What happens aboveground has a direct impact below ground – and vice versa. The soil food web is the network of organisms that break down organic matter and recycle nutrients, making them available to plants and other organisms. Because of this web, a healthy soil ecosystem supports agriculture, forests, and water quality – and helps us adapt to the challenges of increasingly extreme climates.

Soil biodiversity also plays a role in suppressing harmful microorganisms, including those that cause diseases like anthrax, tetanus, and botulism. It’s also key to producing clean air, clean water, and nutritious food. In short: soil life is essential to human life.

How Is It Doing?

Today, about 75% of Earth’s land has been significantly altered by human activity. Deforestation, intensive farming, and paving over land with roads and buildings all change the structure and function of soil ecosystems. Other pressures – like pollution, climate change, acid rain, and invasive species– further threaten soil health.

Our understanding of the full range of soil organisms is still limited, which makes it hard to measure the full impact of these changes. But we do know that certain activities – like industrial agriculture – can damage soil structure, reduce its ability to hold water, and kill beneficial organisms like worms and fungi. Chemical fertilizers and pesticides often favor bacteria over fungi, creating an imbalance in microbial communities.

Climate change adds more stress, with rising temperatures, extreme drought and flood events, and increased CO₂ itself all affecting life in the soil in complex ways. New threats like waste pharmaceuticals and microplastics are just beginning to be studied.

What Can We Do?

Reduce paved surfaces where possible, and replace them with native plantings.

Restore plant diversity. Remove invasive plants and lawn grass, and replace them with a variety of native species suited to your area. These native plants evolved alongside local soil organisms and help support healthy underground ecosystems.

Support forest regeneration. Reducing deer overpopulation allows forest understory plants to recover, which benefits soil biodiversity.

Protect soil structure. Prevent erosion and compaction by planting cover crops, mulching, and avoiding heavy machinery. Support farmers who use no-till, organic, and conservation farming practices.