In Northern Illinois, there is an abundance of beautiful native plants: purple coneflower, butterfly weed, black-eyed Susan, switch grass, maple trees and oak trees, just to name a few. The word “biodiversity” implies not just a multitude of plants, but includes all types of living things, like birds, mammals, amphibians, and insects. Because we can see all these things above ground enjoying the sun, air, and rain, it is hard to imagine that the underground world could be as rich and diverse.

However, within the soil there are hundreds of burrowing earthworms, thousands of miles of fungi, millions of insects and billions of bacteria, and other microorganisms busy at work under our feet. Soil-dwelling organisms make up a great deal of biological diversity across the planet, yet these invisible creatures are often overlooked. Many of us often forget the wild world underground. The number of species in the soil and their important ecological functions are so rich that ecologists have called soil the “poor man’s tropical rainforest.”

Digging Deeper

When most of us hear the term biodiversity, we think of trees and flowers, of birds chirping over our heads, critters scurrying at our feet, frogs calling in the distance, and insects buzzing around our faces.  People tend not to realize that there are many types of organisms in the soil.

Soil organisms are important for decomposition, gas exchange, and making nutrients available for plants.  In the soil itself they make their homes, they reproduce, and they hunt and eat one another, just like creatures in above-ground communities. Changes in these animals can reveal habitat pollution long before other signs are visible, as recent research has shown. The underground community is so vast that only a fraction of the creatures living there have been studied.  As the famous ecologist, E.O. Wilson has said, we there is much we do not understand about these “little creatures that run the world”.

Amazingly, only a small proportion of soil-dwelling species have been described and the scientific community does not yet understand much about their community structure, dynamics and function.  Why?  Perhaps it’s because humans aren’t drawn to these creatures, so it takes a rare scientist to study them.  Furthermore, it’s much easier to ignore the teaspoon of soil that makes possible the purple coneflower’s (Echniacea purpurea) beautiful bloom or the tiny fungus (penicillin) that cures infections.

What do we know?  We know that there are thousands of creatures beneath our feet.  The majority of all terrestrial insects live in the soil for at least some part of their lives.  We know that they are very important for natural areas, agriculture, horticulture, and sustaining all of life on earth. 

Even many animals, such as crayfish, voles, frogs, toads and snakes make the soil their home during our frigid winter months. In his book, The Diversity of Life (1992), E.O. Wilson estimates that somewhere between 5-10 million species different species live below the soil, most of which are insects.

This wealth of diversity below ground is one of the reasons soil has been referred to as the “poor man’s tropical rainforest” (Usher et al., 1979). The similarities between the rainforest and the soil go beyond the sheer number of species present. Both the soil and the rainforest maintain a fairly constant temperature, making the environment hospitable year-round for its native species. habitats also provide vital functions of decomposition, nutrient turnover, and air purification, as well as supporting the plants and animals on which we depend. These benefits are called ecosystem services” (Nature’s Services, Gretchen Daily, 1997) because they provide important benefits to human societies.

Next time you are talking a walk, admiring the wealth of plants and animals around you, don’t forget to peer at the soil beneath your feet and imagine the whirlwind of activity that makes all life above ground possible.

By the Numbers:

–       The soil below one square yard of woodland could contain over 200 species of arthropods (such as insects, crayfish, and spiders) and up to 1000 species of soil animals in total.

–       There are up to 7,700lbs of bacteria in one acre of soil.

Written by Lauren Umek, Environmental Science Program, DePaul University

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