By Dana Visalli

From The Methow Naturalist Fall 2017
Summary by Ed Schein

The most productive ecosystems, in terms of biodiversity, are the soils under our feet. One teaspoon of healthy temperate forest soil contains from one million to one billion bacteria, miles of fungal threads (mycelia), several hundred thousand amoebae, several hundred nematode worms, and an assortment of micro-arthropods. It has been said that all terrestrial life lives only six inches from desolation and death, because all terrestrial life is dependent upon the teeming biological activity of the top six inches of soil to support the plant and animal life above ground. (Opening paragraph by Dana Visalli)


This article explains the origin of soil on our planet as gleaned from a booklet “Soil Biology Primer,” available online. You must read the article to begin to understand the evolution of our most important resource. A few facts to get you interested:

None of the multitude of soil organisms are photosynthesizers, so they could not exist in the soil until organic matter from dead plants became available as a food source.

All living things require nitrogen, but only certain bacteria are capable of pulling it out of the atmosphere where it exists as a tightly bonded molecule, N2, and alter it into a form usable by life.

Nitrogen-fixing bacteria live on the roots of plants, and trade nitrogen for a supply of the plant’s high-energy sugar.

Dead plants are rich in hydrocarbons—they still retain the high-energy electrons put in place by photosynthesis. They are also absorbent, retaining moisture when it falls from the sky.

Dead plants contain the building blocks of life: carbon, nitrogen, phosphorus, and potassium.

There can be as much as 100 times more carbon dioxide in the soil as there is in the atmosphere.

Some carbon dioxide combines with water to form carbonic acid, which increases the rate of erosion of the rocky substrate ten times more than mechanical weathering, increasing nutrient supply to plant roots.

The most biologically productive areas of the oceans are near-shore, where there is a constant flow of organic matter along with nitrogen, phosphorus, and potassium, all made available by the abundant life in the soil ecosystem.

Some ecosystems have no photosynthetic capacity of their own, like soil OR the fast-flowing, cold waters of Bear Creek. Streams do attain a photosynthetic algal coating on the cobble substrate, but that’s only a small fraction of food energy needed to run the stream ecosystem. The rest comes from organic matter—for example, LEAVES: 20-30 tons of easily broken down plant material falling to the ground per acre per year! All that is needed is an army of shredders and scrapers—the invertebrates in the soil and in streams—to break down the organic material and make it available to fungi and bacteria, which do the final deconstruction of organic matter.

What happens in winter when photosynthesis ceases? Conifers help as solar collectors with their rounded needle shapes when days are above freezing. But spawning salmon provide the winter link by utilizing oxygen, with its increased availability in cold water and in the winter. Salmon eggs buried in gravel only obtain oxygen from water percolating through the substrate. They emerge from the gravel just in time to greet the increasing sunlight and photosynthetic activity of spring.

The next time you experience the greening restoration of the Bear Creek watershed, remember ALL LIFE DEPENDS UPON SOIL!