The most diverse and most numerous life forms on land happen to live underneath our feet. As the great entomologist E.O. Wilson has written and spoken, "If I were to begin my life's work again, I would study the life in the soil around the base of one tree." This from a man who spent much of his career studying ants, probably the most familiar soil critter to us all and the smallest of creatures in most people’s minds.
Soil and its erosion were recognized as one of the first signs of land degradation by one of the founders of conservation, Aldo Leopold. In fact, it was his work in the Southwest and the serious erosion issues occurring there in the early 1900’s that began to influence his thoughts and was an essential component to developing his “Land Ethic” based on the lands “integrity”.
Photo: Mike Belknap
Soil is the upper layer of earth where the mineral world and the organic world become intertwined in a matrix of plant roots and fungal mycelium. In an average cubic meter of ground, there are 10,000,000,000,000 bacteria (that’s 10 trillion); 10,000,000,000 protozoa; 5,000,000 nematodes; 100,000 mites; 50,000 springtails; 10,000 rotifers and tardigrades; 5,000 insects, myriapods, spiders, and diplurans; 3,000 potworms and earthworms; 100 snails and slugs; and one vertebrate. All kingdoms of life are well represented in this hidden world.
Soil formation begins with the breakdown of rock. All rock, no matter how hard, will succumb to the relentless forces of wind, water, topography, climate, and time. These forces break rock into smaller and smaller sizes eventually creating sand, silt, and clay sized particles. These particles make up the mineral components of all soil types and, depending on the percentage of each of these particles, a soil’s texture is named. Equal contributions of sand, silt, and clay form a loamsoil, optimal for life. A sandy loam, which is characteristic of the Bull Run Mountains, has less nutrients, moisture, and humus than a loam soil.
Lichens are the first visible signs of life on the earth’s barren surfaces. These organisms begin a cascade of events that add to the connection between the mineral world and the organic world by combining and recycling both inorganic and organic components. Lichens, half algae and half fungus, have many advantages to begin life on rock, such as abundance and longevity (an individual lichen may live hundreds if not thousands of years). They can also produce acids unique to the kingdoms of life that aid the breakdown of rock. These pioneers pave the way for mosses, ferns, herbs, shrubs, and trees that take advantage of each other, as well as each bringing a myriad of life into the fold, including animal decomposers, detrivores, scavengers, herbivores, and predators. It seems that life has evolved to trap energy on land before its eventual loss to the sea. The more time nutrients from the soil cycle through living things the more time the natural processes that create new soil have to replace the eventual loss.
Bacteria and fungus do the bulk of the work to provide the minerals and elements that are the building blocks of all life. Solar radiation provides the energy that drives photosynthesis in autotrophic bacteria, lichens, and plants. Energy is stored in sugars that reciprocally feed the bacteria and fungus. The mammals, birds, reptiles, and amphibians, which are composed of the minerals from this matrix, add to the process by keeping the recycling process going. Many bring nutrients “back uphill” and away from the water as they decompose on land. This is a loop that is run over and over again, as players in the circuit evolve and go extinct, in a process that has produced the most fascinating results.
This all assumes the bedrock and mineral soil relationship is still intact¾a situation that many who are living in suburban and urban landscapes no longer experience in their daily lives. Many homes are built on and then surrounded by fill dirt brought in from other areas. In addition, our farming practices, especially since mechanization, have led to not only the loss of tremendous amounts of soil, but rely on inputs, such as nitrogen, produced in factories.
Photo: Mike Belknap
To keep soils constant or even building in nutrient capacity takes soil nutrients moving through a diverse food web. Humans have passed on knowledge through language and writing for thousands of years and many have “discovered” the importance of maintaining natural communities that starts with intact soils. However, as Aldo Leopold famously wrote, we continue to “…live on the land, but not by the land.” Maybe it is time to heed those words.