Redefining Soil Fertility

Spring 2007
There is No Soil Fertility Without a Healthy Forest

Branches under 3 inches in diameter, from deciduous trees, can be chipped to make a soil-building, crop-fertilizing amendment.  English photo.

by Céline Caron

Terms in italics are defined in the glossary at the end of this article.

Have you ever wondered how a forest can grow and reproduce with no addition of fertilizers or irrigation; without tree transplants; and how insects are controlled without pesticides? Natural forests thrive and regenerate without human intervention, fertilizers or biocides. The only sources of energy are the sun and water. The forest is a living machine working with living material, and from this living machine comes soil fertility.

When we see the soil as a biological entity, we reverse the actual definition of soil fertility completely. Forest ecology must inspire and guide farmers around the world.


Pedogenesis is a new word for a natural, basic process of soil formation and maintenance. Most living beings responsible for pedogenesis perform underground and are invisible to the human eye, so “soils are the most poorly researched habitats on earth. The functioning of this thin dark covering on the surface of the earth is vital for the survival of the biosphere in its present form.” (“Life in the Soil. Soil biodiversity; its importance to ecosystem processes.” Report of a Workshop held at the Natural Museum, London, England, August 30-Sept. l994. Diana W. Freckman, Ed., Natural Resource Ecology Laboratory, College of Natural Resources, Colorado State Univ., Fort Collins, CO 80523-1499)

Pedogenesis has occurred over hundreds of millions of years. Drastic changes in climate 60 million years ago gave birth to hardwood forests and their soils, which are a major asset for nutrient and energy conservation. These soils became a “bank” holding the highest biodiversity on earth. Pedogenesis develops interdependent worlds of multiple species inside this one world, the soil.

Our understanding of pedogenesis has increased since residual tree branches (Ramial Chipped Wood, or RCW) were studied in Quebec in the 1970s. At first, we did not know there were major differences in the behavior of forests. ‘Wood chips’ was a general term for any residue from both coniferous and deciduous forests, either stem wood or branches. Then we discovered a difference between stem wood (over 3 inches in diameter) and branches (under 3 inches in diameter) and their differences in nutrients. Furthermore, trials revealed a very different effect on the soil: Branches from deciduous trees produce stable humus. This stable humus is the basis of the living soil.


Ramial wood, stems and branches under 3 inches in diameter, is the most nutrient-dense part of trees and represents one-third of the biomass produced by the wood industry – two billion tons annually worldwide. Ramial wood captures the energy of the sun and stores it in its living tissue. Added to soil, RCW improves and maintains the structure, fertility and stability of agricultural soil for a long time, reconstituting natural forest soil on agricultural land. The great availability of RCW and its enhancement of trophic (food) chains have garnered interest in this once-rejected but precious material.

RCW is rapidly invaded by white fungi (Basidiomycetes), which instigate complex trophic chains that structure the soil, manage nutrients, limit diseases and pests, and control water and fertility.

In the forest, branches fall on the soil, disintegrate naturally (faster if they are fragmented) and initiate a complex food chain, developing stability and resilience in the soil. These trophic chains regulate the availability of organic and mineral nutrients.

The Living Forest

Originally, about 60% of Earth’s land surface was forested. In some places, the forest has evolved from coniferous to deciduous, which are beautiful, efficient and sustainable. They contain a great number of species in the hypogeous (above ground) and epigeous (underground) ecosystems and a high degree of resistance to long periods of disturbance.

Forests regenerate themselves with their leaves, twigs, roots and the help of a multitude of fungal mycelia, small insects, worms and rodents. The invisible work by underground organisms creates long-lived humus. The scientific genius of forestry and pedogenesis helps us appreciate the biology, ecology and integrity of the primeval forest.

Biodiversity enhances these dynamics. Plantations of deciduous trees will never offer the biodiversity of natural forests. Of the world’s 1.4 billion hectares of remaining primary forest (a natural forest with no sign of human impact), 6 million hectares are lost or degraded each year – a loss of forest area and of biodiversity and SOIL.

The Living Soil

Soil fertility comes, with the help of fungi, mainly from the lignin of deciduous tree branches, as well as polyphenols, sugars and proteins in the branches, and the microorganisms that they support. Lignin, a fibrous macromolecule, is crucial in conducting water through trees and is removed in papermaking. (So, note that engineering tree species without lignin to suit human wants would destroy the soil.)

Forest soil is sustainable while agricultural soil has to be fertilized constantly. The soils in deciduous and tropical forests have very long cycles, often centuries, with a great diversity in species. Coniferous forests, found in cold and temperate climates, are not suitable for agriculture because the asymmetrical lignin (guaiacyl) of conifers, once in the soil, produces polyphenolic inhibitors that block soil formation. This type of lignin is also found in many tropical tree species, but high soil temperatures there break the inhibitor effect somewhat.

Almost all the dynamic of life is managed through the soil. The physical condition of the organisms in the soil is a matter of life and death to organisms living on top of it – including humans. Southern Quebec and Ontario, and parts of New England, have deciduous forests and their fertile soil. Unlike coniferous forests (whose trees die simultaneously), the diversity of species and soil fertility are much greater in deciduous forests, so these forests can regenerate themselves perpetually in all their biological dimensions, species by species, year after year, century after century.

Living soil, RCW and fungi smell good. Dead or rotten materials smell bad and asphyxiate the soil until microorganisms turn the decaying process around and life starts again. There is a tremendous difference between pastured animal manure and confined animal slurry: The latter comes mostly from a corn diet and is diluted with water, so has little fiber; but both are degraded materials that are not part of the upgrading process of pedogenesis.

The power of the soil is revealed by the complexity and diversity of the living beings on this planet, and RCW helps build this diverse life. Rich stands of red oak, sugar maple, beech, yellow birch, linden and ash give the most diversity and much better results than lower-quality stands, such as red maple or trembling aspen. A mixture of species gives positive short- and long-term effects.

Soil degradation can be overcome permanently with RCW. Research published during the last 20 years shows that the deciduous forest is the only model of sustainable production, not only due to the complexity of its canopy but also because it regenerates itself and the soil on which it grows, independently of climate, geomorphology and the minerals on which it rests. Amazonian ecology is the most striking and convincing example.

When forests disappear, so does soil fertility; then water; and then deserts are created. When a forest is cut, a major change occurs in the soil. Knowing that the soil is a living organism and that water is indispensable for agriculture, we should be very worried about the disappearance of forests and the necessity of irrigation. All is intrinsically interrelated.

The Evolution of Agriculture

Deciduous forests created fertile soil on which agriculture was started 10,000 years ago. The slash-and-burn method of cultivating soil at the beginning of modern humanity was successful because it left periods of about 20 years before another field was cleared – enough time for the forest to reclaim the degraded soil. Mankind evolved when food could be grown on these fertile soils, derived from hardwood forests and regenerated naturally between periods of cultivation.

When humans started to settle, they first fertilized fields with manure from pastured animals, which gives short-lived fertility. Compost and green manures used by organic growers also give short-lived humus and aim to recover certain nutrients for short-term results without restoring truly long-term soil fertility. Thus, soils must be amended with compost annually or at least biennially, and even then their lack of lignin is noticeable. Soils amended with RCW, however, can go for three to five years without another application, and residual effects last much longer.

Organic and biodynamic agriculture are better than modern chemical agriculture, which uses synthetic and dead materials, but none of these consider the forest as the basis of fertility.

In the mid-1900s, scientists began recommending synthetic mineral nutrients in earnest – especially nitrogen, which has a major impact on yield. Soon nitrogen was overused for such major crops as maize – destroying soil structure and soil fertility. Excess nitrogen caused excess activity of soil microorganisms, which consumed the energy contained in complex organic molecules that were rich in carbon and nitrogen. Carbon was released to the atmosphere and soils were degraded.

How did we come to see soil as a lifeless support for plants? Dirt, garbage, detritus, animal carcasses, decomposition, rot, excrements, paper mill residues, sludges, slurries, manures, compost (which is the result of degradation), etc., belong to the realm of the dead. How could we reduce the soil to NPK (nitrogen, phosphorous and potassium) only, when so much life populates the soil? Aren’t fungi, collembola, arthropods, nematodes, acarians, arachnids, of which tens and even hundreds of species exist in forest soil, living beings?

Agronomic techniques often reduce soil to its mineral function. Organic and biodynamic techniques maintain fertility but do not build it much. No-till techniques and worms in organic and biodynamic agriculture help. Composting frees mineral elements but does not initiate a complex food chain capable of regulating and regenerating itself. Only pedogenesis offers this possibility.

There is an enormous difference between farms started on grassland and farms started on forest land. Forest soils are dominated by fungi, while short-term, humus-fertilized soils are dominated by bacteria. Fungal mycelium continues to develop in the winter, whereas bacteria become encysted. Fungi, more than other living organisms, can extract tightly bound water and raise the water table, which is excellent in dry areas. Fungi, not bacteria, must be at the heart of the living soil system.

The same difference exists between farms operated with compost, horse, sheep, goat and/or green manures and farms improved with twigs that contain lignin and polyphenols. Peasants who live close to nature have this inner knowledge, and science can now explain part of their instinctive practice. Their preference for using goat rather than sheep manure, for example, is probably because goats eat shrubs, which contain lignin, and sheep eat grass, which has no lignin.

Uncultivated agricultural soil returns to forest, but forests never naturally become agricultural soil. Agriculture starts with good forest management.

Research by the Laval University group ( brings a new vision and useful knowledge regarding soil. Many conclusive experiments were carried out on potatoes, strawberries, small fruits and orchards in Quebec; on tomatoes and eggplants in Senegal, the Dominican Republic and Ivory Coast; and on maize and rye in the Ukraine.

English photo.

Investing in Soil Fertility

The natural life cycle of agricultural fields must be maintained through additions to the humic bowl after residues from the previous crop have been depleted, in order to build new organic, biological and mineral nutrition for the next crop. This action cannot be replaced with overdoses of chemical fertilizers, which harm soil life.

We can cultivate agricultural soil so that it keeps its fungal-dominated, forest origin by adding RCW. Gathering and shredding branches is strenuous and labor-intensive but rewarding work. For good chipping the branches must be cut at an angle of 57 degrees and, if you use a shredder, the blade should rotate at 12000 rpm for one knife, 6000 rpm for two knives, and so on. It is better to shred branches lengthwise than cut them perpendicularly to expose as much inside as possible. As small equipment takes more energy to use than large, and moderate sized equipment yields only 1 cubic yard per day, it is best to rent a good shredder once a year or arrange to have tree trimmers dump their load on your farm.

We must raise our food from forest-based systems and include biodiversity on our farms by reintroducing climacic trees and augmenting the few remaining stands. Long-cultivated soil must be bio-stimulated and rid of nitrates. To do this, fresh RCW is spread in a thin layer (1 inch is optimal; 1-5/8 inches is the maximum; or 80 to 100 cubic yards per acre; or about 2 cubic yards per 1,000 square feet) after harvest in the fall (or on frozen soil, to prevent compacting it). We copy nature, which drops twigs and leaves. In the spring, RCW is incorporated in the top few inches of soil; then, ideally, a legume is sown and the soil is not cultivated for the next two years.

Mulching with RCW is also excellent for gardens, perennials, orchards, tree plantations, forest floors and hedges. At a thickness of not more than 4 inches, RCW protect plants from frost heaving and helps soils retain water.

RCW can be used as litter in barns; current recommendations suggest composting and managing it like manure afterward.

One cubic yard of RCW has the same effect as 90 pounds of straw or sawdust. On a cattle farm, RCW can be used on the paths where animals walk to pasture fields, where it will restructure the soil and retain nitrates. After a few years, the layer can be raked and spread on fields, and fresh RCW can be put on paths.

RCW controls erosion rapidly. It stimulates the life of the soil (worms and fungi), then raises the fertility 5 to 10 times faster than manure. RCW also transforms nitrates into organic nitrogen, held in the top 6 inches of soil, where plants need it most. Very low levels of water-soluble nitrate will then leach into waterways. This practice can be very useful in intensive cattle raising areas where water quality control is necessary and manure use is severely restricted—although reducing the demand for factory-farmed meat is also part of one solution to this issue. At the maximum dose now permitted in order to minimize nitrate leaching, manure would take 100 years to raise fertility by 1%. Ramial wood, from which very little nitrate leaches, can do it l0 times faster.

The RCW-legume association should interest organic farmers especially. In Belgium, trials with alfalfa showed that weeds could be controlled effectively while multiplying RCW efficiency five-fold (by adding nitrogen to the soil). The RCW-alfalfa association, used locally, also reduces fertilizer importation costs.

My 28-Year Observations

Don’t panic if mushrooms invade your soil after you spread RCW; they indicate biological activity. Fungi are “the masters of pedogenesis,” says Prof. Gilles Lemieux. One of the first fungi you will notice in RCW are basidiomycetes; their mycelium will spread wherever RCW has been applied. Rejoice: Your soil is working!

Actinomycetes will also appear. For three consecutive years, we delighted ourselves with Stropharia rugoso-annulata, an edible mushroom cultivated commercially in Hungary, which grew profusely in our raspberry and strawberry patches. Unfortunately I cannot say which tree species is involved, but the RCW contained maple, cherry and alder.

Where RCW is applied in great quantity, the soil will be elevated a few centimetres, especially on wet mornings. This indicates that soil fauna are present. Hundreds or thousands of worms will cover the soil at night. After many years of application, salamanders will proliferate. We have observed two kinds of baby salamanders in one garden, confirming that the water table has been raised and sufficient moisture is available for these animals. (RCW raises the water table up to 50%). Old-growth forests may support one to two salamanders per square yard, while salamanders are absent long after timbering, clearcuts and biocide use in forests or fields.

The color of the soil is much darker after RCW additions. The soil has a soft, humus-like feel and scent. Sandy soil seems to respond to RCW additions faster than clay soil. The only noticeable harmful effect observed so far is lower potato yield immediately after applying poplar RCW. To prevent this, seed a legume and a cereal during the year of RCW application and the year after, then plant potatoes the third year.

Yields increase dramatically with RCW applications, relative to all other types of agriculture. Tomatoes, peppers, beets, corn, strawberries and raspberries produce exuberantly. Our gardens now produce more on less than half their original size. Root vegetables (carrots, beets, onions, etc.) are much sweeter after years of RCW application.

We rarely water our gardens, because RCW helps retain soil water. Plants are healthy, with occasional comfrey tea sprays on solanaceous crops, which use a lot of potassium; and wood ash water sprayed on turnips and carrots twice in August to control worms.


The soil is the kingdom of life. Deciduous forests can regenerate soil richness after human anthropocentrism (bioadversity, a term coined by Quebec cardiologist Yves Tessier) has destroyed it. Forests, plants and animals share many of the same sugars, proteins, lipids and physiological mechanisms. If we humans want to survive, we must take care of the soil. The primary goal of every farmer must be to produce and maintain stable humus in the soil.

The soil today is yesterday’s forest being transformed into tomorrow. Humans must integrate the science of forest pedogenesis into their methods of cultivating soils and growing food.

Professor Gilles Lemieux of Laval University in Quebec is the brain behind pedogenesis. This article was written with the help of more than 200 research documents he published and my own observations with the use of RCW on our forest trees, orchards and gardens since 1978.

Céline Caron is an ecologist and Earth doctor. She is a long-time practitioner of organic agriculture in Quebec, a friend of rivers, wetlands, forest and soil, and simple living. She writes in both French and English.


Aggradation: A dynamic upgrading process; the opposite of degradation.

Aggregates: Groups of particles held together by a “cement” or “glue” of biological origin and acting as structural elements for the soil. Soil aggregates provide refuge and food for microfauna.

Biotransformation: the transformation of twigs, roots and leaves into humus by fungi and microorganisms.

Climacic: relating to all phenomena deriving from the climax (such as a climax forest), or the most stable ecological structure that can renew itself under local constraints of climate and geomorphology.

Coniferous: trees that retain green leaves throughout the year.

Deciduous: trees that drop all of their leaves every fall.

Desertification: creation, by humans and nature, of biological entities that are restricted by certain limiting factors, of which water is the most important

Ecosystem: a biological system allowing beings of different levels to live in harmony according to more or less closed cycles

Epigeous: above; applies to autotrophous plant ecosystems such as the forest

Humic bowl: encompasses digestive and fecal systems of soil organisms and fauna, including branches and rootlets.

Hypogeous: under; particularly ecosystems inside the soil

Lignin: A macromolecule that makes up about one-quarter to one-third of the dry mass of wood

Pedology: the science of soils

Polyphenols: compounds derived from phenol and formed of benzene rings and hydroxyl groups.

Pedogenesis: The whole, natural process (including effects of organisms) of creating and maintaining soils within a dynamic that includes rodents, fungi, lignin, polyphenols, sugars, etc. Pedogenesis creates soils that can supply the nutrients necessary for plant growth and that can maintain hypogeous and epigeous biological balances.

Pedosphere: the outermost layer of earth, including soil and material subject to soil forming processes; this includes the humus of fertile soil that unifies the organic and the mineral worlds; the biggest reservoir of biodiversity and the only true source of sustainability on the planet

Ramial wood: twigs with a diameter of less than 3 inches

Stable or long-lived humus: humus formed with the lignin of deciduous trees, as opposed to short-term humus derived from animal and green manures and compost

Short-term humus: compost, animal and green manure

Stem wood: trunk wood, with a diameter over 3 inches

Trophic chains: communities of plants and animals that transform plant tissues and transfer the nutrients and energy of the soil toward plants


Caron, Celine, G. Lemieux, Lionel Lachance, “Building Soils with Ramial Chipped Wood,” The Maine Organic Farmer & Gardener, Dec. 1998/Feb. 1999

Caron, Celine, “Pedogenesis: The Importance of Deciduous Trees in Forest Ecosystems,” The Maine Organic Farmer & Gardener, Dec. 1999/Feb. 2000.

Caron, Celine, “Oak Trees from Seed to Seed,” The Maine Organic Farmer & Gardener, March/May 2000

Caron, Celine, “What is a Forest,” The Maine Organic Farmer & Gardener, Sept./Nov. 2000

Caron, Celine, “Connecting with the Terrestrial Ecosphere,” The Maine Organic Farmer & Gardener, March/May 2006

Ramial Chipped Wood: A Summary

Chip, as soon as possible after they are cut, branches of hardwood trees (oak is the best but a mixture of red oak, sugar maple, beech, yellow birch, linden and ash is very good) after leaves have dropped.

Apply a 1-inch-thick layer to soil in the fall. This equals about 80 cubic yards per acre, or 2 cubic yards per 1,000 square feet.

Mix the RCW with the top 2 inches of soil.

Ideally, sow a cover crop associated with a legume the following spring and a food crop two years after that.

Do not plow the soil for three years after applying RCW, if possible.

The major effect of this application should last at least three years, with smaller effects lasting 10 to 15 years. Four years after the initial application, and annually after that, add about 8 cubic yards per acre, or about 5 cubic feet per 1,000 square feet of soil.

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