Some Uses of Woody Biomass in Gardening and Regenerative Agriculture
By Michael Pilarski, Friends of the Trees Society, and Global Earth Repair Foundation. Febuary 6, 2020.
[This paper originated as an outline for January 28, 2020 presentation by Michael Pilarski in Port Hadlock WA. We were honored to have the participation of Paul Gautschi, world-famous pioneer of gardening with wood chips. Further on in the article is the url link to his movie Back to the Eden.]
There are numerous pathways that woody biomass can be incorporated into the soil fertility cycle on farms and gardens. Here we will examine some ways to utilize the various sizes of material and some ways to obtain multiple functions and yields from tree trunks, stumps, branches/limbs, twigs, bark, leaves, chips, hogfuel, sawdust, biochar, ramial chipped wood (RCW), forest litter, duff, cardboard, and paper. Yard-scale, farm-scale and forestry.
This is a huge topic which I have been enamored of for many years. Woody biomass in farming and gardening is, or could be, a valuable strategy pretty much everywhere in the inhabited world. It offers one of the best ways to sequester carbon in the world. Grasses and non-woody vegetation offer a smaller but important role. Grass/livestock systems may be able to sequester carbon faster then woody plants in semi-arid regions.
Currently a huge amount of woody biomass is burnt every year on the planet. I am not going to tackle the issue of forest fires in this article, nor firewood but rather the deliberate burning of woody materials to get rid of it. Specifically burning of yard waste and slash burning in forestry operations. How to divert woody biomass to more productive ends. Highest and best uses.
This article explores how we can use woody materials in ways which slow down the return of their carbon to the atmosphere and which increase food production and ecosystem health.
Woody biomass is like money in the bank. It pays out over 5 to 25 years and even longer depending on the decay time. It is a relatively slow release fertilizer. A chip mulch is usually digested in 3 years. This depends to an extent on the level of soil microbial activity the soil starts out with. This digestion accelerates starts in the first year, accelerates in the 2nd and is in the nature of a bacterial orgy in the 3rd year after the fungi has pre-digested the chips and softened them up for the bacteria and myriad other soil life in the latter stages of digestion. By the end of the 3rd year the parent material is largely indistinguishable. There will still be follow-on effects as the more recalcitrant carbon is gradually chewed up. Once established, the big build-up in soil life can continue on an upward curve if kept fed and not disturbed over-much.
You could think of the soil (including the soil surface) as like one big stomach. Just like our stomach, the soil is full of microbes. All organic matter is food to the soil stomach and they are going to digest it. Leaves last one year, ramial chipped wood lasts 2 years, wood chips last 3 years. It takes longer to digest logs and stumps. Up to 25 years and in some cases even longer. Logs and stumps digest a lot quicker if buried in a hugelkultur rather than lying on the surface. Suspended in the air is the slowest.
Burning woody biomass to get rid of it is like burning money. It is noble for land-owners to give unwanted woody biomass to people for hugelkultur projects or to municipal wood chipping at transfer stations which are then given away, sold, or composted.
The Earth is a huge breathing organism. It’s outbreaths and in-breaths are of many kinds. One of the largest is the yearly in-breath and outbreath of carbon dioxide. The most notable aspect of this cycle is the in-breath during the northern hemisphere’s growing season and the outbreath during the northern hemisphere winter. Huge quantities of co2 are taken up by the plants during the growing season: crops, grasses, trees and vegetation grow and fix carbon. During the winter much vegetation dies, falls to the ground and decomposes. Most of this carbon is returned to the atmosphere. Of course this yearly cycle also happens in the southern hemisphere but due to its much small landmass, the northern flux is many times larger.
The general public tends to think of co2 levels in the atmosphere as relatively stable, just going up a little each year due to humanity’s fossil fuel burning and other nefarious deeds. Few are aware of this immense annual flux. So when it comes to CO2 drawdown and reducing carbon in the atmosphere one of the biggest drawdown strategies is to plant more trees, increase vegetation and build carbon in soils. These are the best strategies we have and need to be pursued full speed ahead, which is one of the goals of the Global Earth Repair Foundation. This article discusses how we can reduce the winter flux of carbon back into the atmosphere by reducing the burning of wood waste as well as how to influence the decomposition processes to yield more stable carbon compounds in the soil. This article will focus on woody biomass. There is much to say about judicious management of non-woody vegetation as well, but more on that in another article.
Woody biomass comes in three forms:
1) Fresh
2) Dried
3) Pre-digested. Composted or mushroom substrate or natural decay.
A healthy ecosystem will have lots of live carbon, lots of decaying carbon and lots of carbon as a form of stable humus and/or biochar. In tropical forests, decay rates are fast and dead material decays rapidly and it is hard to achieve humus buildup. Most of the carbon is held in the live biomass. Biochar is a great addition to long-term carbon sequestration in these soils. The Terra Preta soils of the Amazon are a great example.
How much woody biomass of various types can be extracted from forests without damaging the forest’s productivity? This will depend on the forest. Jean Pain said he could sustainably harvest 40 tons of wood chips every 8 years from 1 hectare of forest in the French Provence. This is 2 tons per acre per year. This figure would be much higher in the Maritime Pacific Northwest.
In the long run, the goal is that most plots of land will produce their own biomass needed for ecosystem function, biodiversity and productivity. We can view this whole strategy of using imported woody biomass in agriculture as a stopgap measure. Or perhaps a better word would be a “kickstarter” measure. We need to rapidly increase carbon capture in the worlds soils and maximize soil health. Some judicious use of woody plant biomass can help accomplish this quicker. The end goal of most systems is to create a self-mulching system where the system generates enough woody biomass for its own health and importing woody materials from offsite is not needed. There are ways to bootstrap a soil up without importing woody biomass, but bringing in outside biomass can greatly speed things up. The bootstrap method involves planting adapted tree, shrub and vine species that will grow well under the site’s current conditions and over time they will create the conditions for additional species and create woody material that can be used on site. This can be done with native plants and/or non-native plants on a spectrum from totally native to totally non-native and everything in between. Depends of the many other parameters of the site objectives.
Several end goals, huge carbon sequestration; rebuild the health of the world’s soils and ecosystems; produce more food and natural resources to enable local food sovereignty and vibrant local economies. This can contribute to climate stabilization. To do this on a piece of land involves maximizing photosynthesis. How much sunlight can be turned into sugars, carbohydrates, organic matter? This usually calls for a multi-layer system of high-canopy, mid-canopy and understory plants with trees, shrubs and herbaceous plants. The woody plants accumulate carbon in living tissue including roots, in decaying plant matter and in the soil. Particularly important is the building up of long-term stable soil carbon such as humus, humates and biochar.
Tree trunks, logs, whole
Some uses: Hugelculturs, bed edging, terracing,. In the wild they can be placed cross-slope to help control erosion. Can be used for mushroom culture such as Shitake. Snags in the garden.
Stumps, whole.
Some uses: Hugelculturs, “Replanted” in gardens. Stumps have many uses in ecosystem restoration and are in used in river, stream and wetland restoration. Stump piles also create habitat in forests (preferable to burning them in slash piles). I make stumps of a sort in my gardens by partially burying rounds of wood. They perform valuable ecosystem functions and make good seating and working surfaces. Stumps can be used in place for small hugelkulturs. This is for dead stumps, not for fresh stumps of trees which are going to vigorously resprout.
Branches/limbs,
Some uses: Hugekulurs, large mulch, cut to lay flat on the ground. Where generated in the garden or farm utilize as close by as possible to minimize transport energy. Fresh as ramial chipped wood.
Twigs.
Some uses: Mulching. Can be used whole, chipped or shredded. Livestock bedding. In composts. Fresh as ramial chipped wood.
Bark.
Some uses: Mulching. Can be used whole or chipped. Bark is rich in minerals compared to wood and has a better carbon to nitrogen level. Fresh as ramial chipped wood.
Leaves.
Some uses: Great for feeding worms, composts, mulch (mitigate against blowing away). Livestock bedding. Tree and shrub leaves can feed a wide variety of livestock. Match the plant species to the animal species. The output is manure and livestock products.
Chips.
Some uses: Mainly used for garden mulch, landscaping and intensive farming. Livestock bedding. Can be used as a substrate for mushroom cultivation.
Back to the Eden is a documentary movie about Paul Gautschi, world-famous pioneer of gardening with chips at his location on the north side of the Olympic Peninsula. 40 years of experience as of 2020.
https://www.backtoedenfilm.com/
Hogfuel.
Hogfuel is half wood chips and half bark. It is produced for industrial power generation, usually at, or near, lumber mills. They do this to get some uses out of bark as a waste product. Bark alone is too dense for them to burn but if they mix it with 50% wood it burns fine.
Some uses: Mainly used for surface mulch. Livestock bedding. The high bark content makes it a better fertilizer than wood chips alone. I have used it extensively on my micro-farm here on the Olympic Peninsula because 50-yard semi-loads currently cost just under $400 delivered. I have used six semi-loads (300 yards) so far on one acre of land over 4 years. This is a big input (all spread by wheelbarrow) but the results are worth it. The amount needed per year goes down over time as the soil quality and yields goes up. One acre of soil can digest a lot of woody biomass! Here is a video of me planting into a sheet mulch. https://www.youtube.com/watch?v=01yDYbGpVgo
Ramial Chipped Wood (RCW)
This is a technique developed in Quebec in the 1980s on. Small-diameter, green, woody material is ground up and applied to the soil surface as a fertilizer in crops. It is found to be a very good fertilizer for almost all kinds of crops. Ramial Chipped Wood: the Clue to a Sustainable Fertile Soil, by G. Lemieux and D. Germain. https://www.researchgate.net/publication/228364133
Shredded wood.
Frenchman Jean Pain developed one of the first wood shredders and utilized the shredded wood in massive compost piles from which he generated hot water for up to 18 months. He also encased digester tanks inside the pile to produce natural gas. At the end he was left with a high-quality compost which he used in gardening and sold to farmers. The wood came from a scrub forest that he was cutting firebreaks in. A form of forest restoration. See Youtubes
Jean Pain – English – Part 1
7:30. 150,129 views. Jul 15, 2008.
Jean Pain – English – Part 2
7:43. 65,666 views. Jul 15, 2008
Sawdust.
Mulch, Trickier to use as mulch then chips as it can form mats. Animal bedding. Some sawdusts are toxic to humans. Sawdust of such species needs to be handled with care.
Wood Shavings.
Mulch. Animal bedding.
Forest litter.
This can be raked up from small patches in the forest and used in the garden, in composts and as mulch. It also is a form of inoculum as it will bring in a new complement of shredders, arthropods, decomposers, fungi, etc. When I have used this as a mulch, I also brought in seeds of native woodland plants which germinated and added to plant biodiversity in the garden.
Duff.
This can be taken from the forest in small amounts and used in the garden as a form of inoculum, (as above) but yielding an additional series of organisms. Rake aside litter, scoop us some duff and replace the litter. Natural Korean Farming and JADAM both go into detail on how to do this.
Biochar.
Biochar is very long-term carbon sequestration with lots of benefits to the soil. There are many uses for biochar in agriculture/gardening. It fulfills many functions in the soil. Habitat for soil organisms. Soil “battery” of nutrients (nutrient capture and release), water absorption. Improves heavy soils and light soils. Added to compost for additional nutrient capture and moisture levels. Added to animal bedding and livestock facilities to reduce odor and capture gases. There are small cooking stoves that use small-diameter wood and produce biochar as a side product (instead of burning the wood completely to ash). These stoves produce far less emissions and would improve the health of hundreds of millions of people worldwide, particularly women who suffer lung and eye ailments from smoke from cooking fires. Great source of info on these stoves are at http://www.ethoscon.com/
Charcoal is a common component of many soils worldwide. Forests, grasslands, shrub steppes and other systems which experience fire. One of the reasons the US Midwest prairie soils are so black is the presence of large quantities of micro-charcoal from millennia of prairie fires. Most (all?) indigenous people increased fire periodicity in their landscapes. Usually with well thought out, low intensity cool burns, instead of catastrophic wildfires. Adding biochar to soils is nothing new. Mother Nature and humans have been doing it for eons.
F.H. King in his classic book on the traditional farming practices of China and Korea, Farmers of Forty Centuries, describes how Chinese farmers spread powdered charcoal on the snow at the end of winter to melt the snow quicker to get ground for earlier planting. Once the snow was melted they applied another even layer over the surface of their rice nursery beds to increase soil temperature.
Cardboard
Permaculture started popularizing sheet mulching with cardboard 40 years ago and it is used extensively these days under various names. Cardboard in sheet mulches usually decomposes in 3 to 9 months. There has been testing that a healthy soil biology gobbles up the toxins in cardboard. Preferably use the basic kraft cardboard. I avoid colors, inks and Chinese cardboard.
Paper
Can be used in sheet mulching. Worm farmers often use shredded newspapers in worm bins.
Boards.
Can be used for mulch aand garden pathways. Great habitat underneath. Can be used as slug traps for hand picking or have some ducks standing by when you turn the boards over.
Livestock bedding.
Chips and sawdust are widely used for bedding. The carbon helps sequester the nitrogen. A sprinkling of biochar helps.
Hugelkulturs use logs, and other woody material to create garden beds. Farm-scale ones can be made, but it is mostly for intensive production. In most climates they are raised beds, but in arid regions they can be made in trenches. Depending on the diameter of the material and its decay rate the woody material can take decades to completely decompose. All the while they are a source of fertility. Some of the material becomes long-term humus. If the soil used in/on a hugelkulter doesn’t have much clay, add some clay to assist in humus formation and water retention.
See 5 of my hugelkultur videos at https://www.youtube.com/channel/UCylekw2DaAsQHsIWaR-js_A
The energy cost of chipping and transport of woody material.
Chippers take energy to manufacture and to run. It takes trucks and fuel to move chips around. There are a lot of chippers in the US and a lot of their output is treated as a waste instead of the valuable resource it can be to gardening and agriculture. Strategies to use whole woody material instead of chipping need more development. In the meantime chips should be preferentially used in horticulture. If industrial civilization goes down we will still be left with the non-chipping strategies which employ materials at, or near, the site of generation.
Tub grinders are built to grind up/chip large woody material such as logs, stumps, branches, construction waste, and pallets. Material can be ground fresh or dried. Big money to buy and operate these https://www.youtube.com/watch?v=izux01RBOKQ
Timber harvesting and forest thinning generates a lot of slash and woody debris. Hauling it long distances for garden or farm use is expensive. Consider instead the strategy of bringing agriculture to the woody biomass in the forest. Forest gardening. Making the hugelkulturs in the forest and plant semi-wild crop plants.
Ecosystem diversity = stability, resilience and productivity.
This goes for the garden too. The more habitats and microhabitats in the garden the better. A garden with logs, snags, woody material of various sizes and decay classes will have a higher level of biodiversity then gardens without such things. This is especially important for obtaining a high degree of fungal activity. This is one reason I like to use decayed wood in hugekulturs. Starting from scratch without any biomass it is going to take decades to centuries to get late-stage decay of large woody debris and associated organisms. Adding decaying, large woody debris to a garden immediately bootstraps this biodiversity.
Mushrooms. Many edible and medicinal mushrooms can be grown on various forms of woody material. Some specialize in colonizing fresh material, others at other stages of decomposition. For instance, fresh chip mulches in gardens can be inoculated with king stropharia, oyster and morel mushrooms. Getting another yield from wood chips while performing all it’s other ecosystem functions.
Wood chips, fines and ramial incorporated into the soil.
Tilling in chipped material has to be done judiciously. Mostly they should be applied to the soil surface. I have been tilling in chips for decades. I do this when I till a soil preparatory to putting in a long term agroforestry system. Most of my systems I only till once. How much to add depends on various factors, especially the level of soil biology and the amount of nitrogen. If the soil is relatively dead the chips won’t break down fast. This can be compensated for by adding soil inoculum when tilling. Generally I add manure, composts or nitrogen fertilizers (organic of course) when tilling in wood chips. This helps balance the carbon/nitrogen ration in the soil so the chip breakdown doesn’t tie up nitrogen
Feeding goats or other livestock with pruned wood and bark. One example is using goats to debark poles. I remember visiting a friend who had goats and he would fell small Douglas firs for poles and would let the goats eat the bark off the tree. After they had finished stripping the upper side he would turn the pole over so they could do the other side. This saved him the work of doing the pole-peeling and provided a lot of goat feed, which they loved. Another example from my homestead is when we pruned fruit trees we threw the prunings into the goat pasture and they stripped the bark and buds off with great gusto. We then picked up the peeled branches and used them in compost or for small stove wood. Now this is not keeping the carbon out of the atmosphere but it did lead to an additional yield from this underutilized resource. This is common practice in Africa and Asia but little used in the USA.
Hugelkultur Biomass Mound Technique
Michael Pilarski, Friends of the Trees Society
Hugelkultur (in its various spellings) is a traditional German technique developed long, long ago. Its name translates roughly into “mound culture”. The main aspect is to pile up rotting forest vegetation including logs into long mounds which are then topped off with soil and planted. It is, in effect, a long-term raised-bed. It becomes a high-fertility, well-drained, yet moist, sponge of biological activity. It is particularly appropriate for situations with poor soil, shallow soil (can even be built on pavement), heavy clay soils, waterlogged soils and areas with high rainfall and fast leaching of nutrients. Hugelkulturs are a good technique for places like the north shore of Kauai island which has high rainfall, infertile soils and organic matter quickly burns out of the soil.
They can also be used in dry areas.
A hugelkultur is a layered system. Many materials can be used, but predominantly it is forest biomass of various sizes from large to small. High nitrogen materials are needed as well as the final topping of soil. The final topping is ideally weed-free topsoil, but these two attributes seldom go hand in hand. Subsoil can be used, or topsoil with its seed bank, or finished compost or forest humus/duff layer or sand.
In some cases it is useful to dig a long trench first. Set any decent soil aside for the top layer. Or the pile can be built directly on top of whatever exists. A pit is particularly valuable in dry climates to enhance moisture retention. On waterlogged sites, pits are counterproductive as the bottom layer may become completely saturated and hence anaerobic and unavailable to root growth.
Most hugelkulturs built by hand are small and tend to be 6 feet wide at the base or so and 4 feet wide at the top and 2 to 4 feet high (and as long as materials allow). Large scale kugelkulturs built with heavy equipment can be quite large. Albert Postema of Snohomish Washington has built them 12 feet tall , 100s of feet long and 30 feet wide at the base. Large stumps and tree trunks are incorporated. Whole food forests are planted on them.
The largest material is placed on the bottom layer followed by consecutively smaller materials in the following order: logs, large branches, small branches, twigs, litter layer, duff, soil. Old boards can also be used, but avoid any treated wood. Most texts on the topic advise people to avoid cedar, eucalyptus, pine, walnut or other tree species which are known for their high levels of allelopathic substances. I have built hugels with high proportions of red cedar and they worked great from year one. I have friends who use ponderosa pine with good results.
It is important while building the pile that the voids between the woody biomass are filled with fine material. There are two reasons for this. 1) Nitrogen material has to be added to help balance the high carbon, woody material. The more rotted the woody material is the better. But fresh material can be used. The more rotted the material the better is the existing carbon/nitrogen balance. 2) We wish to avoid too many air pockets in the hugelkultur. Manure (fresh or composted) is the best high-nitrogen material to use. Seaweeds are also good as are any manner of green plant materials. Sod and seeds can be used deep in the pile, but not near the surface.. Kitchen wastes can also be used or what have you. Biochar is a useful addition.
The pile needs to be wet down as it is built if the materials are dry. The end result being like a moist sponge.
A well-built hugelkultur can be planted immediately after constructing. Hugelkulturs are usually used for high-value vegetables, herbs, etc. Large ones can also be used for shrubs, trees, etc. Because it is a labor and material intensive technique it is usually used in zone 1 or zone 2 situations. Hugelkulturs mature and improve with age. After a few years they store all the rainy season rainfall in its mass and can carry a crop through without irrigation. The interior becomes like a moist sponge but is also well aerated. Plant roots love the medium and can grow exuberantly. The nitrogen to carbon balance becomes better over the years. Depending on the climate and materials used the hugelkultur will be around and producing for decades. If the crop plants in the first year show signs of yellowing or N deficiency, apply a nitrogen-rich compost tea, manure tea, fish fertilizer or something similar.
Hugelkulturs are a productive way to use waste woody material which are too far gone for use as firewood or other higher-end uses.
Here are some resources:
See 5 of my hugelkultur videos at https://www.youtube.com/channel/UCylekw2DaAsQHsIWaR-js_A
Nice article with photos and links.
http://ecofarmingdaily.com/hugelkultur-gardening/
