Hugelkulturs and Carbon Sequestration

Hi. Pleased to meet everyone involved in this wonderful website.

I live in Springfield, MO, and am working on a proposal with two friends to get a few abandoned lots from the city to use as food forest space. We are trying to find information on how burying wood can increase the carbon sequestration and/or tie up carbon in the soil. Basically, we need someone to help us with explaining the science behind how hugelkulturs within a perennial food forest system can be a benefit to the environment, and specifically how burying wood can help. The reason we are focusing on (sunken) hugelkultur beds is that we are currently taking tree waste from local trimmers and using it in gardens instead of allowing it to sit in compost piles or be burned. We want to take more and put more tree waste, as much as possible into the soil, on a bigger scale, and we want to convince the city that it's a good idea to have these perennial polycultures instead of the alternatives of burning and composting. If anyone can help, we don't need a lot of ongoing support. Just enlighten us uneducated yet impassioned people!

Also, with the idea of a food forest in mind, and with 10,000 square feet per lot to work with for planting, while using sunken hugelkulturs, with access to unlimited wood and chips and brush, a backhoe, and a bobcat, where would you look in order to make the best decisions for design? Thank you so much for the help.

Ven

Burying the wood keeps the carbon stored in the trees to be locked up in the soil, thus not off gassing or combusting into atmospheric carbon (CO2, etc). If you are using exclusively chips I would look at something more along the lines of a sheet mulch or "Back to Eden" type garden system and planting your food forest into that. It is definitely doable on the 10K sq ft scale and might be a better use of your time and resources. Just spread the chips on top of the soil. If you have access to larger pieces of wood(like large limbs, stumps, or trunk pieces) then by all means go the hugel route. Hugelkulture is not always appropriate in every situation, evaluate your resources, etc. and utilize the best technique for your given environment.

Ven Wood wrote:Hi. Pleased to meet everyone involved in this wonderful website.

I live in Springfield, MO, and am working on a proposal with two friends to get a few abandoned lots from the city to use as food forest space. We are trying to find information on how burying wood can increase the carbon sequestration and/or tie up carbon in the soil. Basically, we need someone to help us with explaining the science behind how hugelkulturs within a perennial food forest system can be a benefit to the environment, and specifically how burying wood can help. The reason we are focusing on (sunken) hugelkultur beds is that we are currently taking tree waste from local trimmers and using it in gardens instead of allowing it to sit in compost piles or be burned. We want to take more and put more tree waste, as much as possible into the soil, on a bigger scale, and we want to convince the city that it's a good idea to have these perennial polycultures instead of the alternatives of burning and composting. If anyone can help, we don't need a lot of ongoing support. Just enlighten us uneducated yet impassioned people!

Also, with the idea of a food forest in mind, and with 10,000 square feet per lot to work with for planting, while using sunken hugelkulturs, with access to unlimited wood and chips and brush, a backhoe, and a bobcat, where would you look in order to make the best decisions for design? Thank you so much for the help.

Ven

hau Ven, carbon sequestering is done as Dave mentioned. Other good things also happen; Water is conserved since the rotting wood stores more water than soil alone. The microbiology of the soil will improve each year since mycorrhizal fungi will begin to sprout and form their wonderful threads, which will help plants grow better and healthier. Once the fungi fruit, more CO2 will be drawn down into the soil to be sequestered as well.

If you are going to be using mostly wood chips, then you have alternatives; Solid wood hugels with chips as part of the filler material, wood chip beds (the beds are covered at least 6" deep with wood chips which are then encouraged to decompose by watering with compost teas and infusions of green materials (grass clippings and pruned green leaves), Traditional Lasagna beds are created with the wood chips used as the base layer and then the mulch layer to hold in moisture, Hugel bed built with a huge wood chip base then covered with larger "whole" wood pieces then packed with a soil/wood chip blend, covered with a soil top coat and planted immediately. There are at least three more styles, each of which is a combination of two or more of the above alternatives.

In 10k "plots" you could have garden beds, raised garden beds, hugel mounds, interspersed with orchard trees (fruit trees) and/ or berry bushes, grape vines, etc. Orientation to the sun is the key, you want the sides of the mounds to be lit as much as possible on the south side (northern hemisphere) with the north facing side used for shade/ partial shade loving plants.

For tall and skinny mounds it is best to use the vertical wood method, this will allow you to have a 6' height and 6' wide base while still being able to keep the soil where you want it more than less. In this style, the tallest wood is in the center of the trench with each round heading out, away from the center logs, being shorter than the last.

It might be interesting to try to estimate how much carbon might be captured by burying wood. I bet if we searched we could find some numbers on how much carbon is contained in a ton of wood or a woodpile of specific dimensions. This winter I'll be helping my husband with a massive hugelkultur-like project of building brush dams aka leaky weirs in our creek to de-energize flood waters. The creek is cut into a channel 4 - 5 feet deep, and we plan to cram this full of wood for maybe 30 feet initially. That will probably be a couple tons of wood. Over time the wood will be covered by silt. We plan to continue down the channel in this manner as much as we can.

Here's a chart showing weights of wood by the cord: https://forestry.usu.edu/htm/forest-products/wood-heating

Carbon in trees: http://www.forestry.state.al.us/HowMuchCarbonHaveYourTreesStored.aspx?bv=5&s=0

Welcome to Permies, Ven Wood. Glad to have you with us!

I remember reading some articles from National Geographic on decreasing carbon content in soil. Yet, when I did a search I could not find them. Perhaps you will be more successful.
National Geographic also has an article or two on how perennials are better than annuals.

I used to work for the USDA. The USDA also has some good tools and references you might be able to use. The Web Soil Survey is one. I also remember the USDA puts out quarterly reports on a lot of topics. I used to get them emailed to my work email. Perhaps you can find the appropriate report and sign up for it. Most of the time they are free.

Perhaps contacting your local agricultural extension office too. Give him/her a call to see if they already have all the data and reports you want.

I've used my weak math skills to calculate that one cord of mixed hardwood and softwood, buried, can sequester 2.5 tons of CO2. Can someone else check this using the calculations here? http://www.forestry.state.al.us/HowMuchCarbonHaveYourTreesStored.aspx?bv=5&s=0

Tyler Ludens wrote:I've used my weak math skills to calculate that one cord of mixed hardwood and softwood, buried, can sequester 2.5 tons of CO2. Can someone else check this using the calculations here? http://www.forestry.state.al.us/HowMuchCarbonHaveYourTreesStored.aspx?bv=5&s=0

Hate to point out the obvious, but the carbon sequestration occurred when the tree sprouted from seed, grew and became that mighty tree. Burying the results merely transplants the carbon elsewhere. Hugelkultur will slow down the rerelease of the carbon to the environment thru various means but hugelkultur itself is not a sequestration technique. Planting a thousand seedlings of a fast growing plant species would be more effective, like say bamboo.

Here is the challenge: Which would be more 'sustainable'? 1) Cutting down the trees and building a log cabin. Or 2) doing the same thing and burying the trees in a hugelkultur bed?

If one builds and maintains a log cabin the carbon can be sequestered for more than a century. You bury it and over time a % of that carbon will be rereleased to the atmosphere over say a 50 year period.

Tyler Ludens wrote: This winter I'll be helping my husband with a massive hugelkultur-like project of building brush dams aka leaky weirs in our creek to de-energize flood waters. The creek is cut into a channel 4 - 5 feet deep, and we plan to cram this full of wood for maybe 30 feet initially. That will probably be a couple tons of wood.

Does that creek run off your property into some elses land? If so, are you prepared for the liability when that wood decides to up and move? Or your dam breaks?

You might be better off thinking metal-rock gabions. They won't up and float away and still act as a leaky flow and silt trap.

https://www.youtube.com/watch?v=ZvHkieDwnJo

john mcginnis wrote:

Does that creek run off your property into some elses land? If so, are you prepared for the liability when that wood decides to up and move?

It can't move onto the neighbors property, because there are many trees in the way. We can't do rock gabions because we don't have enough manpower to transport that many rocks. Just the two of us here.

john mcginnis wrote:

Hate to point out the obvious, but the carbon sequestration occurred when the tree sprouted from seed, grew and became that mighty tree.

The trees we're using are dead. I think less carbon will return to the atmosphere if the wood is buried. In my locale the usual practice to get rid of dead trees is to burn them in huge smoky piles.

Planting seedlings here doesn't work because they die of drought and/or get eaten by deer. We plan to protect native seedlings with brush piles and small fenced areas, but that is a long-term project.

"It can't move onto the neighbors property, because there are many trees in the way. "

I would suggest you calculate the tonnage a wall of water represents. I completed a swale berm 18" high against a 5 degree slope, 150' long recently on a parcel. Filled to capacity it would be 22 tons pressing against the berm. Your brush trap is going to collect sediment debris and the water level will rise over time. Same level of forces will come into play and at some point the trees may give way. Do as you wish, but I think you owe it to your neighbor to at least do the math and consider the liability to you should you be wrong.

Thank you for your concern, john. We've already made a couple brush dams and they haven't gotten even partly to the neighbors. We're thrilled with how they have behaved during the past couple of floods.

Article about burying wood as a carbon sequestration strategy: http://www.cbmjournal.com/content/3/1/1

I just read a bunch of that article, Tyler. It's got some interesting points to ponder and I didn't read it all but enough to get the gist throughout. I'm not sure that it really can be thought of in terms of hugulkultur because the author is concerned with long term sequestering of resources by eliminating decomposition of the wood, mostly in a anaerobic state. The author talks of burying the wood and then sealing the soil with wax at one point! He talks of actually creating anaerobic environments to prevent decomposition.

Some long term examples given to show the concept 1) that wood in landfills does not decompose (likely because it is dry, and less likely because it was buried under ideal conditions), 2) or trees under Ice Age glaciated areas (likely too cold and under too much pressure to decompose in spite of moisture, are neither really conducive to good hugulkultur!

The purpose of hugulkultur is not to sequester carbon, but to utilize the carbon as a nutrient sink to create soil. This is a short term carbon sink (as it gets bound to nitrogen), and as it builds communities with fungi, and other beings, which are in their turn carbon sinks. If one was to bury bio char, and cedar, and black locust, and other things that will stay in the soil a long time, that would be more likely to be a better carbon sequestering strategy.

I'm actually considering a carbon sequestering strategy by putting waste cedar down as a base layer (5 feet deep under my hugulkulturs) in some of my beds, with charred poplar, and biochar throughout the rest of the woody (rotten or dead wood) matrix of the mound, but the bio char is more for increased nutrient storage/biological activity, with the added benefit of long term carbon storage. Bio char and charred wood have a much greater chance of locking carbon in and stabilizing a long term hugulkultur then just burying rotten wood, while at the same time, being an effective medium for growing food.

To me, burying wood seems to be a fast strategy to get carbon into the soil. So to some people, the purpose of hugelkultur might be to sequester carbon, even though other people use it for other purposes. Getting carbon into the soil seems to be a valuable endeavor, in my opinion.

I completely agree with you, Tyler, and meant no disrespect. Getting the carbon into the soil is a valuable endeavor, indeed, and it does incorporate fairly quickly by burying it in a hugulkultur, but because it incorporates quickly it is not locked into a dormant state where the carbon is stored long term in the soil. A deeply buried cedar log, however, is a very long term carbon storage in relation to say burying a dead partly rotted poplar log in a hugulkultur. If that cedar is charred, it will last even longer.

The carbon from a regular dead log (that is not rot resistant, like cedar) in a hugulkultur does get into the soil, into the microbes, into the fungi. But then the wood decomposes. This is inevitable if you have a moist system of aerobic action as it seems you do from the descriptions of your hugulkultur. As the wood decomposes, and those fungi and microbes which facilitated the decomposition die, it then becomes CO2 in the gaseous systems within the soil and eventually into the atmosphere.

The carbon does become useful to the soil micro ecosystems in the meantime, connecting with other microbial elements in myriad ways including exchanges of sugars, and other molecules with the plants above, before the CO2 is released, but after the decomposition or death of microbes takes place, and the woody material has disintegrated into the soil system fully the Carbon is released into the atmosphere as CO2.

The only way to secure the carbon, would be in more woody living material. So, growing perennial shrubs, near the base on your hugul, or trees at or near the base on grade where they can feed off the nutrients in the hugul, might be a way to sequester some of the carbon, although my understanding is that most (the vast majority) of the carbon that is available for building a plant is taken in as CO2 through the chloroplasts in the process of photosynthesis.

That's how I understand it anyway.

The use of bio char, or charred wood, would make the process last longer. The carbon in those systems becomes part of the soil aggregate matrix more than it becomes available itself to the biological community for use as carbon for their microbial purposes.

The reason that I mentioned the Char:

The char is an aggregate in a more porous and cavity filled way than most aggregate like gravel or stone, and lasts considerably longer than wood left to rot without charring. The cavities within the bio char or in the charred parts of wood, have an incredible external and internal surface area that is charged with nutrient {liquid compost, manure, urine... etc} which thus turns char into bio char, instead of just char. The porous nature-all those little cavities and nooks and crannies-become a habitat where microbes can colonize safe from much predation, and fungi can network branching from one char nodule to another. From what I understand, the carbon is not itself as biologically available, though it will break down, becoming available over much greater spans of time (hundreds and possibly thousands of years, as evidenced by Terra Preta) than un-charred wood (which may last for 10 to 50 years maximum in a hugulkultur).

That is how I understand it. I may be wrong, and invite those with more knowledge to question my theory, and set me straight by expanding my understanding with more data.

I have seen people support the idea of planting grasses to sequester carbon, to return the carbon which was removed by plowing. It seems to me these grass roots would decompose as wood does - perhaps faster - yet grazing systems are promoted as a method of carbon sequestration. http://ecowatch.com/2015/01/26/farmers-rewarded-carbon-farming/ There is no living woody material in these pastures.

Hopefully anybody interested in hugulkultur for carbon sequestering is still reading this page. I'm thinking of starting a new thread. Please bear with the length. I apologize but do not know how to shut up.

What you say is true Tyler. What is happening with the grassland/grazing, (such as the holistic management system of Alan Savory), is that when a plant is grazed properly (that is: grazed to the point-but never beyond the point-of it's potential to maintain it's vigor, or to put another way: it's reserves and ability to regenerate fully are never compromised), the plants (perennial grasses, predominantly) do have a subsequent death of their root systems which corresponds with leaves which were grazed. These dead plant roots decay (and the microbes associated with the roots die, and the microbes involved in the decaying process die, and the fungi in a symbiotic relationship with the particular root also experience a die-off) and these all result in the gradual formation of humus, in the soil, which is black or dark brown due to richness in carbon from the decaying now dead micro community. If the grazing is done with holistically planned cell rotation, then the plants are not only grazed to the perfect amount, they also have their previous years dead woody stalks which are carbon rich (which would otherwise be left standing tall, high and dry from the soil microbes and thus be difficult to decompose) trampled into the ground, mixed with concentrated feces (carbon and nitrogen) and urine (nitrogen rich). The animals are then rotated out of the land into other cells. The land is left to fully recover (And they do with a vigor, since their regenerative capacity has not been compromised, and in many cases is actually greatly stimulated). from this multiple impact and enriching with nutrients before the animals are allowed to return to the particular cell. The quantity of land, the amount of rainfall, the distribution of rainfall over time, the quantity of cattle/or other ungulate grazers, and observation of the plant's growth patterns, all contribute to the management plan (specifically figuring out when to return the animals to a given cell after grazing.)

The article you mentioned does not really get into the specifics of this, but mostly mentions farmers leaving existing meadows out of their tilling regime, and thus keeping the humus layer intact, which conserves the carbon that is trapped in the soil. That is true to a degree, but would be considerably better at carbon sequestering under proper cell grazing.

Tyler, I'm grateful for you questioning my reasoning, and giving me that article to ponder; it really made me think hard and search for answers both in my mind and on the internet. It sent me in a good direction, as I continued to search after reading it. The link itself did not do much justice in describing what is actually going on, unfortunately, but I'm grateful for it. I did find this amazing site, in my further search for answers. It gave a pretty serious contribution of data:

http://www.nature.com/scitable/knowledge/library/soil-carbon-storage-84223790


Here are 12 direct quotes (in the order that they appear in the article) which I will then comment on as briefly as possible (XXX). Some lead to further questions and possibly some answers, which I will either leave to everyone to ponder, and\or comment on myself. All underlining was done by me to emphasize what specifically about the quote is important (in my opinion) and in two cases I've used bold type as well to further emphasize.

1.)"Benefits of soil organic matter (SOM) include improvement of soil quality through increased retention of water and nutrients, resulting in greater productivity of plants in natural environments and agricultural settings." XXX Hugulkultur, as it breaks down, from all the understanding I can glean from the broadcast seeds of those expert in it's workings, increases water and nutrient retention. Awesome. Yay hugulkultur! But I would also say that this is also true of biochar and over a much longer period of time per unit of carbon.

2.)"Soil organic matter is composed of soil microbes including bacteria and fungi, decaying material from once-living organisms such as plant and animal tissues, fecal material, and products formed from their decomposition. SOM is a heterogeneous mixture of materials that range in stage of decomposition from fresh plant residues to highly decomposed material known as humus. SOM is made of organic compounds that are highly enriched in carbon. Soil organic carbon (SOC) levels are directly related to the amount of organic matter contained in soil and SOC is often how organic matter is measured in soils." XXX This organic matter clearly includes the wood in the hugulkultur, but only after it has begun to decay into the soil system through micro-biological processes. The last part of this quote makes me wonder... if the majority of hugul wood does indeed break down to form humus/blackish soil then it would be included in SOC levels. I don't know if it is know if this is the case or not.

3.)"SOC levels result from the interactions of several ecosystem processes, of which photosynthesis, respiration, and decomposition are key."
XXX As I mentioned in my previous post. I won't repeat.

4.)"Photosynthesis is the fixation of atmospheric CO2 into plant biomass. SOC input rates are primarily determined by the root biomass of a plant, but also include litter deposited from plant shoots. Soil C results both directly from growth and death of plant roots, as well as indirectly from the transfer of carbon-enriched compounds from roots to soil microbes. For example, many plants form symbiotic associations between their roots and specialized fungi in the soil known as mycorrhizae; the roots provide the fungi energy in the form of carbon while the fungi provide the plant with often-limiting nutrients such as phosphorous." XXX I commented on this in my previous post as well.

5.)"Decomposition of biomass by soil microbes results in carbon loss as CO2 from the soil due to microbial respiration C, [u]while a small proportion of the original carbon is retained in the soil through the formation of humus[/u], a product that often gives carbon-rich soils their characteristic dark color" XXX I did not take into account in my previous post that the humus retains the carbon over a long period, and this was a very important omission on my part. I had assumed that the carbon was eventually respired as CO2, and since that only happens when the soil is disturbed by tillage or exposure to high heat, a good hugulkultur which is not disturbed may very well trap a good deal of carbon in the soil itself.
XXX I think this is the most important part that I was trying to get across in my previous post, though now that I've read this article, I'm not entirely sure what the fact of the matter is. I elaborate now: While a hugulkultur is decomposing, my assumption is that a great deal of microbial respiration takes place. This may not be true, but that is what I assume to be true through my understanding. However, the amount of a hugulkultur which actually becomes humus in relation to that which is being respired by microbes remains to be seen, as far as I know. Also, as far as I know, no scientific studies and dissections of long term hugulkultur exist to prove or disprove the amount of humus that is actually produced from a given amount of carbon, or how much carbon is exhaled (respired) in the form of CO2; And this leads to the next quote.

6.)"These various forms of SOC differ in their recalcitrance, or resistance to decomposition. Humus is highly recalcitrant, and this resistance to decomposition leads to a long residence time in soil. Plant debris is less recalcitrant, resulting in a much shorter residence time in soil." XXX What this means in terms of a hugul's wood is a BIG ? as far as I know. Does the wood become humus, and then become highly recalcitrant?-That would be awesome, and would definately be a massive boost for hugulkultur as a carbon sequestering powerhouse. But if the hugul wood's carbon is included in the concept of plant debris, as is boldly underlined in the above quote, then it seems like it is mostly respired, which is sad for hugulkultur's ability to store carbon on a long term scale, and is more of what I assumed in my previous post. It remains to be known, unless someone with more information / science about hugulkultur's carbon sequestering potential can pipe up.

7.)"When carbon inputs and outputs are in balance with one another, there is no net change in SOC levels. When carbon inputs from photosynthesis exceed C losses, SOC levels increase over time." XXX The question here, in my mind is: Could the wood in a hugulkultur be included in the carbon inputs from photosynthesis? I think that this is very possible, but is not understood/ known. I believe, that like the Pacific Northwest Coastal Temperate Rainforest, the massive gains of rotting wood in a hugulkultur particularly in Temperate climates, is quite potentially the greatest source of carbon sequestering that can be accomplished in places where hugul wood is readily available. But, again, this remains to be known for certain, if this is long term carbon sequestering in humus, or if most of the carbon is predominantly doomed for atmospheric bound microbial respiration.

8.)"While the carbon released to the atmosphere through deforestation includes carbon emitted from the decomposition of aboveground plant biomass, carbon levels in the soil are also rapidly depleted from the decomposition of SOM. The decomposition of SOM is due to the activity of the microbial decomposer community in the absence of continual rates of carbon input from the growth of forest vegetation, as well as increased soil temperatures that result from warming of the ground once the forest canopy has been removed. Although this soil carbon loss has contributed to increased CO2 levels in the atmosphere, it also is an opportunity to store some of this carbon in soil from reforestation." XXX Here is the place for both hugulkultur and buried biochar, and other permaculture/organic horticultural/food forestry/and holistic forestry techniques to possibly make big gains, but to what degree with any given technique remains to be known. The mention of aboveground plant biomass in this quote leads to some question as to what happens if the plant biomass is buried. Possible gains for hugulkultur (?)

9.)"Current estimates are that carbon inputs from photosynthesis by terrestrial vegetation fixes more carbon than carbon loss through soil respiration, resulting in a soil storage rate of about 3 GT C/yr." I'm not sure what to make of this last statistic, but it is hopeful as a case builder for hugulkultur that if more carbon is being fixed by photosynthesis than through soil respiration, AND the wood in a hugulkultur is included in photosynthetic gained carbon in the soil, rather than included in plant debris in the soil as mentioned in quote 6, then hugulkultur gains big. Again, as far as I know this is an unknown variable.

10.)"The goal of increased storage of carbon in soil has received much wider acceptance due to a better understanding of the processes involved in SOC storage, more direct control of these processes through human activities, and the other known ecosystem benefits to be obtained by increasing SOC, including benefits to water quality and increased food security." XXX Here, they are comparing deep oceanic carbon storage to terrestrial storage. I do not think they are talking of carbon sequestering due to burying wood, but through planting trees, and leaving soil systems intact. What this says to merit the various ideas bounced around in these permaculture forums remains to be either understood or voiced on this particular site. Hopefully we can change that, as these folks seem like they have a lot of knowledge, and it would be good to have it tooting the permaculture horn.

11.)"Soil Carbon Sequestration
Soil carbon sequestration is a process in which CO2 is removed from the atmosphere and stored in the soil carbon pool. This process is primarily mediated by plants through photosynthesis, with carbon stored in the form of SOC." The question, again, is: Does the wood in a hugulkultur count as a photosynthetic produced soil carbon pool addition, or is it plant debris?

12.)" ...the conversion of natural ecosystems to agricultural use has resulted in the depletion of SOC levels, releasing 50 to 100 GT of carbon from soil into the atmosphere (Lal 2009). This is the combined result of reductions in the amount of plant roots and residues returned to the soil, increased decomposition from soil tillage, and increased soil erosion" XXX So we definitely need to rethink our food growing systems if we want to reduce carbon emissions, and I believe that hugulkultur potentially has a huge role to play, but, in my opinion, biochar (particularly if made in the winter and the heat from the wood burning and pyroletic conversion in the creation of the char is utilized to heat a home) is a much better carbon sink for long term storage, IF the carbon from a hugulkultur wood is not predominantly converted to humus. IF the reality of hugulkultur breakdown is predominantly humus forming rather than respiring carbon, then clearly hugulkultur wins the debate for long term storage, and less work.

13.)"Depletion of SOC stocks has created a soil carbon deficit that represents an opportunity to store carbon in soil through a variety of land management approaches. However, various factors impact potential soil carbon change in the future, including climatic controls, historic land use patterns, current land management strategies, and topographic heterogeneity." XXX Permaculture to the rescue!!! Hugulkultur Anyone? Indoor biochar reactors, perhaps?

If you made it this far, then i'm super grateful. Thanks, huge. I hope it was helpful in understanding my brain. There is a lot here, and I apologize for it's length. I hope this can show both my curiosity and my attempt at both hypothesizing the merits or lack thereof of hugulkultur's carbon sequestering potential and unbiased questioning of the data presented thus far to me.

I guess that's 13, not 12. lucky number, that.

It seems like quite a bit rests on whether or not the buried wood in hugelkultur would be categorized as plant debris or not. For what it's worth when I read "plant debris" (#6) it seems to me that would be the residual remains of the photosynthesizing growing areas of the plant (i.e. the top side growth) left to decompose on or near the surface. That's just how I read that statement, and it makes sense to me that way. That part of the plant left in that area to decompose wouldn't add much to the humus layer. Thinking of it another way: all of the plant would be considered "plant debris" and there would be little to no humus creation in this scenario otherwise. I think we can agree that this is not the case, based on the successful, measured and documented SOC increases in systems that utilize Holistic Management or other soil building grazing practices. It seems as though you could extrapolate that line of thinking to include buried wood in the same category as rotting root masses that go into creating the humus content of our soils.... hugelkutur creates humus rich soils as the wood core breaks down. Anecdotal evidence from the likes of Sepp Holzer indicate that once the wood core has fully decomposed and the mound is broken down to be rebuilt you are left with the finest, humus rich soil you can imagine to create new growing areas from. Holzer has been utilizing hugelkultur for this for decades with excellent success.

Oh well that's my two cents worth, and how I read and interpret the information you provided above.

Dave Dahlsrud wrote: It seems as though you could extrapolate that line of thinking to include buried wood in the same category as rotting root masses that go into creating the humus content of our soils.... hugelkutur creates humus rich soils as the wood core breaks down. Anecdotal evidence from the likes of Sepp Holzer indicate that once the wood core has fully decomposed and the mound is broken down to be rebuilt you are left with the finest, humus rich soil you can imagine to create new growing areas from. Holzer has been utilizing hugelkultur for this for decades with excellent success.

That's what it seems like to me as well. Do hugelkultur or buried wood create humus (sequester carbon)? I think the evidence indicates they do. Are there more effective (and difficult) methods of sequestering carbon using wood? Possibly, and there are other threads about that.

And an entire forum : https://permies.com/forums/f-190/biochar

I do realize that Sepp says the soil coming out as he is breaking up long term hugulkulturs is humus rich. Sorry that I did not include that observation of his conclusion. I guess the thought that I have about that, is that it would be really cool to know how much of the hugul wood mass itself has been translated to humus {rather than whatever else is incorporated mounds in the building process, and also including all the roots of the plants that are growing on the beds over all that time), and to have it actually scientifically analysed for it's carbon content, if it's possible to know where the carbon originated. I don't know if that's possible. I mean Sepp is awesome... amazing... incredible really, in so many ways, and so it's hard to say that he might not actually be bang on (with his analysis of the humus creation from the wood... I don't have the books, although I've read two of them and have watched a few videos with him so I can't recall if he simply says that the hugul beds themselves became humus rich mounds of soil, or did he say, fundamentally that the humus was created from the carbon in wood?). Maybe I'm just playing devil's advocate here, but it would be nice to have his statement understood fully, and verified by some hard science to be sure of what is actually happening. I'd be super curious to know.

It may very well be that the hugulkultur wood does translate to humus creation, but it is possible that the carbon from the wood matter becomes largely transpired CO2, while being used as a medium for nutrient and water storage, and microbial/fungal habitat. Microbial/fungal habitat in itself, I must concede, might be enough to lock that woody carbon into the humus. I hope that the latter is the case, because that would be most beneficial.

I'm going to take this opportunity to reiterate the idea that I posted earlier on this thread (and seemed to be verified within this article, and in the link that Tyler posted) that breaking up the hugulkultur to rebuild it would create a loss of carbon to the atmosphere. It would be better to just add material and keep the biome of the mound intact.

Also, it was in my thinking that the hugul wood might be included in the same category as the dead root mass of plants, although I did not say that specifically, as I was (whether anybody can believe it) trying to limit the length of my own comments, and I was, perhaps focusing more on the underlined part of quote 5 (since the wood material in a hugulkultur is certainly biomass) to understand quote 6. While not trying to take away from the benefit of your extrapolation, which I think is valuable and has merit, Dave D, as far as this, or any other theoretical topic of conversation, a person can extrapolate in many different directions but gain little on the hypothesis without a controlled experiment. That said, my own extrapolations and conclusions are in the same boat.

My understanding of humus, in relation to the dead root matter, is that it's the microbes, which died in direct or indirect relationships with the woody material and the fungi impregnating the structure of the roots dead or alive, which have absorbed some of it's carbon and then died themselves, that actually become the humus. I may be wrong. I just don't know how much of the carbon in a plant's roots-which are dead and decaying in the soil-is actually respired as CO2 into the atmosphere, rather than actually being incorporated as humus. My understanding is that it is the carbon in the dead microbes that become humus, not directly the carbon from the woody root materials (which is largely respired, according to the article.

The voluminous communities of microbes and fungi that are inherent in a hugulkultur's biome at maturity which have died to become a massive store of humus, and thus result in SOC gained through the use of hugulkultur, and that is a great gain. So perhaps most of my questions, then, become irrelevant.

Roberto pokachinni wrote: breaking up the hugulkultur to rebuild it

Breaking up a hugelkultur to rebuild it seems a bizarre idea to me and I don't know why anyone would do that rather than simply add more material to it (or, perhaps better, leave it alone and grow trees on or next to it).

Some interesting items:

"Within soil horizons, some species of wood are more persistent than others, especially pines, larches, and Douglas-fir, which decompose largely to a “brown rotted wood” condition. These have very high persistence times within soils, as they have high lignin content that resists decomposition. This means that their beneficial function as reservoirs as moisture, mycorrhizae, microbes, and nutrients can last for decades and centuries."

http://www.fs.fed.us/r6/nr/wildlife/decaid/pages/Ecosystem-Processes.html (article is about down wood and stumps, not buried wood per se)

"Lignin metabolism is of utmost importance to the carbon cycle on earth. As a major structural component of photosynthetic biomass, lignin makes up approximately 25% of the dry weight of vascular plants and is second only to cellulose, which accounts for about 50% of the dry weight of cellular carbon stored in the biosphere. However, lignin stores more solar energy and hence accounts for more fuel value in wood than does cellulose because of lignin’s unique chemical structure. Lignin is nature’s most abundant recalcitrant product."

http://link.springer.com/chapter/10.1007/978-1-4615-8306-6_5

Breaking up a hugelkultur to rebuild it seems a bizarre idea to me and I don't know why anyone would do that rather than simply add more material to it (or, perhaps better, leave it alone and grow trees on or next to it).

I completely agree; breaking up a hugulkultur to add wood and rebuild it using that previous hugulkultur material to cover it doesn't make sense, but from what I gather, that is what Sepp does when the hugul loses much of it's structure. The only good I can see from doing this is the inoculation aspect, but this could be done more easily and with a small amount of the material (a shovelful), if spread via AACT Actively Aerated Compost Tea (Everyone should read Teaming With Microbes!). When I did the permablitz in Darfield, Javan (who spent a bunch of time with Sepp) suggested that the owners could, in the future, choose to dig up the reserve of broken down woody material as a source of nutrients. It wasn't something that he said they should do, but something that a person could do, which is fair enough. It's good for him to put ideas out there, so people expand their bubble of possibilities. For sure, one could do that, but I can't fathom wanting to do it, considering how much more of an amazing resource it is as a unified community-a special place of diversity and growth-than it is as a resource to mine. Interestingly, it was at this same permablitz that I had my first experience of building a hugulkultur and using AACT.

Awesome links, Tyler ! Too bad the second link was only an abstract to the chapter, though; and to get at the chapter proper, or the book, one has to pay.

Your first quote is great news indeed. I'm glad to be proven wrong. Particularly considering I have pine and douglas fir on my property! Also, the first link might help me to convince the local community forest to not burn slash, but to lay it on the surface, or better yet try hugulkulturing it.

Thank you, Robert, you've challenged me to dig further for information. But I think the estimates I posted for hugelkultur carbon sequestration may be too high, because there will be loss of carbon from decomposition of cellulose (less from lignin). If one is burying wood with the primary purpose of sequestering carbon, it might be better to estimate on the low side - and make more hugekultur.

Tyler, I too enjoyed the challenge of figuring this out. I thought there were times where I was annoying the manure out of you, and I hope you know that that was never the intent. I tend to speak my mind and shoot rapid fire from the hip, and that can get me into trouble, but, particularly on Permies, I try to temper my words with a bit of reserve; not that I don't think people here can't handle it, but because I'd rather make friends than be an incendiary ass. I think that your honest pursuit of things hugulkultural and hopes at carbon sequestering in this manner are definitely full of promise. I follow your posts (and great photos) because of your insight and your ability to question yourself and, and allow yourself to be alright with how something turns out, even if it's not how you wanted it to be, or to not be perfect the way you thought it might be (and posting pic's of that too!) and the ability to move forward throughout the learning process. I hope that one day soon some one adventures toward studying hugulkultur in a serious way, so that these answers might be known unequivocally. However your statement that we should just build more hugulkultur to make up for the carbon loss from the CO2 respiration of cellulose eating microbes is wise. The world definitely needs more hugulkultur, and a little bit of CO2 from us doing so is hardly an issue worth mentioning when you consider that the 15 largest ships on the ocean cause more greenhouse gas emissions than all the cars on the planet. Think of the good you are doing ecologically, and move forward. In growth, in the spirit of learning... my all your seeds sprout and bear fruit.

Thank you so much Roberto. I know the feeling of passionately wanting to get at real facts!

What matters with regard to climate change is the net flux from stable to active carbon cycles. Basically we are talking the stable soil carbon fraction and fossil fuels as the stable pools, and the rest of the carbon that cycles actively is just part of life cycles. There are frozen methane clathrates in the ocean and permafrost that can be a concern should they melt rapidly, but that's more of a feedback concern, if we fail to get the other pools stabilized. More of a symptom that magnifies, not an initial cause. This is one of the things, that if it happens, will dramatically amplify the seriousness of AGW.

Any agriculture of any type that increases the stable carbon pool in the soil is not creating AGW, but rather is helping mitigate AGW. So the question really is how much of the wood (active fraction) converts to humus (stable fraction) when buried in the ground as opposed to rotting on the surface. I wish I knew that answer with actual numbers from a scientific study, but I really haven't seen one. I can say with pretty good certainty though that burying the wood will increase the sequestration potential substantially. In a similar way grassland are actually better at sequestering carbon than forests. Forests do take the early lead with greater biomass than grasslands, but that biomass is only temporary and once mature a forest becomes carbon neutral. But grasslands sequester carbon deep in the soil with root exudates instead of in biomass and that carbon once broken down into stable form lasts thousands of years. This explains why the O-horizon on a forest floor is much larger than a grassland O-horizon, but the A-horizon of a grassland is many many times larger. The O-horizon is mostly active cycle carbon, but the A-horizon is 30-50% stable carbon pool and will last thousands of years as long as it isn't disturbed.

This scientific study explains it. Grassland cooling

Now of course there are other reasons for sequestering carbon than climate change. In many of those cases the partially decomposed active fraction is equally beneficial as the stable pool. For example in holding water.

Ven's original post indicated an interest in providing free food to his community by reclaiming a lot of lots. That's pretty much identical to my interests in Pine Bluff, Arkansas, which today is nearly as bleak and painfully hungry as Detroit.

Sequestering carbon has practically no bearing on the crux of Ven's objectives, presuming they still stand. Using Hugelkultur in this particular situation is beneficial on several levels, few of which were even considered by the majority of readers on this thread. "Experiment," seemed to be the most promising suggestion of the bunch.  

Hi Tom-Scott,

So when I read Ven's original thread starting post, I focused on this quote:

We are trying to find information on how burying wood can increase the carbon sequestration and/or tie up carbon in the soil. Basically, we need someone to help us with explaining the science behind how hugelkulturs within a perennial food forest system can be a benefit to the environment, and specifically how burying wood can help.

 While, in your view, the carbon sequestration question may have no bearing on the project, Ven was looking for data or facts, or ideas pertaining to this in order to convince bureaucrats. That seemed to be the quest that Ven was on, and I think that that is what was explored in the discussion, if I remember correctly, and via a brief skim seems to be accurate; though I'm not now going to read the entire thread's contents again at the moment, I think that you will find that that is the case.  I think that there was a great deal more than the suggestion for Ven to experiment in this thread, and there was quite a discussion about carbon sequestration.

Certainly there are other potential benefits of hugulkultur, and many of these were and are available to search and discover on this site's hugulkultur forum.

If you have some other suggestions which may further enlighten the cause, please feel free to continue the thread, or start a new one with your insights, or further questions.

Happy Permaculturing, and good luck with your projects.  

A food forest in any city would be great! Sets a much needed positive example as well as gives a therapeutic space within an anti-therapeutic (stressful) one. But as far as carbon sequestration is concerned I believe it's token or negligible, at least compared to the vast potential of growing microalgae. At least when grown in urban space or some other desert, so as not to displace food cropland for fuel. Not only is microalgae the fastest growing plant in the world (so is fastest at making oxygen as well as consuming carbon) but can be grown to become lipid (fat/oil) heavy for fuel or food. I believe it creates...oh well, just read this: https://www.realnatural.org/algal-dha-lowers-triglycerides-vldl/  Anyways, it's brain healthy for both aging adults as well as for brain development in children. OgreNick

Great thread guys...Tyler and Robert, your thoughts have brought to mind what I read in Noss' Redwood Ecology text:

The rate of decomposition is inversely proportional to the retention of carbon and nitrogen in the soil.

I interpreted this to indicate that the extremely slow (upwards of 2x the life of the tree) but efficient decomposition of redwood is a big part of why the coastal redwood forests have the highest biomass on Earth by a large margin. This biomass over 50% more than the closest other terrestrial ecosystem (in Hoh Rainforest of Olympic NP), and 5-10x that of a tropical rainforests where decomposition is rapid. Alongside the slow decomposition of the redwood (which is really great for growing redwood and things that redwoods benefit from but not much else), is a plethora of other, faster decomposing biomass. This must create edge effects abound, and may be why the soil life in these ancient forests is the most diverse known (again, my memory of Noss), with 15,000 soil invertebrate animal species/m2 in some measurements.

My hypothesis is that the fact that available Nitrogen is the limiting factor for maximal biomass in these forests (again, Noss) has selected for this slow decomposition dynamic in the redwood ecosystem, as the immense biomass of these forests is how they keep enough water in the system to remain catastrophic fire-proof despite dry summers. The lushest parts of the redwood coast have no history of catastrophic fire. The ecosystems that got past a tipping point of biomass to environmentally self-regulate through their own fog and rain creation and temperature moderation became fire proof. Those ecosystems had to have trees with tannins potent enough to slow decomposition to the point where it became extremely Nitrogen efficient and rich in nitrogen fixating plants and fungus. Tadaa... Redwood forests!

In regard to the question of sequestration it seems like hugelkulture is analogous to a safe, high-return short term investment that can form the foundation for a longer term investment strategy. The carbon forms the anchor/sponge for all the other components of humus to latch on to, and in turn grows plants and fungus that sequester more carbon and nitrogen and produce more organic matter for more hugel.

Be sure to join Paul for a presentation all about hugelkultur!!!

February 25th at 10 am Paul will talk about all things hugelkultur and answer questions.

get access here:  https://permies.com/wiki/203182/Webinar-Hugelkultur-Paul-Wheaton

If you have large amounts of high carbon materials you wish to turn into a growing medium, hugelkultur seems ideal. Especially if the materials have a lot of lignin. This is because lignin is broken down by fungi. You want the decomposition to be fungally dominant to make the lignin bioavailable. It isn't necessary to try to speed decomposition in my opinion. If you want compost, make a hot compost, this is different. I have been building mounds in my backyard for about 30 years. I get materials to dispose of in batches that are usually high carbon. It would be a lot of extra work to source nitrogen to add and then the turning. I simply put down a layer about 18 inches deep and cover it with about 4 inches of "soil". I use the quotes because this isn't ordinary soil it is mined out of my oldest mound. I build the mounds by hand so I only go about 6 feet tall. As it settles I add more layers. When I break down an old mound the inside resembles potting soil with bits of wood in it that are completely colonized with mycelium. Sometimes a chunk of old firewood has been broken down by brown rot, it looks just like peat moss. As I break the pile down I do a little sorting. There will be pockets that are obviously not done. These get added to newer piles, innoculating them with organisms that love carbon. Some that looks more finished gets sifted to remove any pine cones, stones etc. that aren't wanted. These go on a new pile. The sifted product I use in my lawn business. I also plant a vegetable garden inspired by my permaculture reading. In the autumn I sheet mulch the garden with about two feet of leaves. In the spring I pull the mulch aside and broadcast my seeds on the surface in 4 by 4 squares with several types of plants mixed together. I cover the seed with the soil from the mound I am currently breaking down. I also start some plants in pots to fill in any empty spots. The soil from the mounds is much looser than my local clay soil but not nutrient dense. The secret is that it is alive with organisms that can take nitrogen from the air and make it available in the soil. I think of the soil from my mounds as habitat for the living organisms who will provide the fertility.