Is Biochar Green?
Trapezoidal Kon-Tiki kiln design
In an e-conversation with a local Native American spokesperson, I asked why he was opposed to biochar production in Usal Forest, northern Mendocino County. Usal is a community forest, meaning that management is intended to support the local people and the forest itself, sustainably. He said,
[Biochar] is generally incompatible with respect for nature because it is based on assumptions related to valuing trees and forestlands as resources that can be perpetually extracted for profit. It [is] one of the methods used by industrial timberland owners and managers to “greenwash” their commercial harvest enterprises. It utilizes large-scale heavy machinery that produces lots of noise and very concentrated amounts of potentially harmful emissions. Its main purpose is to dispose of unwanted hardwood “weed” trees that compete with marketable conifers. If the hardwoods are removed, the conifers can grow much faster, resulting in more profits over shorter periods of time. After cutting them, an efficient way of getting the hardwoods out of the way and "cleaning up" the forests [is] to make biochar out of them.
There are much more ecologically beneficial methods of forest management that do not require biochar as a tool, but that can achieve some of the same objectives—including small-scale mosaic burns. But timberland owners would make less money using those methods.- Hawk
The conifers and hardwoods that Hawk refers to include Douglas-firs and tanoaks, respectively—the species that grow on my land. Since I’m restoring formerly logged land that Native Americans tended for thousands of years, I’m very interested in knowing what they would say about it.
good biochar gone bad
Hawk isn’t biochar’s only detractor. Tribal groups and environmental organizations have good reason to be skeptical of biomass conversion. Whenever biomass is transformed into a salable product, it becomes involved in the same economic forces that drive resource exploitation generally, which include scaling up for greater profit and greenwashing the result. These forces tend to push forestry toward monocultural plantations devoid of diversity and prone to destruction by wildfire. Seeing forests only as extractable resources is the original reason that fire and non-timber species were banished from their natural ecological roles. Biochar can be conscripted to serve this system by disposing of slash and “unwanted” hardwoods. In fairness to Usal, extraction is not their principal goal. However, a carbon-negative substance that also boosts soil health and productivity represents a world-class smokescreen for unsustainable practices. How can biochar production from forestry biomass be justified?
In reply to Hawk’s criticism, I stated that I am doing biochar a different way and for different reasons. While I’m not in a position to answer for Usal Redwood Forest Company, I can describe my own methods.
forest first
The way I’m doing it is to to make biochar from the excess fuel that’s resulted from over a century of complete fire suppression. Instead of favoring conifers, I am favoring oaks. I’m not logging, so there’s no extraction and no slash, although I’m preserving some of the straightest and most accessible conifers as timber trees for later. The only “weed trees” being killed to make room for commercially desirable ones are the conifers themselves, which are overabundant due to fire suppression. Neither is there major noise or pollution, because I am making biochar without heavy machinery, using a mobile kiln. Selective harvest of the few remaining firs, over time, will prioritize forest health. A great deal of my fir thinning is done by girdling, which minimizes disturbance and results in valuable habitat. Fuel reduction and thinning are aimed at improving the stand of mixed species, with biochar as a byproduct. The larger wood and most of the litter are left on site to feed the soil. The result will be a healthier, more diverse forest that can safely accommodate fire, which will burn close to the ground, releasing nutrients, and more water in the creek in summer, which benefits the salmon.
For a few years, all of my biochar went into the garden. Now I leave most of it in the woods. I could just incinerate the biomass beneficially, but making biochar helps the forest in ways that incineration does not. Biochar that you leave in the forest provides all the same ecosystem services that it does in the garden. However, it does not have to be inoculated and buried, as it’s done in gardening. Just spread it around as a top dressing, and it will gradually be charged with nutrients and incorporated on its own, as with any other forest litter.
I’m “cleaning up” the forest, but on different terms: I’m taking it back toward a condition that can safely include fire again. Douglas-firs behave like an invasive species under fire suppression. They grow up thickly in the understory, creating an unnatural "fire ladder” that threatens the entire forest with a canopy fire. They overtop the oaks and shade them out, displacing them along with the many ecological benefits they provide. Douglas-firs burn quite well while they’re alive. They are the principal contributor to the excess fuel load, but in the absence of fire, all species have added to it. I’m only cleaning up that mess.
teaming with biochar
Commercial biochar should have fairly consistent quality. But home gardens and forests don’t require biochar to meet particular standards of production. The biomass from which you make biochar can be whatever you have on hand. Multiple species and even partial conversion simply adds diversity to your biochar in terms of the ecosystem services it provides. Further variability results from uneven burn temperatures and “residence times.” But unless you’re marketing your biochar, this variability doesn’t matter. Whatever is not fully converted to charcoal is food for the soil. Diverse biomass and pyrolysis results in a diverse amendment, which supports a diverse soil fauna. This is another reason why big, expensive equipment isn’t necessarily needed. Flame cap kilns and conservation burns might not make perfect biochar, but they’re perfectly adequate if you aren’t selling the biochar. The standards that have been developed for commercial biochar can simply be a guide.
Biochar production can be unsustainable, but biochar itself is never a bad thing. When biochar is added to soil, water and nutrient retention, improved microbe habitat, and carbon sequestration all definitely occur. Biochar manufacture is not necessarily harmful, either. When properly done—in a top-lit pile, flame cap kiln, or retort—smoke is nearly eliminated. Half of the carbon contained in the biomass is sequestered for centuries, and the other half eventually would have returned to the atmosphere anyway. By only taking out the excess, overall forest biomass increases in the process, and it’s preserved by changing the fire regime to one that burns low and slow. Further benefits result from using the heat to displace heating with fossil fuel, where that is convenient. Sustainability depends primarily on whether biochar is made from excess fuel, resulting in a benefit to the forest.
the bigger picture
We have to reduce heavy fuel buildup before cooler fires that benefit forest health can occur. As long as we’re doing that, it makes sense to convert the excess woody material to something useful and divert carbon from circulation at the same time. Biomass in excess of the biosphere’s need for labile organic matter might as well be diverted to biochar, creating a valuable asset and contributing to the drawdown of atmospheric carbon.
But I believe that making biochar to deal with excess fuel and atmospheric carbon is mostly a transitional practice. The goal of fuel reduction is to eventually allow the “small-scale mosaic burns” that Hawk envisions. Apart from human needs for char and the broader ecological services it provides in the soil, taking carbon out of circulation is only helpful to the extent that the carbon cycle is out of balance. In the long term, biochar production should dwindle—still present, but not prominent—and be substantially replaced by fire on the land, where it belongs. As soon as fire can safely return to a landscape, the need for biochar to be manufactured on that land is vastly reduced. Making biochar is an excellent alternative to incineration when we have uses for the char, such as soil remediation and intensive cultivation, but it is not important in a healthy landscape, which in the West includes fire and the mosaic of diverse burn intensity that results from it. Biochar lasts for hundreds or thousands of years, so once a soil has enough, the overall demand drops. “Enough” is generally agreed to be about ten percent by volume in the top 18 inches.
Charcoal has many uses besides amending soil, and as fossil fuels decline we will probably find more ways to use charcoal in their place. To the extent that your soil is already healthy, you can put the charcoal that you make to other uses—including heating, filtration, blacksmithing, and construction. These applications may put pressure on forest resources locally, so they should be monitored for sustainability.
it’s about how
Whether or not biochar is “green” depends not on the biochar itself, but on the forest management system behind it. When your management plan is sustainable, so is your biochar. If trees and forestlands are seen as “resources that can be perpetually extracted for profit,” the fault lies in the system, not in the products. Even removing biochar from the forest isn’t inherently unsustainable. What matters is whether a surplus is maintained in the forest—of nutrients, of biomass. Blanket statements about biochar, for or against it, tend to be unsupportable. One has to define one’s terms, as I did with Hawk.
To which he replied, “right on Gray.”