wood pyrolysis

(Note: This is the final post in a brief end-of-the-year series on marijuana cultivation. After this series is over, GeoCurrents will take a short break. More conventional posting will resume by the middle of January.)

As is explained in a previous post, most marijuana growing currently carried out in California and neighboring states is environmentally destructive, generating a gargantuan carbon footprint. But it need not be. As I have learned from interviewing small-scale growers in northwestern California, the cultivation of cannabis can be done in an environmentally benign manner. The problem, as these producers see it, is the fact that neither the marijuana market nor the environmental movement gives them any credit for their efforts. They persist nonetheless, with the more devoted among them trying to figure out how to reduce their impact as much as possible.

The purpose of this post is merely to provide the perspective of a small group of individuals engaged in an interesting and legally nebulous* activity, not to advocate on their behalf. My own eco-political viewpoint, it is essential to note, deviates markedly from theirs. I adhere to the philosophy of eco-modernism, which holds that environmental protection is best achieved through continuing economic growth and technological progress, whereas they tend to be eco-romantics, skeptical of—if not hostile toward—both high technology and untrammelled economic development.

It is also important to note that although my interviewees all consider themselves ardent environmentalists, they themselves deviate from conventional green thinking, most importantly by veering toward a form of left-wing libertarianism. As is common among rural property owners, they are not opposed to the notion of property rights, and they generally think that they should be able to do they think is best on their own lands, allowing for reasonable exceptions. As a result, they are not fond of land-use restrictions and permitting regimes, and they are happy that the county in which they live is quite relaxed about such issues. Most of them also own guns, drive trucks, ride all-terrain vehicles, use chainsaws, and do not hesitate to employ heavy earth-moving equipment. Their culture might best be described as an unlikely hippie-redneck synthesis, which is precisely why I find it so fascinating. But unlike either the stereotypical hippie or redneck, these people tend to be well-read and highly intellectually engaged.

Environmentally conscientious growers are helped by the fact that cannabis is a hardy plant that is not particularly troubled by insects or other pests. To be sure, in greenhouses and indoor cultivation facilities, some pests can multiply uncontrollably, especially spider mites. But the growers I interviewed claim that in their operations this is almost never a problem. They did mention a few minor issues with leafhoppers and caterpillars of unknown species, but they also maintain that manual removal is adequate to keep their populations in check (small-scale growers typically lavish extraordinary attention on each plant). Their only real problem is bud-mold during the maturation period. Some spray neem oil on their plants during the earlier vegetative stage to reduce mold infestations, but once the buds have started to form the only remedy is manual removal followed by the spraying of alcohol to thwart further spread. Disagreement about the efficacy of this technique, however, is pronounced.

As mentioned in previous posts, one of the major forms of environmental damage associated with outdoor cultivation if the use of rodenticides to control woodrats. My informants again insist that this is not an issue in their operations. Woodrats do not actually eat cannabis plants, they told me, but rather use the stems for nest building. One grower admitted that he had had a rat problem in his first year of operation, but after one season of concerted trapping he no longer suffers much damage. Separating gardens from the surrounding woods and meadows with stout redwood fencing, a precaution demanded by the county, also seems to help in this regard. Fencing also prevents harm from feral hogs, which can otherwise be a huge headache. Hogs do not eat the plants, but they do root into the irrigated soil for worms, causing extensive damage.

Although outdoor marijuana growing is vastly less carbon-intensive than indoor cultivation, it is certainly not carbon free. Everyone that I interviewed pumps water from wells, as cannabis is a water-demanding crop and the area in question has a Mediterranean climate with a rainless summer. One grower hopes to install solar panels to operate his pump, and another outlined a scheme for storing runoff during the rainy season, but as it now stands, they all use either grid-delivered electricity or fossil-fuel-powered generators. In the harvest season, the dehumidification of drying rooms is also necessary. In a year such as 2014, when the initial rains were relatively warm, dehumidification can be a major energy drain. During this season, intensive illumination is also required for trimming crews during the evening hours.

Even larger energy expenses are encountered among those who plant clones rather than seeds. Clones have one huge advantage over seeds, as every plant is guaranteed to be female, and males are worthless. The main problem with clones is that they cannot be grown exclusively under sunlight until late May, which reduces their growing time and therefore limits their size. This restraint stems from the fact that clones are obtained from indoor growers who keep them under light for 18 hours a day; as cannabis flowering is keyed to day length, if a clone is planted when the nights are still relatively long, the plants will prematurely bud. As a result, even outdoor growers sometimes augment the sun with artificial illumination for the first few weeks or even month of the growing season. Even more energy-demanding is the greenhouse-based system of light deprivation, which requires especially early planting but allows especially early harvesting, the latter achieved by artificially reducing day-length in the early summer with opaque coverings. But according to the more environmentally fastidious growers, “light dep” is halfway to indoor cultivation and is therefore to be shunned.

Some of those who grow by seed disdain the entire cloning procedure as unnatural. They further argue that clones are often weak, especially if they are derived from old mother-plants, and that even in the best of circumstances they never develop proper taproots. The main problem faced by those who grow from seeds is the fact that roughly half of their plants will be males, which not only must be uprooted and discarded, but which can also contaminate an entire crop if they release pollen before they are detected. Daily vigilance is needed to avoid this potential disaster. To remain within the county’s 25-plant limit throughout the season, such growers are therefore restricted to some 12 or 13 plants in the end. Some purchase expensive “feminized seeds” to try to increase the ratio of females to males, but the efficacy of this technique is also much debated.

But if carbon emissions are an unavoidable consequence of the cannabis production process, some growers nevertheless think that their operations can be carbon neutral or even carbon negative in the end. The key procedure here is carbon sequestration, accomplished by burying charcoal the soil. Charcoal used in this manner is called biochar, which is defined by the Wikipedia as:

a name for charcoal when it is used for particular purposes, especially as a soil amendment. Like most charcoal, biochar is created by pyrolysis of biomass. Biochar is under investigation as an approach to carbon sequestration to produce negative carbon dioxide emissions. Biochar thus has the potential to help mitigate climate change, via carbon sequestration. Independently, biochar can increase soil fertility of acidic soils (low pH soils), increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Furthermore, biochar reduces pressure on forests. Biochar is a stable solid, rich in carbon and can endure in soil for thousands of years.

As environmentally diligent growers are quick to note, biochar has been used to enhance soil fertility and texture for thousands of years. It has been revealed as the secret ingredient of the perennially fertile terra preta soils of the Amazon Basin, which formed islands of agricultural productivity in an area otherwise noted for its impoverished soils, almost useless for long-term farming. These anthropogenic soils are discussed in detail in Charles Mann’s best-selling book, 1491: New Revelations of the Americas Before Columbus, a work well known among these growers. Interestingly, much of Mann’s analysis is rooted in the scholarship of geographers such as William Devevan who had trained in the old Berkeley school of cultural geography, the source of my own graduate education.

Growers who use biochar in hope of neutralizing their carbon budgets are also concerned about soil fertility. Charcoal by itself does not enhance fertility to a significant degree and can even be harmful if used in raw form, but it does allow fertility maintenance by greatly reducing nutrient leaching; it also boosts soil porosity and water retention. Biochar enthusiasts claim to be making investments that will last for thousands of years, permanently improving the quality of their lands. Growers who use biochar also argue that it produces healthier plants than those grown under other conditions. They have not, however, carried out any controlled experiments.

The growers I interviewed produce biochar in a crude manner. They simply burn piles of firewood during the rainy season, and then shovel dirt on the glowing embers after the flames have died down. The resulting charcoal, along with the potassium-rich ash, is then thrown into large hand-dug holes, approximately four feet deep and ten feet across, where it is mixed with manure, compost, and native soil and then allowed to age for months before planting. The growers admit, however, that this process is far from ideal, as it is both wasteful and polluting, generating a great deal of smoke. Much preferable, they contend, would be wood pyrolysis, which would allow them to capture both the flammable gasses and the smoke particles, turning them into useful products. The video pasted in below, produced at Appalachian State University in Boone, North Carolina, shows what they regard as an ideal system, one that would produce not only biochar but also wood-gas for home, water, or greenhouse heating, as well as wood tar (creosote); how exactly the wood tar would be used remains unclear**. But despite the enthusiasm of a few growers, no one has yet constructed a pyrolysis apparatus. One problem is that dreams here tend to exceed realities. Whether that results from excess consumption of the crop produced on these micro-farms remains an open question.

 

 

Finally, the enthusiasm for biochar extends beyond carbon sequestration and soil improvement to encompass landscape management. A significant amount of wood must be cut every year, they insist, to preserve the existing ecological balance. The area in question supports a vegetational mosaic in which dense redwood and tanoak forests predominate on north- and east-facing slopes, but where south- and west-facing slopes are, or at least were, mostly covered by grass. Rainfall is heavy enough, however, that forests spread everywhere in the absence of human intervention. In earlier times, regular burning maintained the mosaic. Native Americans burned extensively, and the sheep-raising settlers who replaced them intensified the practice. But with fires all but eliminated, grassy slopes are being colonized vigorously by Douglas fir and a few other light-loving tree species. As a result, open-country animals such as jackrabbits (hares, actually) that were formerly abundant have been diminishing in number. Biochar production, its proponents argue, thus helps maintain a higher level of biodiversity than would otherwise be found.

One grower goes so far as to contend that biochar offers a global solution to almost all problems associated with climate change, energy production, and agricultural productivity. Here my deeply cultivated skepticism kicks in. At the local scale, biochar does seem to offer a number of advantages, but in planetary terms I suspect that its promise is quite limited. But I would certainly like to see more research on the topic.

* As mentioned in the first post in this series, the growers in question all run small-scale operations that are as legal as possible. They cultivate under medical license, remain within the county’s 25-plant limit, and sell their product to official medical dispensaries. According to the federal government of the United States, however, their activities are completely illegal.

**Wood tar does have a wide array of potential uses, the most intriguing of which are medicinal and gustatory. Food preserved by smoking is essentially conserved by tar. According to the Wikipedia,

In Finland, wood tar was once considered a panacea reputed to heal “even those cut in twain through their midriff”. A Finnish proverb states that “if sauna, vodka and tar won’t help, the disease is fatal.” Wood tar is used in traditional Finnish medicine because of its microbicidal properties.

 

Wood tar is also available diluted as tar water, which has numerous uses:

• As a flavoring for candies (e.g., Terva Leijona) and alcohol (Terva Viina)

• As a spice for food, like meat

• As a scent for saunas. Tar water is mixed into water, which is turned into steam in the sauna

• As an anti-dandruff agent in shampoo

• As a component of cosmetics.