"If you appreciate the effort it takes for a single individual to become carbon-neutral, you can appreciate what it might take to balance the carbon footprint of a modern city of tens of millions of individuals."
In 1979, with the birth of my second child, my mother followed me to Tennessee and bought 88 acres near our budding ecovillage. Since our intentional community used to sharecrop that land, the fields had been contour terraced and swaled in the late 1970s with The Farm’s bulldozer and road grader, using guidance from the local soil conservation service (another Roosevelt relic), so it was already in pretty good condition from a keyline management point of view. I took the local USDA extension agent’s suggestion and planted loblolly pine (Pinus taeda), which, it turns out, was good advice. The loblolly is hardy, fast growing, drought-tolerant, and its range is expanding as the Southeast warms. I also planted hybrid American chestnut, mulberry, hardy citrus and bamboo.
|The length of the frost-free season (and the corresponding growing season) has been increasing nationally since the 1980s. NOAA/NCDC, National Climate Assessment 2013 (advance draft).|
In 1977-78, even before my mother purchased her farm, I began experimenting at my home with fast-growing hybrids of poplar, developed in Pennsylvania, comparing their growth characteristics with native tulip poplar (Liriodendron tulipifera). I was looking for a sustainable winter heating supply and a substrate for mushroom production that could be harvested by coppice and pollard. In 1985 I applied that knowledge to plant a shelterbreak of hybrid poplar along one border of my mother’s property.
Walnut Hill Farm
|Interior of the Prancing Poet, under construction in 2012|
In 1998, I planted out 3000 hybrid walnuts, comparing grafted rootstock developed by Purdue University for veneer with native black walnut used primarily for furniture and hardwood flooring and secondarily for a prodigious, oily nut crop. Nearly all of the expensive hybrid plantings were lost within 5 years to rabbits, insects, drought, and ice-storms. The native walnuts succeeded, and so have become a lasting part of my forest design at what our family now calls Walnut Hill Farm. We are using the oily husks this winter to stain the interior trim in a new addition to The Farm’s Ecovillage Training Center.
The late 1990s also saw the introduction of many bamboo stands, along the swales and in “canebreaks” where creeks would overflow in high water. I put in a half-dozen varieties in discrete patches, spread over about 20 acres. These have multiplied so quickly that they alone more than offset all the annual carbon consumption at Global Village Institute, including the Ecovillage Training Center and all its employees, visitors and volunteers, and all my annual travel around the world giving courses and workshops. Counting sequestration both above and below ground, 10 acres of bamboo locks up 63.5 tC/yr (metric tons carbon per year).
I am told by Peter Bane, author of The Permaculture Handbook, that six tC/yr is consistent with back-of-the envelope figures for maize, another C-4 photosynthesizer. The difference with bamboo is that being an annual, edible corn is harvested and consumed each year and the stover decomposes rather quickly, releasing briefly stored carbon as greenhouse gases. Maize is therefore actually a greenhouse pump, because it draws soil carbon into the thick-rooted plant and makes it more readily available to the atmosphere. Bamboo, if it is landscaped into groves or incorporated into furniture, buildings or biochar, lingers much longer in the terrestrial environment.
The Albert Bates Forest (we do not call it that; I am being facetious) now occupies some 30 acres. After my mother died, the Institute leased 44 acres from Walnut Hill for the project and planted fruit trees, berry bushes, bamboos and cactus, as well as the tried-and-true local trees. We know that climate change will cause many of our most familiar tree species to out-migrate, and we are working to fill the void by planting species more likely to survive in semi-tropical conditions, albeit punctuated by winter blizzards.
Planting trees is not as easy as it seems when your experience is mainly hardy transplants of Loblolly pine provided by the Forest Service in tight little bundles. Most trees resist being transplanted and have to be encouraged and pampered. Oliver Rackham, in Trees and Woodlands in the British Landscape (2001) says “planting a tree is akin to shooting a man in the stomach.” His point is that trees are uniquely adapted to the angle of the sun, the flow of subsurface water and nutrients, the community of the forest and other factors we seldom consider. Starting trees in situ from seed or small seedling is often more likely to succeed than transplanting them as grafted rootstock or even semi-mature trees.
My planting method relies heavily on natural regeneration, followed by selection for desirable traits. Because of the poor highland soil in our region, cedars are a common pioneer species. Tulip poplar and black locust (Robinia pseudoacacia) are also common. Most disturbed ecosystems will revert to woodland through natural succession if left un-grazed and un-mowed. We have mowed those areas we wanted to reserve for planting stands of higher value. Self-sown trees are generally stronger and grow faster than planted trees, so by allowing space between patches, we left plenty of room for natural succession through self-seeding.
Most tree work is done in our dormant season, roughly from mid-November to the end of April. My son now has a nursery established at Walnut Hill where he starts seeds in containers in polytunnels in the summer months, transplanting seedlings out in winter. He is good at scavenging plant leftovers from nursery sales and farmers markets, and although those trees have diminished survival rates from excessive handling and neglect, some always manage to survive and mature. From these, new generations are cultivated and encouraged.
I have been planting at densities of about 100 trees per acre, but those densities will increase substantially as the forest fills itself in. I imagine 400-1000 trees per acre to be more typical at climax, plus a wide range of understory plants. I asked Frank Michael, Global Village Institute’s engineer, to run these numbers for me. He used several approaches to cancel out the various unknowables. This is part of a work in progress that he plans to publish as a book in the near future.
Calculating Carbon Sequestration
For a mature mixed-oak-hickory mesophytic forest of the type we are planting in the Highland Rim region of south central Tennessee, hard data is not readily available, but the appendices to the First State of the Carbon Cycle Report of the US Climate Change Science Program (2007) are very helpful. Studies aggregated by the National Oceanic and Atmospheric Administration suggest that 400 trees (one acre at maturity) would structurally absorb 2.6 tons of carbon per year (2.6 tC/ac-y or 5.84 tC/ha-yr,), based on studies at 6 sites over 34 years. Our 30 acres are now at about 5% of the eventual biomass density, so they are sequestering 3.9 tC/yr. At maturity they would sequester 78 tC/yr. Foresting the full 44 acres would sequester 114.4 tC/y.
Another approach is to use a coefficient for average forest sequestration. A standard reference for this work is Akihiko Ito and Takehisa Oikawa’s “Global Mapping of Terrestrial Primary Productivity and Light-Use Efficiency with a Process-Based Model,” in Global Environmental Change in the Ocean and on Land, M. Shiyomi et al., Terrapub, Eds. (2004), pp. 343–358. If we apply the number Ito and Oikawa cite — 0.5-0.6 kgC/m2-yr for second growth Northern woodland — to our 44 acres (178,000 m2), we arrive at 89-107 tC/yr at maturity, which is in the same ballpark as estimating structural mass using NOAA’s figures. Since we are only at 5% maturity on 30 acres, the forest is presently saving about 3 tC/yr.
Using the carbon calculator on the Dopplr web site, and tracking my average annual travel for the past five years, I produce about 10 metric tons/yr of CO2, or 2.72 tC, from my jet-setting lifestyle. In order to also include all the embodied energy amortized into my food, clothing, gadgets, workplace and home, let’s call it 5 tC/yr, although that is likely an over-estimate. So, at this point in time my tree plantings are not covering my footprints, although my bamboo plantings are, and I am also neglecting to mention my experiments with algae in constructed wetlands. Algae and bamboo are the number one and number two fastest photosynthesizing plants we know of.
The estimate of potential average annual sequestration by my forest at maturity, even without bamboo or algae, is 89-114 tC/yr at a stocking density of 400 trees/acre, in perpetuity. That will erase my footprints with the soils of time.
By 2050 this forest should be relatively mature, and so would only continue to stock carbon at the same rapid rates it did as a juvenile forest if it were to be selectively harvested. In The Biochar Solution I described the method proposed by Frank Michael for step-harvest. I presume that most of the wood harvested at that point would be used in buildings or for biochar, further sequestering its carbon rather than oxidizing it back to the atmosphere through decomposition or burning.
In the step-harvest method, mixed locally-native species are planted in a tight grid spaced to reach closed canopy in 4-6 years, at which point half the young trees are harvested and used for biochar manufacture (and accompany heat capture); the biochar is returned to the patch. In nine years, the remaining trees again close canopy, and half are harvested for biochar and lumber. This cycle is repeated at 12, 16.5, and 24 years, etc. At each point, there are several options:
1. Harvest all the trees and start a whole new planting cycle;
2. Insert a farming/gardening rotation in the open areas, adding mulch, compost teas, biochar and compost as soil amendments; or
3. Allow remaining trees to mature and re-enclose the canopy, while allowing or adding useful understory plants.
The first option yields greater than 6.2 times the biomass per unit of time and area than a conventional commercial forestry plantation.
“I tried to discover, in the rumor of forests and waves, words that other men could not hear, and I pricked up my ears to listen to the revelation of their harmony.” — Gustave Flaubert, November
My hope is that long after I am gone, my life’s forest will continue to provide valuable ecological services of all types to those who inhabit it after me, whether that is for climate mitigation or for the sense of wonder that growing up among tall trees can give to a child.
I recognize that it is an extraordinary luxury for one human to have access to 40 acres of land and be able to devote the resources required to establish a lasting, productive and climate-resilient forest. I don’t wish to suggest that everyone could or should do this — just multiply 40 acres by 7.2 billion people and you see how impossible that would be.
What I am saying is that the carbon footprint of millions of people who live at the standard of living I do, racking up air-, sea- and ground-miles and using server farms powered by fossil energy slaves to book our next business trip, will not just go away by itself. Earth’s carbon cycle is profoundly out of balance (as are the nitrogen, potassium and other cycles) — so much so that those conditions now threaten our extinction.
If you appreciate the effort it takes for a single individual to become carbon-neutral, you can appreciate what it might take to balance the carbon footprint of a modern city of tens of millions of individuals. Reports that city dwellers are more ecological than their country cousins often overlook this kind of calculus.
So what is the prescription? While not everyone can plant a personal forest, everyone can estimate their own greenhouse footprint and begin reducing it. I have been giving seminars in how to heat your home with stoves that make biochar, and how to use biochar in your garden to grow more biomass, including winter fuel. I am also active in the ecovillage and transition towns movements, which are pioneering a brighter, happier, cooler future. Planting trees helps. More forests are better. That just may not be enough.
This is the second of a two-part piece. The first part was published to The Great Change on January 22, 2013.