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To burn or not to burn: Is that even a question?



For the Gazette
Friday, July 27, 2018

For many years my wife and I have stayed warm by burning locally harvested firewood in a high-efficiency, EPA-certified airtight woodstove. Adding insulation, replacing leaky windows with low-E thermopane units, putting this stove into our inefficient fireplace — all are simple and cost-effective measures. We take pleasure and some pride in the annual rhythm and exercise of stacking and moving the wood. And we look forward to fall and winter when we gather around the warm presence of the stove, immune to power outages, independent from fossil fuel, reducing our carbon footprint.

But a while back, new research concluded that biomass energy was not as carbon neutral as we had thought. Perhaps wood burning was even worse than coal! Ouch!! Were we making a mistake?

We knew our wood heat is not fully free of fossil fuel inputs — the trees are felled, bucked and split with gas-powered chainsaws, delivered in a gas-powered vehicle. But, managed correctly, trees are definitely a renewable resource. In the Pioneer Valley, we essentially live in a forest. Only natural disasters and such activities as growing lawns, pruning, farming and paving stop and reset the natural process of succession. The carbon released as we heat our house certainly could return to long-term storage in biomass and soils, while that released from fossil fuels is never going back.

Yet technology has moved ahead since we purchased our stove 20 years ago. Solar and wind power sources are economically feasible and growing rapidly. Building design and construction has matured and energy requirements for space heating can be greatly reduced. And solar-powered air-sourced heat pumps have entered the market as viable, reliable alternatives to combustion for heat. Perhaps a re-think is in order?

Is the widespread use of woody biomass for fuel sustainable? Of the roughly 3 million forest acres in Massachusetts, about 1.75 million acres are available for active harvesting (the rest is parkland, reserves, too steep, etc.) and have species desirable for fuel, mainly hardwoods. There are at least 50 million cords in live trees on this land, growing at a rate of a million cords of wood each year.

So, there could be sustainable production of 1 million cords on 1.75 million acres, an average of about 0.6 cords per acre per year. The current yearly extraction rate of wood from Massachusetts forests, given varying soils and terrains, averages out to 0.13 cords per acre. Clearly, wood is still accumulating at a rate of anywhere from 0.2 to 0.6 cords per acre, even with active harvesting.

What about demand? A conservative harvest of ⅓ cord per acre per year, fueling a 2-cord-per-home demand, needs 6 acres per home. Our current forests could provide a sustainable supply to 300,000 homes — just about the total number of households in Franklin, Berkshire, Hampden and Hampshire counties. Well-managed woodlots could produce more than 1 cord per acre, heating as many as 1 million homes.

Should we do this? What about ecological impacts and carbon neutrality? We must consider that a managed forest, while responsive to human needs, and with its own aesthetic appeal, is not a fully functioning wild forest. We might well decide that much more forest than the current 1.25 million acres should be left out of management. We do, however, depend on wood for construction and other purposes. We can either meet at least some of those needs locally or import all of our forest products from other states and countries. Local, sustainable production is desirable, and certainly possible.

How about the impact on the global climate cycle? Think of our forests as a carbon savings account. Removing renewable wood for fuel is like taking a sustainable draw on that account. As long as the draw does not exceed growth, then the principal remains in play, removing carbon.

Here’s the challenge: In the northern hemisphere, there’s an annual cyclical dip and rise in the atmospheric carbon dioxide (CO2) level. In warm weather, plants take up CO2 and make an excess of sugars and wood, adding to the carbon savings account. In winter, respiration by stems, roots and decaying organic matter exceeds uptake and the concentration of CO2 temporarily increases. Unfortunately, the rise of CO2 continues upward past 400 ppm as we burn fossil fuels and continue deforestation — we are seriously overdrawing the account. Can we, through sustainable management, make up the deficit caused by burning cordwood? How big an impact will there be from removing a small but sustainable fraction of a forest’s carbon, on an annual basis?

Burning a cord of hardwood releases 2.5 tons of CO2, so a 600,000-cord annual harvest and regrowth in Massachusetts represents about 1.5 million tons of CO2 cycling in and out of our forests each year. How much would this add to global CO2 ? At 400 ppm the total estimated CO2 in the atmosphere is 2 million million tons. So annual wood harvest and burning in Massachusetts would create a maximum temporary increase of 0.0003 ppm. (For the math, see * below.) This means that, if cordwood is managed sustainably, then wood burning in our stoves, though not strictly carbon-neutral, is climate-neutral.

This analysis applies only to locally produced and burned cordwood. Imported wood pellets and large-scale biomass cogeneration present a very different picture.

So, I’ll keep my wood stove for now, supporting a local land-based sustainable economic activity, reducing dependence on fossil fuel and getting some exercise in the bargain.

* The calculation on the effect of burning cordwood in Massachusetts is as follows:

Step 1: (1.5 million tons CO2 added to atmosphere)/(2 million million tons CO2 in atmosphere) = 0.000075% increase.

Step 2: 0.000075% increase x 400ppm = 0.0003ppm increase. The increase is temporary if regrowth in the forests equals the amount harvested.

Lawrence J. Winship is emeritus Professor of Botany at Hampshire College.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 845 West St, Amherst, appears every other week. For more information go to www.hitchcockcenter.org, call 256-6006 or write to column@hitchcockcenter.org.