Selecting Species for Coppice Firewood
With all the snowstorms blanketing much of the US right now, I feel a bit guilty that I’m still visiting family in Florida, where I grew up and where it is a cool 72ºF/22ºC outside. On top of that I’m hearing that in the Southwest, natural gas shortages are leaving many homes without heat. (One Twitterer complains that President Obama caused the shortage by blocking drilling for natural gas and oil; I think this person misses the point that the shortage is caused by the unaccustomed cold weather shutting down refining and distribution facilities.)
We can’t rely on fossil fuels for long—natural gas peak production may be a few years further off than the crude oil peak, which by all reasonable accounts is either here or imminent. With all the attention the generation of electricity gets in the media—and there’s no denying solar photovoltaic, solar thermal, and wind turbine electricity sells pageviews—one of the most crucial problems we will have to face in our transition off fossil fuels is heating our homes.
It is becoming more and more apparent to everyone with the sense and knowledge to see it that global warming climate change weirding doesn’t mean six fewer months of winter. It means more severe weather all around—worse storms, worse droughts, worse snows, and worse summers. So planning for heating our homes is still going to be a major challenge. We need solutions that will keep us as warm as we need to be, without making the pollution and climate change problems worse. And surprisingly I think a big part of that is going to be firewood.
But we’ll need to manage our firewood in ways that don’t just sustain the status quo but actually help regenerate the land we’re part of. And a big part of this, I believe, is going to be establishing coppice systems.
Coppice is the practice of cutting trees so that they resprout from the stumps. Famously, Europeans and Native Americans have practiced coppice silviculture for firewood, basketry, and building materials. Willow is an especially favored species for basketry and certain types of building—the wattle and daub houses of ancient Britain come to mind. But willow makes lousy firewood. So what species coppice well and make good firewood?
Alder, ash, and black locust are all good coppice trees, resprouting easily from stumps and growing quickly. Ash is very good firewood. Reports differ on alder and black locust, and I suspect the efficiency of one’s stove will have a lot to do with how completely these woods combust (on which more later). One species I’d like to highlight, especially for people in the southwestern US right now, is Parkinsonia aculeata, also known as horsebean, jerusalem thorn, and blue palo verde, among other common names.
What’s good about this tree? Well, for one thing, it’s drought tolerant. The effects of global climate change on local rainfall patterns is not yet known, but it’s possible that areas that already get very little rainfall will get even less, and some areas with moderate rainfall will become drier while others will become much wetter. For the desert southwest and arid parts of California, Parkinsonia aculeata could be very useful. It is partly cold hardy, tolerating temperatures down to 18ºF/-7ºC. It is also leguminous, with the potential to restore nitrogen to the soil, although I believe this has not been studied in this particular plant. And when cut it regrows from the stump. It is also good bee forage, attracting pollinators with its bright yellow flowers. Its main drawback is that it can be invasive—because it propagates readily from seed or from cuttings, it’s hard to control. Arid environments help to control its reproduction from seed; it shouldn’t be planted in areas where there is more water than it needs. And here’s where another benefit of this plant comes in handy—it makes excellent goat browse. Livestock eat its leaves and seed-containing pods, and the fresh pods have a sweet edible pulp.
How might you manage this plant, given its tendency to become invasive in areas where it gets more water than it needs?
Well, first, I’d avoid planting Parkinsonia aculeata in moist meadows, streambanks, or near ponds or irrigation. Dry upland slopes are a better place. Second, cut it back on a regular basis for wood, and don’t plant more than you can use. Don’t leave fresh cuttings lying around on top of fertile soil. Finally, graze goats through the planting on a rotating basis so they can browse back new growth and seedlings and eat some of the edible seed pods. Pigs might also enjoy the pods and would probably disturb the ground under established trees to discourage new seedlings, but be careful they don’t rip up the roots of the established trees you’re coppicing.
It’s also important to get back to wood stoves that can efficiently and cleanly burn small-diameter firewood. If we aggravate our air pollution woes with particulates from incomplete burning, we’ll make our situation much worse. If we exacerbate the problem of carbon release by burning up existing trees and releasing their carbon without planting enough new trees to store the carbon we’re releasing and then some, we’ll make our situation much worse.
We’re running out of the carbon trust fund we’ve inherited in the form of fossil fuels, and we need a wise plan to help us live within our ecological means.