Is mass timber construction really renewable and sustainable?

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A new study says it is, and we speak to one of the authors.

There are a number of questions that come up every time we talk about mass timber construction, which I was hoping might be addressed in the new guide to North American Mass Timber- State of the Industry 2019. The guide is produced by the Forest Business Network and acknowledges support from almost every big name in the mass timber industry, so we cannot call it an unbiased source, but they do address those hard questions, right at the start of Chapter 2: Forest Resource, written by Dave Atkins.

  • Will North American forests be decimated by the increased demand?
  • How will wildlife habitat and watersheds be protected as timber harvests increase?
  • If deforestation is a concern, why even consider a new use of wood in construction?

They start by noting that there is a lot of forest in the USA, 766 million acres, and the majority of it is owned privately. Ninety percent of timber harvested for lumber comes from private, corporate lands.

“So that means about 90 percent of the timber harvested in the United States comes from about one-third of the timberland base. The remaining two-thirds of U.S. forestlands are mostly managed for other purposes, while producing a small but important amount of timber for the marketplace.”

In Canada, the opposite is true; almost all the land is “crown land,” close to a billion acres of forest. Most forest lands in North America are now certified under standards like FSC, SFI (a major TreeHugger sponsor), CSA, and ATFS, so there are some controls on how wood is harvested almost everywhere.

The big question: Is there enough of it? The important datum is the growth to drain ratio: Is more being harvested or lost to bugs and fire than is being grown?

Forest growth© Mass Timber: Industry Report

“Since the 1970s, the ratio has been greater than 1. This means that each year, the United States is growing more timber than it loses to timber harvest and natural mortality. These findings show that increased demand for lumber and other forest products arising from the development of mass timber can be met without over-harvesting forests in the United States.”

And that only accounts for 64 percent of the forest land in the USA. The graph also shows that the harvest is actually down while the mortality is going up thanks to fires and disease. Much of that diseased wood could be used if there was more milling capacity, so much of which was shut down when wood fell out of favour. If there were more demand for wood, it might help actually help the forests, dropping the mortality and increasing the harvested wood.

So, back to our three questions:

Will North American forests be decimated by the increased demand? The data show that forests in Canada and the United States are growing far more wood than is being harvested. An increased demand for timber will not lead to deforestation.”

“How will wildlife habitat and watersheds be protected as timber harvests increase? Extensive forestlands reserved from timber harvest provide wildlife habitat and preserve watersheds. Timberlands managed for production also provide a number of these values.”

“If deforestation is a problem, why even consider a new use of wood in construction? In North America, the quantity of forestland has been stable for decades. The use of wood products provides an economic incentive to protect those forests from conversion to non-forested uses.”

forest wood cycleUS Forest Service/Public Domain

Later in the guide, the authors address the question of carbon: does wood truly sequester all this CO2, and is it better to chop than to leave the forest to its natural cycles? In the USA alone, forests are storing 10 billion metric tons of carbon. Without human intervention, a tree is carbon neutral; it absorbs carbon for growth, then, when mature, it maintains its current systems and is not as efficient at storing. Eventually it declines and dies, releasing all of its carbon back into the atmosphere.

When trees are chopped down and turned into mass timber, it doesn’t return that carbon to the atmosphere for decades; it’s stored in the buildings.

The authors also point out that in developing countries, the land is more valuable for agriculture than the trees are, causing deforestation. In Europe, wood has become really valuable and there is reforestation and afforestation happening, forests expanding everywhere because it makes a high-value crop.

We have noted recently on TreeHugger that there are significant upfront carbon emissions from making building materials like concrete or steel. The authors conclude:

“When wood is chosen over steel or concrete building materials, the net effect is a reduction in fossil fuel use. The benefit is immediately achieved when a building is constructed, and it significantly slows the increase of atmospheric carbon dioxide. Mass timber, in combination with a variety of other wood products, can replace many products currently derived from sources that are more heavily dependent upon fossil sources. Forest products can be the foundation for a more sustainable, low-carbon society.”

Lumber truck on Haida GwaiiLumber truck on Haida Gwaii/ Lloyd Alter/CC BY 2.0

There are some who complain that wood isn’t quite so wonderful and efficient as I have written, or that the Mass Timber Manual suggests. They claim that the equipment uses a lot of fuel, that a lot of the wood and “slash” is left in the forest to rot, and, at the same time, that soil is not being rejuvenated if the wood is removed. We noted in an earlier article that there are some who are skeptical about how much carbon is actually sequestered in wood construction.

About fifty percent of the tree makes it into mass timber.

Mass timber in TorontoNail-laminated Timber on Glulam Beams and Columns in Toronto/ Lloyd Alter/CC BY 2.0

I called Dave Atkins, the author of the section, to discuss this and he told me that the consensus in the research is that 50 percent of the carbon in the form of wood makes it to the mass timber. Some wood is left on in the forest specifically to rot and provide animal habitat; some scraps are burned to kiln-dry the wood.

But if the trees were left in the forest, fully 100 percent would eventually be released into the air, so 50 percent is pretty good. Atkins also notes that “if you don’t grow it, you mine it.” And all that concrete and steel is made with fossil fuels.

There are also some who note that mass timber uses up far more wood than other types of wood construction, and they have a point; in low rise buildings, advanced robotic wood framing can deliver a great product for less money and a lot less wood.

Some have justified the use of Mass Timber by saying “If we use more wood, we are then growing more trees and absorbing more CO2,” but if the real utilization is 50 percent, then it is producing a lot of CO2 now, even if it is from renewable sources, the atmosphere doesn’t notice the difference. So we should be using it as efficiently as possible. Or as was summarized in a tweet:

But when you read all the pros and the cons, and even if wood and the industry are not quite perfect, there is simply no comparison in the upfront carbon emissions of the manufacture of mass timber compared to other materials; and that for the life of the material (which can be a very long time), it is storing carbon, about a ton of carbon for every cubic meter of wood. Dave Atkins says wood is renewable, biodegradable and sustainable. It is hard to argue with that.

A new study says it is, and we speak to one of the authors.



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