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  • Writer's pictureEdie Sonne Hall

Thoughts on the Longer Rotation Climate Solution for Washington State- Is it a Sure Bet?

Updated: Mar 24, 2022

I am constantly asked about whether it is better to let a tree grow or to use wood products. There is a perception that this is an either/or, but it is not. You can grow more trees and use more wood products. However, as with anything, the devil is in the details. Forests are complex and so is climate change. This post attempts to lay out some considerations to a question that is of particular importance to Washington State regarding the best strategy to help meet a net zero GHG target for our state’s greatest asset- our evergreen trees.

The Context- Meeting the needs of a Growing Population and Net Zero

Reaching a net zero GHG target by 2050, which is what the IPCC urges is needed to prevent catastrophic climate changes, requires a fundamental re-examination of not only where our energy comes from but also how materials are made. Already, 23% of total global emissions or 11Gt CO2e come from the process of extracting resources to make and move “stuff” - from housing to transportation to food[1]. The quantity of natural resources extracted annually increased twelvefold between 1900 and 2015 and is expected to double again by 2050 (International Resource Panel 2020).

Currently, 74 percent of the resources we use are non-renewable (IRP 2020). However, much of societies needs can be met with renewable alternatives, which can be grown and manufactured with less embodied carbon emissions. Renewable forest resources can play an essential role in providing low carbon and even negative carbon products and energy. At the same time forests both sequester and emit carbon dioxide. Given that our goal is to reduce atmospheric greenhouse gases our focus should be designing a global system that 1) puts less GHGs into the atmosphere and 2) takes more GHGs (in particular) carbon dioxide out of the atmosphere.

Washington State’s Competitive Advantage

What does this have to do with Washington State and the rotation age of Douglas fir? Well, quite a bit. Washington is a great place to grow trees - with productive soils and a relatively long growing season. Washington State has the highest percentage of lands in high site productivity indices, perfect for conifers like Douglas-fir, which is widely touted as a quality building material. Washington also has some of the most stringent forest regulations in the world. As a state, Washington is the 2nd largest producer of sawtimber in the US, which, as a country, is a global leader in sawtimber production. Washington’s contribution to meeting global timber demand is significant, and the growth and production of this important renewable resource is one of Washington’s best competitive advantages.

Missing Considerations

Recently, there has been a lot of talk about the importance of Washington’s forests from a carbon sequestration perspective. Some “proforestation” efforts are calling for dedicating forestland completely for carbon sequestration, by stopping or severely reducing harvesting (Graves et al 2020, Moomaw et al 2019). These generally miss the boat - there is no recognition of the climate benefits associated with using wood products compared with other materials and no thought to leakage to other forests or other materials (NCASI 2020). Others are calling on lengthening rotations, while still allowing for harvest, as the only way to increase carbon storage in forests. In certain situations, lengthening rotations can result in more yield per acre over the long-term. However, when longer rotations are touted as the sole solution to forest climate mitigation, we’re missing some critical considerations.

It’s time for us to pause and unpack the specifics about longer rotation age and carbon sequestration in the context of the global challenge of climate change and the more local considerations of Washington State.

1. Biological Culmination of Mean Annual Increment (CMAI) vs Financial Optimal Rotation- It is widely accepted that the theoretic biological culmination of mean annual increment delivers the most volume and carbon sequestration over time. Biological CMAI is calculated by the inflection point of volume divided by stand age. This biological “sweet spot” can differ from the financial optimal rotation age because although physically a stand may still be growing more every year, the landowner also has money invested in said stand. As the saying goes “time is money”. So much money that the difference in NPV between a 45-year rotation (which is the economic optimal rotation age at a 5% discount rate) and a 65-year rotation has been identified as a financial barrier that carbon prices on the order of $50 per ton of CO2e would need to bridge the gap (Diaz 2018)- and more when timber prices are higher.

2. Variation in Biological CMAI- Leaving money aside for now, what is often overlooked is the variability of the optimal biological rotation for particular species, site indices, and management regimes. CMAI rotation age varies tremendously by species, from 25 years in managed loblolly pine in the southern United States to 125 years for mountain hemlock in the Rocky Mountains (Smith et al 2006). CMAI also varies by management intensity and site index within a species. For example, non-managed Douglas-fir forests have an average CMAI of about ~95 years, while intensively managed forests, with silvicultural practices such as thinning and improved planting, the CMAI reduces to approximately 55 years (Smith et al 2006). Why? These practices have been found to improve productivity in Douglas fir forests by up to 43 percent (Vance et al 2010). So, the “magical age” of 80 years or 90 years for Douglas fir forests, as suggested in various articles (Law et al 2018, Swedeen op ed 2021) is too long for intensively managed forests- in other words, you will be producing LESS harvest in the long run if you keep an intensively managed Douglas fir forest past the age of 55-60 years old. Again, this is if the goal is to produce the most efficient carbon and wood product strategy focusing on the land only. It’s important to take into consideration the site index, management, species, and geography when looking at the carbon potential in forests.

3. Implications for a Transition- Currently not all forests are managed, nor are the forest landowners or managers compensated to manage, for their respective and variable CMAI rotation age. Some forests are harvest in shorter timeframes, some in longer, and some not at all. The first question is: do we want all forests to be managed at their CMAI? I’m guessing those of us that value forests for way more than carbon would definitively balk at prioritizing carbon alone above biodiversity, recreation, water, fiber supply, and more. But since this blog is purely focused on climate, let’s concede that if we could wave a “magical wand” where Washington’s working forests were already managed (and compensated) to manage for their respective CMAI, this could result in more harvested volume and more carbon in the forest. This, in turn, would definitely help reduce atmospheric GHG emissions as fiber supply and carbon in forests could increase. In absence of a “magical wand”, what would be the implications be of the transition?

There are two important barriers that would need to be addressed in order to result in reduced atmospheric GHGs: 1) mill diameter size limits 2) Filling the gap of fiber supply (e.g., temporarily replacing harvest from stands that are in the “lengthening rotation stage” with stands already above CMAI). Let’s tackle each of these separately.

Large Mills- At a certain point, trees grow too large for current mill capacity, which are generally set up to accept logs less than 30-36” in diameter. Already 16 percent of the volume of Douglas fir in Washington State is in trees larger than 35” in diameter (Oswalt 2017, Table 35). We need to be aware of practicalities and work with mills to understand their desired fiber material. Put bluntly, if we grow trees longer (and bigger) do we have the capacity to mill these larger logs? If the answer is no, then we need to build this capacity first.

Reduction in Harvest- Let’s assume the mills in our Washington are configured to process logs from trees grown to the region and species-specific CMAI. What happens if we start paying forest landowners to “delay their harvest”? For context, there is already technology in use that can find stands at the economic optimal rotation age and even a platform that can pay those landowners to delay harvest on a short-term basis. Will this help reduce atmospheric GHGs? To answer this question, let’s look at this from the mill’s perspective. A mill sources their fiber from a wood basket, which includes multiple landowners and forests. If a subset of acres in that wood basket that would have supplied their mill that year but instead are getting paid to hold carbon on the stump a little longer, what happens to that mill? Does it source from another location? If so, what is the age of that different stand and where is it located? Are there more or less emissions involved in transportation of the logs? In carbon offset projects this is known as leakage, and there is a deduction taken from the quantified carbon credits to account for this. But what if the scale of uptake in “delayed harvest” carbon schemes is so large that there is in fact a reduction in landscape level harvest (which is the assumption that was used in the Robertson et al 2021 study and based off the Fargione et al 2018 methodology)? Will this result in a decrease in atmospheric carbon?

I argue, that unless done right, it will not. If not done right, there are two possible outcomes of a wide-scale transition period, which could last more than thirty years of harvest reduction in Washington. The first outcome is that harvest increases in other countries. Considering that Washington has some of strictest forest practices and protection measures in place and grows one of the best trees used for building materials, that would be a very “un-environmental” thing for us good Washingtonians to do. The second outcome is that global wood product production is reduced and, without a reduction in material consumption, the result is using more energy-intensive materials. From a climate perspective, this outcome is even worse! Almost 40 percent of annual GHG emissions are attributed to the building and construction sector, and a quarter of these emissions are attributed to embodied carbon (emissions associated with manufacturing the material used in construction) (UNEP 2020). Cement alone accounts for 8% of global GHG emissions, and under business-as-usual projections, is expected to increased production from 4.2 billion metric tons in 2016 to over 5 billion tons/yr. by 2050 (IEA 2018).

The Solution- the Biological CMAI without Reducing Harvest

Neither of these outcomes serve to benefit the global challenge we are facing nor provide solutions. How could it be done right? Harness the stands that are older than CMAI and bring their volume into the wood fiber supply while other stands grow. Ironically, the same platforms that can find the 40-year-old stands can also find the 80- to 90-year-old stands. According to Washington State’s recent state inventory report analysis, there are 500,000 more acres in the 81-to-100-year age class now than in 2006. While some of the forests will keep growing for a long time, others are overstocked and at risk for mortality from disease or fire.

We just need to make sure we have the milling capacity for these larger logs and the political and social support to harvest these older stands.

Forest Products + Carbon Stocks = Winning Solution

To meet the needs of our growing population, we absolutely must embrace a renewable resource economy. Our goal should be to increase production of forest products in concert with increasing carbon stocks. This is achievable. A recent FAO report recommends the following policy guidelines for national or sub-national regions (Verkerk et al 2021):

· Incentivize and encourage responsible production and consumption of sustainable biobased products and discourage the use of non-renewable, fossil-based and GHG-intensive products.

· Consider the important role of forests and forest products in a functioning, circular bioeconomy, including carbon storage by forest ecosystems, carbon storage in wood products, product substitution effects and possible leakage effects.

· Exclude actions that favor climate change mitigation locally but lead to deforestation or forest degradation elsewhere as a result of international trade.

· Design and implement procurement procedures that prioritize sustainable products and services over other alternatives.

· Facilitate development of efficient systems to reuse and recycle (forest) products and avoid landfilling.

· Foster research activities to improve the understanding of substitution effects at product and market level for all product categories, all along the life cycle.

· Strengthen cooperation between scientific, industrial and financing actors to achieve shorter technological innovation cycles.

· Upgrade educational curricula at all levels to encourage sustainability thinking.

· Develop training and capacity building for professionals to update their knowledge of climate-smart and sustainable options.

· Improve consumer awareness by providing accurate and clear information on the possibilities and advantages of sustainable consumption pattern

We do not need to, nor should we, manage every acre in the same way. When it comes to carbon and climate change, we must look at what ultimately reduces atmospheric GHGs in their totality, which can be done by using more wood AND growing more trees.

[1] Breakdown for 2015 as follows: Iron steel, aluminum and other metals emitting 4.8Gt CO2e/yr., followed by cement, lime, plaster and other non-metallic minerals at 4.4Gt CO2e/yr., plastics and rubber emitting 1.5Gt CO2e/yr., wood production 0.9 Gt CO2e/yr. (IRP 2020)


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