Adequately addressing climate change will require a diverse set of approaches to both mitigation and sequestration of carbon emissions. Recently, carbon dioxide removal (CDR) has become an increasingly important climate change mitigation strategy that depends on the ability to store carbon for long time periods. Forest carbon sequestration represents a key CDR opportunity that is regularly highlighted in academic literature and policy. But carbon stored in forests is inherently dynamic: both social and natural disturbances contribute to the flux of carbon from forests. In many forests, these disturbance events are expected to increase into the future, particularly with climate change. Forest management interventions like thinning, prescribed burning, and species selection can mitigate natural disturbance risks, but these strategies often release carbon in the short term and will have to evolve in the long term as climate change disrupts the resilience of forest ecosystems. Carbon stored in harvested wood products (HWPs) has the potential to be durable for decades to 100’s of years, but the durability of carbon stored in HWPs is highly variable and depends on numerous factors that are difficult to accurately quantify. Forests play a key role across the spectrum of CDR opportunities, from reforestation to bioenergy with carbon capture and storage (BECCS). Throughout this dissertation, I work to understand the full carbon life cycle of some of these strategies and the implications for climate change mitigation efforts. This dissertation focuses predominantly on questions of carbon storage, both in disturbance-prone forests and in various forms of harvested wood use. In the first project, I analyze wildfire risk, carbon storage in forests, and innovative uses of low-value wood residues. In the second project, I consider temporal accounting issues in HWPs. And in the third project, I consider the HWP life cycle at a global scale to identify opportunities for climate change mitigation. Although these projects cover a wide breadth of topical and regional emphasis, they are all linked in their shared motivation to understand carbon storage in HWPs as a critical component of forest carbon systems.
In Project 1, I consider the carbon implications of existing forest management goals and the potential impact of increased use of emerging wood products. Specifically, I assess the State of California’s stated goal to treat 1 million acres of forest per year for fire hazard reduction, alongside its aggressive commitments to economy-wide carbon neutrality. Some research has suggested that forest treatment is at odds with climate goals. Treatments are often costly, and large amounts of low-value wood are often burnt or left to decay. Here, I assess climate and wildfire outcomes across several wood use and forest management scenarios. I find that with a suite of innovative wood uses, increased management and wood use could yield net climate benefits between 5.4-15.9 million tonnes of carbon dioxide equivalent (Mt CO2e) per year when considering impacts from management, wildfire, carbon storage in products, and displacement of fossil-intensive alternatives. I find that products with durable carbon storage confer the greatest benefits, including traditional timber products and products with carbon capture and storage. Concurrently, I find that treatment could reduce wildfire hazard on 12.1M acres, 3.1M of which could experience stand-replacing effects without treatment. My results suggest a low-cost pathway to support California's climate adaptation and mitigation goals.
In Project 2, I consider the impact of simplified HWP accounting in a prominent forest carbon offset protocol. In Improved Forest Management (IFM) carbon offset projects registered under the California Air Resources Board Forest Carbon Protocol, carbon offset credits are generated against a baseline which represents counterfactual carbon storage in-forest and in wood products without offset revenue. Often, the chosen baseline for in-forest carbon stocks is well below the initial carbon stocks and, as a result, most projects generate a large proportion of lifetime credits in the first year. Further, the protocols produce baselines that are static through time. This is problematic because carbon in harvested wood changes over time as products go out of use and decay. To simplify the accounting, offset protocols take a single point in time as representative – the average of 100 years of decay. This simplification underestimates the carbon stored in harvested wood products in the counterfactual, resulting in project over-crediting. I find this simplified accounting yields 42 MtCO2e of credits generated too early, nearly half of the credits in the study sample. Using a static baseline underestimates carbon stored in wood products initially and overestimates carbon stored at the end of the project. Functionally, this error delays the climate benefits of the program by offsetting fossil fuel emissions today with emissions reductions that won’t be realized for decades.
In Project 3, I expand the aperture of these questions to a global scale and consider the global life cycle of HWPs and the potential for climate change mitigation interventions in that life cycle. Multiple studies have investigated components of the global HWP life cycle, but none have considered the full life cycle of HWPs from gate to grave for all HWP categories or the potential role of emerging carbon capture technologies in the global HWP lifecycle. In this project, I model carbon emissions and carbon storage for all HWPs at a country scale, including production emissions, the product use phase, and product end-of-life. Following this, I model potential interventions to store carbon or reduce emissions in the HWP life cycle. I find that the global HWP sector is a net carbon sink in 2020 but, with implementation of CCS at mills could become a sink of 3.3 Gt CO2¬/yr by 2050, not counting methane emissions which are uncertain but likely large. Approximately half of this sink would be attributed to baseline carbon storage in products and landfills, and the other half could be realized through CCS. In total, CCS of biogenic CO2 could reach 1.2-1.8 Gt CO2¬/yr by 2050, most of which would be at pulp and paper mills. I conclude that retrofitting existing mills with CCS is a potentially low-cost application of BECCS technologies that requires minimal new infrastructure and little additional biomass feedstock.
