Development of the bioenergy sector is being actively pursued in many countries
as a means to reduce climate change and fulfill international climate agreements
such as the Paris Agreement. Although biomass for energy production (especially
wood pellets) can replace carbon-intensive
fossil fuels, its net greenhouse gas impact
varies, and the production of wood pellets can also lead to intensification in
forest harvests and reduction of forest carbon stocks. Additionally, under specific
conditions, emissions associated with imported biomass feedstocks may be omitted
from national accounts, due to incompatibilities in accounting approaches. We
assessed the risks and potential scale of emissions omitted from accounts (EOA)
among key trading regions, focusing on the demand for wood pellets under different
levels of climate mitigation targets. Our results suggest that the global production
of wood pellets would grow from 38.9 to 120 Mton/year between 2019 and
2050 in a scenario that limits global mean temperature increase to 1.5°C above
pre-industrial
levels. A large portion of this occurs in North America (36.8 Mton/
year by 2050), Europe (47.6 Mton/year by 2050), and Asia (23.3 Mton/year by
2050). We estimate that in a 1.5°C scenario, global EOA associated with international
trade of wood pellets has the potential to reach 23.81 MtCO2eq/year by
2030 and 69.52 MtCO2eq/year in 2050. Emissions resulting from European biomass
energy production, based on wood pellet imports from the United States,
may reach 11.68 MtCO2eq/year by 2030 and 33.57 MtCO2eq/year in 2050. The
production of wood pellet feedstocks may also present a substantial carbon price
arbitrage opportunity for bioenergy producers through a conjunction of two distinct
GHG accounting rules. If this opportunity is realized, it could accelerate the
growth of the bioenergy industry to levels that harm forests’ function as a carbon
sink and omit actual emissions in national and global accounting frameworks.

Forest carbon offset protocols reward measurable carbon stocks to adhere to accepted greenhouse gas (GHG) accounting principles. This focus on measurable stocks threatens permanence and shifts project-level risks from natural disturbances to an offset registry’s buffer pool. This creates bias towards current GHG benefits, where greater but potentially high-risk stocks are incentivized vs. medium-term to long-term benefits of reduced but more stable stocks. We propose a probability-based accounting framework that allows for more complete risk accounting for forest carbon while still adhering to International Organization for Standardization (ISO) GHG accounting principles. We identify structural obstacles to endorsement of probability-based accounting in current carbon offset protocols and demonstrate through a case study how to overcome these obstacles without violating ISO GHG principles. The case study is the use of forest restoration treatments in fire-adapted forests that stabilize forest carbon and potentially avoid future wildfire emissions. Under current carbon offset protocols, these treatments are excluded since carbon stocks are lowered initially. This limitation is not per se required by ISO’s GHG accounting principles. We outline how real, permanent, and verifiable GHG benefits can be accounted for through a probability-based framework that lowers stressors on a registry’s buffer pool.

Non-native invasive plant species are a major cause of ecosystem degradation and impairment of ecosystem service benefits in the United States. Forested riparian areas provide many ecosystem service benefits and are vital to maintaining water quality of streams and rivers. These systems are also vulnerable to natural disturbances and invasion by non-native plants. We assessed the effects of planting native trees on disturbed riparian sites and their ability to resist invasive plants in central Vermont in the northeastern United States. The density (stems/m²) of invasive stems was higher in non-planted sites (x̄=4.1 stems/m²) compared to planted sites (x̄=1.3 stems/m²) More than 90% of the invasive plants were Japanese knotweed (Fallopia japonica). There were no statistically significant differences in total stem density of native vegetation between planted and non-planted sites. Other measured response variables such as native tree regeneration, soil properties and soil function showed no statistically significant differences or trends in the paired riparian study sites. The results of this case study indicate that tree planting in disturbed riparian forest areas may assist conservation efforts by minimizing the risk of invasive plant colonization.

Increasing demand for woody biomass-derived electricity in the UK and elsewhere has resulted in a rapidly expanding wood pellet manufacturing industry in the southern US. Since this demand is driven by climate concerns and an objective to lower greenhouse gas (GHG) emissions from the electricity sector, it is crucial to understand the full carbon consequences of wood pellet sourcing, processing, and utilization. We performed a comparative carbon life cycle assessment (LCA) for pellets sourced from three mills in the southern US destined for electricity generation in the UK. The baseline assumptions included GHG emissions of the UK’s 2018 and 2025 target electricity grid mix and feedstock supplied primarily from non-industrial private forest (NIPF) pine plantations augmented with a fraction of sawmill residues. Based on regional expert input, we concluded that forest management practices on the NIPF pine plantations would include timely thinning harvest treatments in the presence of pellet demand. The LCA analysis included landscape carbon stock changes based on USDA Forest Service Forest Vegetation Simulator using current USDA Forest Service Forest Inventory and Analysis data as the starting condition of supply areas in Arkansas, Louisiana and Mississippi. We found that GHG emission parity (i.e., the time when accumulated carbon GHG emissions for the bioenergy scenario equal the baseline scenario) is more than 40 years for pellets produced at each individual pellet mill and for all three pellet mills combined when compared to either the UK’s 2018 electricity grid mix or the UK’s targeted electricity grid mix in 2025. The urgency to mitigate climate change with near-term actions as well as increasing uncertainty with longer-term simulations dictated a focus on the next four decades in the analysis. Even at 50% sawmill residues, GHG emission parity was not reached during the 40 years modeled. Results are most likely conservative since we assume a high share of sawmill residues (ranging from 20% to 50%) and did not include limited hardwood feedstocks as reported in the supply chain which are generally associated with delayed GHG emission parity because of lower growth rates.

The next major eastern spruce budworm (Choristoneura fumiferana) outbreak is likely to begin impacting the forests of the northeastern US over the next few years. More than 4.7 million ha of forest and 94.8 million Mg of carbon in spruce (Picea spp.) and balsam fir (Abies balsamea) are at risk. Vegetation shifts in at-risk forest stands are likely to occur as a direct result of mortality caused by spruce budworm and through post-outbreak salvage harvest operations designed to minimize economic impact. Management interventions have short-term and long-term consequences for the terrestrial carbon budget and have significant implications for the role of the region’s forests as a natural climate solution. We used regional forest inventory data and 40-year growth and harvest simulations from the USDA Forest Service Forest Vegetation Simulator to quantify a range of forest carbon outcomes for alternative silvicultural interventions in the northeastern US. We performed a life cycle assessment of harvested wood products, including bioenergy, to evaluate the full greenhouse gas (GHG) emissions consequences of salvage and business as usual silvicultural scenarios across a range of stand risk profiles in the presence and absence of spruce budworm attack. Salvaging dead trees in the most at-risk stands tends to produce net emissions of carbon dioxide for at least ten years compared to a baseline where dead trees are left standing. In most scenarios, GHG emissions reached parity with the baseline by year 20. Changes in forest carbon stocks were the biggest driver of net emission differences between salvage and no salvage scenarios. A benchmark scenario without timber harvesting or the occurrence of a spruce budworm outbreak had the greatest net carbon sequestration profile after 40 years compared to all other scenarios. Salvaging trees killed by a severe and widespread insect infestation has potential negative short-term implications for GHG emissions, but long-term resilience of these climate benefits is possible in the absence of future outbreaks or subsequent harvest activities. The results provide guidance on silvicultural interventions to minimize the impact of spruce budworm on forest carbon.

The next major eastern spruce budworm (Choristoneura fumiferana) outbreak is likely to begin impacting the Northern Forest region of the northeastern US over the next few years. More than 4.7 million ha of forest and 94.8 million Mg of carbon in spruce (Picea spp.) and balsam fir (Abies balsamea) are at risk. Vegetation shifts in at-risk forest stands are likely to occur as a direct result of mortality caused by spruce budworm and through anthropogenic response to an outbreak through salvage harvest operations designed to minimize economic impact. Management interventions have short-term and long-term consequences for the terrestrial carbon budget and have significant implications for the role of the region’s forests as a natural climate solution. We used regional forest inventory data and 40-year growth and harvest simulations from the Forest Vegetation Simulator to quantify a range of forest carbon outcomes for alternative silvicultural interventions in the Northern Forest. We performed a life cycle assessment of harvested wood products, including bioenergy, to evaluate the full carbon consequences of salvage and business as usual silvicultural scenarios across a range of stand risk profiles in the presence and absence of spruce budworm attack. Salvaging dead trees in the most at-risk stands tends to produce net emissions of carbon dioxide for at least ten years compared to a baseline where dead trees are left standing. In most scenarios, carbon dioxide emissions reached parity with the baseline by year 20. Changes in forest carbon stocks were the biggest driver of net emission differences between salvage and no salvage scenarios. A benchmark scenario without timber harvesting or the occurrence of a spruce budworm outbreak had the greatest net carbon sequestration profile after 40 years compared to all other scenarios. Salvaging trees killed by a severe and widespread insect infestation has potential negative short-term implications for greenhouse gas emissions, but long-term resilience of these benefits is possible in the absence of future outbreaks or subsequent harvest activities. The results provide guidance on the best strategy for risk management silvicultural interventions to minimize the impact of spruce budworm on both forest product and the resilience of carbon values in the forest.

 

Economic drivers explaining the harvest of biomass for energy use in northeastern forests in the United States arenot well understood. However, knowledge of these drivers is essential for bioenergy policy development, bio-mass supply estimates, and assessments of harvesting impacts on forest ecosystems and carbon stocks. Usingempirical data from 35 integrated harvest sites in northeastern US non-industrial forests, we analyzed theeconomics of mixed wood product logging operations that included biomass for energetic use from both land-owner and logging contractor perspectives. Results were highly variable but indicate that biomass harvest re-moval intensities were not explained by primary forest management objectives, harvest area, or harvested woodproduct quantity. Rather than harvest area or choice of machinery, we identified biomass harvest intensity as amain driver of profits for a harvest operation, as measured in hourly and total net income to the logging con-tractor. While biomass stumpage payments to the landowner were marginal, tree bole biomass constituted morethan half (54%) of the extracted volume by weight, far outweighing biomass derived from tops and limbs only.Biomass harvests, therefore, might encourage logging contractors to intensify harvest removals rather than in-crease harvest area or choose a specific harvest type or method. Such intensification could have beneficial ordetrimental impacts on a stand and needs to be addressed through further studies of potential consequences forbiodiversity and various ecosystem services.

 

Forest degradation has been a focus of recent concern, especially in tropical countries, but temperate forests may also exhibit degradation. Our analysis of US Forest Service Forest Inventory and Analysis data shows that nearly 40% of the forestland in northern New England, U.S.A., (Maine, New Hampshire, and Vermont) is in an understocked condition when species desirability and tree form are considered. This understocked area does not contain sufficient stand-level density of current or potential future sawlog trees, of preferred or secondary commercial species, to be able to fully utilize the growing space of the site following 10 years’ growth (i.e., they are below the “C-line” in a stand stocking guide when desirable trees are considered). Although forests in the region show a slight trend of increased stocking, nearly all this increase comes from shade-tolerant hardwoods (e.g. Fagus grandifolia), trees with poor form (e.g. Acer rubrum), and from Abies balsamea which is subject to episodic eastern spruce budworm (Choristoneura fumiferana) outbreaks. This degraded condition is likely the result of past management activities that have not considered long-term silvicultural objectives and may entail reduced resilience to many climate-related risks for forests and the ecosystem services they provide. Forest management and policy alternatives must be designed and incentivized to restore forest productivity and diversity and to increase climate resilience of the forests in northern New England. 

 

We used a life cycle greenhouse gas (GHG) accounting tool to test the sensitivity of Maine’s state-wide forest sector GHG emissions to changes in forest management. Inputs included forest cover data and growth and yield models for the state of Maine. We estimated net GHG emissions over 100- and 300-year time horizons of different management strategies across a range of carbon (C) pools and emission sources. C pools included: (1) storage in above- and below-ground live and dead biomass; (2) storage in forest products in use and in landfills; (3) harvest, transport, and manufacturing emissions; (4) avoided emissions (substitution, bioenergy); and (5) landfill methane fluxes. Continuation of the baseline forest sector was a net GHG sink throughout the 300-year modelling period. Increasing management intensity through greater use of even-aged management increased total emissions compared with the baseline. Scenarios that increase the area of no harvest set asides compared favourably with baseline GHG emissions predicted for reduced harvesting intensity scenarios when product substitution was not considered. The sensitivity of results to inclusion or exclusion of GHG pools, such as avoided emissions through product substitution, illustrates the importance of assumptions when evaluating complex LCA systems.

We explored greenhouse gas (GHG) implications of locally-sourced and produced wood pellets to heat homes in the US Northern Forest region. Using data from regional pellet industries, forest inventories and harvests, we analyzed pellet GHG emissions across a range of harvest and forest product market scenarios over 50 years. We expanded an existing life cycle assessment (LCA) tool, the Forest Sector Greenhouse Gas Assessment Tool for Maine (ForGATE) to calculate GHG balances associated with the harvest, processing, and use of wood pellets for residential heating vs. alternative heating fuels. Market assumptions and feedstock mix can create diverging GHG emission profiles for pellet heat. Outcomes are predominantly influenced by biogenic carbon fluxes in the forest carbon pool. An industry-average pellet feedstock mix (50% sawmill residues, 50% pulpwood) appeared to generate heat that was at least at parity with fossil-fuel heating alternatives when harvest levels remain unchanged due to pellet production. If harvest levels increase due to pellet production, using pellet heat increased GHG emissions. If baseline harvest levels drop (e.g., following the loss of low-grade markets), GHG emissions from pellet heat would at least remain stable relative to fossil alternatives.