Publications

Submitted
Hammer, Chad F., and John S. Gunn. “Terrestrial Invasive Plant Impacts on Northern Temperate Riparian Forest and Stream Physical Habitat.” Biological Invasions (Submitted).
2020
Gunn, John S., Mark J. Ducey, Thomas Buchholz, and Ethan Belair. “Forest Carbon Resilience of Eastern Spruce Budworm (Choristoneura fumiferana) Salvage Harvesting in the Northeastern United States.” Frontiers in Forests and Global Change 3, no. 14 (2020): 1-13. Publisher's Version Abstract

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.

 

2019
Asbjornsen, H., J. L. Campbell, A.W. D'Amato, J. Garnas, J. S. Gunn, L. R. Iverson, T. A. Ontl, N. Pederson, M.P. Peters, and P. D. Shannon. “Forest management options for addressing drought in the Midwest and Northeast U.S.” In Effects of drought on forests and rangelands in the United States: translating science into management responses. Gen. Tech. Rep. WO-98:227. Washington, DC: U.S. Department of Agriculture Forest Service, Washington Office, 2019. Publisher's Version
Buchholz, Thomas, William Keeton, and John S. Gunn. “Economics of integrated harvests with biomass for energy in non-industrial forests in the northeastern US forest.” Forest Policy and Economics 109, no. December (2019). Publisher's Version Abstract
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.
Gunn, John S., Mark J. Ducey, and Ethan Belair. “ Evaluating degradation in a North American temperate forest .” Forest Ecology and Management 432 (2019): 415-426. Publisher's Version Abstract

 

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. 

 

2018
Moghaddas, J.J., G.B. Roller, J.W. Long, D.S. Saah, M.A. Moritz, D.T. Stark, D.A. Schmidt, et al. Fuel Treatment for Forest Resilience and Climate Mitigation: A Critical Review for Coniferous Forests of California. ,” 2018, CNRA-CCC4A-2018-017, 74. Publisher's Version
Gunn, John S., and David Orwig. “ Old-growth forests under threat: changing dynamics due to invasive plants, pests and pathogens .” In Ecology and Recovery of Eastern Old-Growth Forests, 288pp. Island Press, 2018. Publisher's Version

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.

2017
Gunn, John. “ Assessing the Climate Benefits of Wood Heat .” Pellet Mill Magazine, 2017, 7, 6, 7. Publisher's Version
Gunn, John S. Woody Biomass Energy Emissions: We Still Need to Do the Math .” The Forestry Source September 2017 (2017). Publisher's Version
Buchholz, Thomas, John S. Gunn, and David Saah. “ Greenhouse gas emissions of local wood pellet heat from Northeastern US forests .” Energy 141 (2017): 483-491. Publisher's Version Abstract

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.

preprint
2016
Buchholz, Thomas, Matthew Hurteau, John S. Gunn, and David Saah. “ A global meta-analysis of forest bioenergy greenhouse gas emission accounting studies .” Global Change Biology - Bioenergy 8, no. 2 (2016): 281-289. Open Access
Cheng, Anthony S, R.J. Gutierrez, Scott Cashen, Dennis R. Becker, John S. Gunn, Amy Merrill, David Ganz, Michael Liquori, David Saah, and William Price. “ Is there a place for legislating collaborative forestry? Examining the Herger-Feinstein Quincy Library Group Forest Recovery Act Pilot Project .” Journal of Forestry 114, no. 4 (2016): 494-504. Publisher's Version
2015
Matzek, Virginia, Cedric Puleston, and John S. Gunn. “ Can carbon credits fund riparian forest restoration? .” Restoration Ecology 23, no. 1 (2015): 7-14. Publisher's Version
2014
Gunn, John S., Mark J. Ducey, and Andrew A. Whitman. “ Late-Successional and Old-Growth Forest Carbon Temporal Dynamics in the Northern Forest (Northeastern USA) .” Forest Ecology and Management 312 (2014): 40-46. Publisher's Version