Five years ago, Adam Young used paleofire evidence to hypothesize how climate warming would affect future tundra fires in Alaska. Adam basically predicted a big increase in tundra fire occurrence if the average July temperature warmed above a threshold of 13.4°C (56°F: Young, et al. 2017). This year, Arif Masrur et al. (2022) provided important evidence corroborating Adam’s theory using modern fire and climate records. The research team use machine learning to determine the relative importance of various climate, prior burn history, and biophysical values on tundra fire occurrence and size. They also tapped the rich collection of field plot data collected by the National Park Service and other management agencies for vegetation characteristics and verification of reburn status. Arif did, indeed, find a strong increase in recent Alaskan tundra fires concurrent with much warmer summers. Annual tundra burned area has almost doubled and reburned area has increased by 61% since 2010! The study also revealed a small but significant feedback effect of previous tundra fires on reburning, validating management strategies like using prescribed fire to reduce wildfire threat near villages.
Young, AM, Higuera PE, Duffy PA and Hu FS. 2017. Climatic thresholds shape northern high-latitude fire regimes and imply vulnerability to future climate change Ecography 40:606–17. Slides and recording from Adam’s 2019 presentation on this study HERE: https://www.frames.gov/catalog/60348
See also p. 24 WFOctNovDec2022 for updates on fuel break projects on the Kenai by Tracy Robillard.
Please also note a great Post-Doc opportunity with one of AFSC’s collaborating scientists to study boreal climate change impacts and mitigation methods. It pays well (~$68,000 year for two years) and comes with a lot of flexibility and opportunities for global scale collaboration. The ad is here: https://www.edf.org/jobs/cooley-postdoctoral-science-fellow
Jordan Smith and Chase Lamborn, from Utah State University, recently completed a study of fire impacts on fishing in the Kenai River from the 2019 Swan Lake fire. Their study–funded by the Joint Fire Science Program— combined a literature review with interviews of local experts to identify impacts. The Kenai River is important: not only is it the most popular sportfishing destination in Alaska, averaging 275,000 angler days per year, it also produces 1/3 of the commercial salmon harvest in the Cook Inlet basin. Smith interviewed a small but diverse group of stakeholders who had extensive experience with the KR watershed, including agency resource managers, fishing advocates, people from non-profits, tribal members, and business owners. In addition to fire impacts, the study established a model of the Kenai River as a social-ecological system, which could be used to determine impacts from other kinds of disturbance.
Interviewees pointed out that a certain amount of luck, such as the lack of heavy rains post-fire to add big sediment loads as well as the fire’s location missing key Chinook spawning watersheds—limited any direct reported impacts of fire on fish. There were, however, impacts to resource users and businesses—primarily due visitors avoiding the area and road/river closures which restricted access during a brief, but critical, period of the summer. Nevertheless, a terrific early 2019 sockeye run (3-5x above preceding few years) helped to offset impacts on the sport fishery by encouraging anglers with high bag limits and success rates.
The literature review part of the study highlighted potential impacts to rearing and spawning habitats, water quality and fish passage. Most sobering are examples where populations failed to recover after fire, but these are the exception, not the rule. Adverse impacts are most likely from high-severity fires becasue they can lead to erosion and flooding. These events can induce loss of stream fishes, and generally require 3-10 years to recover when spawning habitat is affected. For the Kenai River, early-run chinook salmon were identified as the most vulnerable to this type of event. Although Smith et al. did not directly measure water temperature, stream flow, sediments, or mercury levels following fire on the Kenai, they provide a useful literature review of examples from elsewhere. They point out that with stream temperatures increasing and flows decreasing in the western continental US (a combination which can be deadly for fish), the threat of fire-related warming may become more serious in the future than it has been in the past.
To thwart runaway climate warming, the global community is struggling to find strategies to limit carbon dioxide (CO2) emissions that are steeply climbing. Increasing boreal wildfires in Alaska and Canada also threaten to increase CO2 emissions and could contribute potentially 12 gigatons to the world’s carbon headache by mid-century.
Fire Management strategy could make a difference: A research team from The Woodwell Climate Research Center and Union of Concerned Scientists wondered whether fire management offered a realistic way to slow down the release of legacy carbon in boreal forests, giving Nature and humans time to adapt and implement other mitigation strategies. How much would it cost to keep Alaskan wildfires at their historic level, avoiding climate-induced predicted increases? And was it even possible to make a difference? In short, the study found that—yes—more fire suppression could keep nearly 1/3 (4 Gt ) of that carbon in the ground in Alaska and Canada. The study tries to estimate costs associated with carbon savings and compares them to other carbon-sparing strategies being used or planned. Project goals are below are from a presentation given to Alaskan fire managers last fall.
Download our short Research Brief above (and/or you can access the full scientific article, open access, HERE:
Phillips, et al. 2022.
Escalating carbon emissions from North American boreal forest wildfires and the climate mitigation potential of fire management.
The face of a scientist: does that conjure an image of a certain gender, race, and age? Albert Einstein perhaps? Those stereotypes are changing: meet Dr. Yaping Chen–a rising star of science with a spectacular track record. The last 3 years she has come up with one mind-boggling revelation after another about how fire works in the Alaska tundra. After a MS degree in environmental engineering in China, Dr. Chen completed her PhD in the lab of the venerable Dr. Feng Sheng Hu at the University of Illinois. I first met her presenting a poster on the Nimrod Hill fire (Imuruk Lake, on the Seward Peninsula) at an American Geophysical Union meeting in 2019. The work was novel, ingenious, and suggestive of new ways to study fires with new computational and remote sensing tools. That was just the tip of the iceberg–or the thermokarst, if you will! Since then Dr. Chen has published numerous diverse research studies improving our understanding of dueling post-fire successional trajectories in tundra, improved burn severity mapping of legacy tundra fires, and fire regime effects on carbon balance. Her most recent paper outlines the role of tundra fire vs. climate warming in thawing permafrost in Alaska tundra statewide! If you’ve missed any of these important papers for your collection, links are included below. Now Dr. Chen is a post-doctoral researcher at the Virginia Institute of Marine Science, continuing her work on unraveling impacts of climate change. Thank you, Dr. Chen for all you’ve revealed to us in Alaska!
In one handy paper that came out in 2021, Alaska fire analysts Robert “Zeke” Ziel and Chris Moore have compiled how-to’s, resources, fuel model-to-vegetation type crosswalks, and pro tips and secrets. The reference takes you all the way from introduction to the Canadian Forest Fire Danger Rating system to how to conduct an analysis of fire behavior in WFDSS (Wildfire Decision Support System used by fire agencies). Included are such perplexing topics as how to estimate live and dead fuel moisture, what are the available short-term and near-term fire models, what do do about winds, which National fuel models require “tweaking” in Alaska, and sources of vegetation map products and satellite imagery. Fire behavior analysts definitely want to review this before the fire season and make sure it’s handy in their kit if they plan to work in Alaska, and researchers will also find this an extremely useful state-of-the-art comprehensive review of how fire behavior analysis currently works in practice.
From the authors: “Alaska is faced with a unique fire management problem that has been handled in an interagency way for more than 30 years. The evolution of fire management has led to a different approach in interagency cooperation; weather data management; fire behavior and fire danger implementation; GIS management; and overall fire suppression strategies. This guide is intended to provide standardized inputs for initial analysis; these are not hard and fast rules to be strictly followed throughout an incident.”
At the November, 2021 Association of Fire Ecology Conference, Erin Belval from the USFS Rocky Mountain Research Station summarized results of surveys conducted with interagency hotshot crews, tallying their assessment of the effectiveness of several measures used to mitigate the spread of Covid-19 in 2020. For example, most respondents said they preferred virtual check-in and paperwork (although 25% had some problems with it). Fully 75% of respondents thought virtual briefings were as effective as in person and/or saved time. When asked: “Did you prefer the single large incident command post (ICP), or spike camps or multiple smaller operating bases?” crews showed a strong preference for spiking out on the line, with the resources of a full ICP supporting them. The presentation was titled Interagency Hotshot Crews views of new practices developed to address COVID-19 and you can view it on YouTube (one of several presentations available from a social and ecological resilience to wildfire session) HERE>>>>>: https://www.youtube.com/watch?v=hoGdcP9GTyU&t=4763s
A new study just published in Sustainability surveyed Fairbanks Northstar Borough and Kenai Peninsula Borough homeowners about their willingness to pay for types of fuelbreaks on their property, their neighbor’s property and how public land treatments nearby affected their choices. Molina et al. found that surveyed homeowners (n=358) had a greater willingness-to-pay for fire hazard reduction when a moderate number of neighbors (1-4 neighbors) engaged in property mitigation. They were less enthusiastic when nobody else was participating, or on the other hand–when they perceived too many neighbors were clearing fuels. Shaded fuel breaks–like thinning treatments–were preferred to clearcutting. Read the article (open access) here: https://www.mdpi.com/2071-1050/13/21/11754/htm
Molina A, Little J, Drury S, Jandt R. Homeowner Preferences for Wildfire Risk Mitigation in the Alaskan Wildland Urban Interface. Sustainability. 2021; 13(21):11754. https://doi.org/10.3390/su132111754
Forestry research in Alaska indicates that coniferous-dominated interior boreal forests are being replaced by deciduous trees due to recent climate warming and changes in the wildfire regime. Mann et al. 20121 suggested a dramatic shift in forest species dominance was already happening, since the 1990’s. Interior Alaska forests have averaged about ⅔ coniferous to ⅓ deciduous over the last several hundred years. Using landscape disturbance models under various global climate scenarios, Mann’s team predicted the ratio would soon be 1:1 and even reverse by mid-century, with hardwood stands comprising ⅔ of the forests. Now, 30 years of satellite imagery and improved vegetation mapping methods using new technology offer a chance to test their predictions.
Post-fire succession: When Alaska spruce forests burn the trees are killed, but black spruce stands tend to “self-replace” about ⅔ of the time—by seeding into the remnant moss layers2. On the other hand, it has been well-documented that “severe” (deep-burning) forest fires favor regrowth of hardwoods (birch, aspen and poplar). These species can grow fast in deeper active layers that result after severe fires in which most of the moss duff is removed3. This can result in a “relay succession” recovery where hardwoods dominate the canopy for a time before slower growing spruce can regain dominance of the canopy. In either case, if the stand reburns within about 50 years, small black spruce in the understory are destroyed before developing a robust seed bank, and the stands tend to become increasingly hardwood dominated. Ongoing studies to refine these parameters in eastern interior Alaska reveal that pure black spruce stands transitioned to deciduous forest about half the time after a severe fire4. Coniferous forest with even a small percentage of deciduous stems (> 7%) succeeded into a mixed-wood composition (50:50) and stands which had >30% pre-fire deciduous stems became exclusively deciduous.
Why is a shift in forest species important? Spruce forests have vastly different properties than broadleaf forests. These differences include: higher flammability, lower water uptake, slower litter decomposition rates, different atmospheric heating properties (surface albedo), and carbon sequestration capacity. Of course, they also differ with respect to supplying wood, game, and berries to humans. Black spruce trees thrive in cold, moist soil conditions, and actually enhance these conditions by accumulating a deep mossy soil organic layer. The moss layer is often too moist–with snowmelt water, rainfall, and seasonally thawing ice below–to support combustion beyond a few centimeters deep. Most of the carbon (C) stored in these slow-growing forests is in the moss and soil organic layers. Warmer summers and extended burning seasons in late summer tend to allow the moss duff layers to dry faster and deeper. In western Canada, 90% of C combusted in extensive 2014 fires in black spruce forest came from the forest floor 5. Deciduous trees, on the other hand, thrive in nutrient rich, dry and (relatively) warm soils, and reinforce these conditions with high decomposition rates, so the soil organic layer tends to be shallow. Their faster growth rate (productivity 5-7 times greater than black spruce forest) means that they store most of their C aboveground in the trees themselves6. Deciduous trees also require more water to sustain that rapid growth—a lot more! It was recently discovered that Alaska broadleaf trees take up 25% of available spring snowmelt water (compared to about 1% for spruce)7. But mature spruce forests (aged 70-120 years) win out when it comes to long-term C storage — they had 4-10 times the C stored in their organic soils (2.0-5.7 kg C m-2) compared to 50-year-old stands8.
Was the forest shift prediction accurate? Back to the changing forest composition. What does the latest research tell us about the predictions of a decade ago? As part of a multi-year NASA study, Wang, et al. 20209 used an enormous data set of satellite-derived vegetation cover type estimates covering all Alaska and northwestern Canada from 1984 to 20149. They documented a net loss of 14.7% (+/- 3%) coniferous forest along with an equivalent net gain of deciduous forest. These results seem consistent with the predicted forest composition shift caused by a more active fire regime in boreal forests relative to the last several millennia. In an ongoing separate study, preliminary data showed that in burned areas of the boreal biome the ratio of deciduous to evergreen forest cover increased 14.4% (from 23.4% to 37.8%) from 2001-2016, which was 3.3 times higher than in unburned areas10. However, these same authors also documented that mixed and deciduous forest types may be burning more now compared to previous decades, perhaps even burning at a faster rate than they were being replaced during the study time window. In addition, by coupling two types of remotely sensed data for vegetation, the researchers could estimate forest biomass and tree-canopy structure. This analysis showed that recovering burned forest, whether it succeeded to deciduous forest or remained evergreen, still had overall lower biomass and canopy density compared to areas that did not burn. This finding has implications for management scenarios involving fire use to reduce future fuel loadings, and also for carbon sequestration studies. Separate investigations confirm the loss of forest biomass across eastern interior Alaska and predict this will become the modern trend as the climate warms4. Impacts on wildfire and permafrost dynamics will result in overall decreases in biomass (particularly for spruce within the interior Tanana Valley, despite increases in quaking aspen biomass) and result in a continued shift towards a higher deciduous fraction. To a lesser extent, increased biomass is seen at certain locations, such as cold or wet locations, and at high elevations, such as along the north slopes of the Alaska range11. In summary, recent studies seem to support the predictions made a decade ago1 with respect to spruce forest declining and broadleaf and mixed forest increasing across interior Alaska.
What about negative feedbacks to boreal burning? Deciduous forests are more resistant to fires than spruce forests—a guiding principle of much fire suppression and fuel treatments strategy12. Under average summer conditions, coniferous forest is more conducive to large fire spread and accounts for at least half of the average yearly burned extent. Since hardwood forests are less flammable, why doesn’t a negative feedback kick in to reduce flammability as deciduous forests become more common on the landscape? The short answer is that most mega-fires burn in unusually hot/dry summers, and once the fire weather gets extreme enough, deciduous forests and regenerating forests become equally receptive to burning13. The “unusual” heat is becoming more “usual” in recent decades, and future climate scenarios predict dramatic increases in high fire danger days. As for the future of forests in Alaska, new models at the stand level are being developed which include the latest understanding of forest environmental drivers and physiological constraints4,11. A research study funded by the Department of Defense in eastern interior will be sharing findings regarding fire-prone areas of Alaska from Fairbanks to the Canadian border, complete with web visualization tools for managers (beta version: https://masseyr44.users.earthengine.app/view/decidfractreecoverserdpv1).
The takeaway: Alaska’s boreal forest is undergoing major changes driven by the domino effects of changing climate. Boreal forests are experiencing changes in the fire regime, which through interactions with the ecological and physiological attributes of trees are causing widespread shifts in forest composition. Those shifts in turn are causing a shift towards net C release to the atmosphere which could accelerate global warming. Overall, these shifts in forest species dominance are a fascinating example of how even a relatively simple biome like boreal forest can have complex responses to changes in climate.
Acknowledgements: Many thanks to Dr. Dan Mann and Dr. Eric Deutsch for helpful discussion and interpretation and to Zav Grabinski for editing help.
References: 1 Mann, D. H., T. S. Rupp, M. A. Olson, and P. A. Duffy. 2012. Is Alaska’s boreal forest now crossing a major ecological threshold? Arctic Antarctic and Alpine Research, v. 44, no. 3, p. 319-331.
2 Baltzer, Jennifer et al. 2019. Widespread ecological reorganization of boreal forests following severe wildfires. AGU Poster B33B-07, San Francisco, CA Dec. 9-12, 2019.
3 Hollingsworth, T. N., J. F. Johnstone, E.L. Bernhardt, S. F. Chapin. 2013. Fire severity filters regeneration traits to shape community assembly in Alaska’s boreal forest. Plos One 8(2):e56033.
4 Goetz, Scott, et al. (ongoing) SERDP Project RC18-C2-1183: Resiliency and Vulnerability of Boreal Forest Habitat across DoD Lands of Interior Alaska.
5 Walker, X. et al. 2018. Cross-scale controls on carbon emissions from boreal forest megafires. Global Change Biology 24 (9): 4251-4265.
6 Alexander, H. and M. Mack. 2016. A Canopy Shift in Interior Alaskan Boreal Forests: Consequences for Above and Belowground Carbon and Nitrogen Pools during Post-fire Succession. Ecosystems 19: 98-114.
7 Young-Robertson, J. M., W.R. Bolton, U.S. Bhatt, J. Cristóbal, R. Thoman. 2016. Deciduous trees are a large and overlooked sink for snowmelt water in the boreal forest. Scientific Reports 6:29504.
8 Hoy, E.E., M.R. Turetsky and E.S. Kasischke. 2016. More frequent burning increases vulnerability of Alaskan boreal black spruce forests. Environ. Res. Lett.11 095001
9 Wang, J. A., D. Sulla-Menashe, C.E. Woodcock, O. Sonnentag, R.F. Keeling and M.A. Friedl. 2020. Extensive Land Cover Change Across Arctic-Boreal Northwestern North America from Disturbance and Climate Forcing. Global Change Biology 26, 807–822.
10 Deutsch, E.J. and M.L. Chipman. 2020. Observations of Post-Wildfire Land Cover Trends in Boreal Alaska Using Geospatial Analyses. AGU Poster, Virtual, Dec. 1-17, 2020.
11 Foster, A.C. et al. 2019. Importance of tree- and species-level interactions with wildfire, climate, and soils in interior Alaska: Implications for forest change under a warming climate. Ecol. Modeling 409: 108765.
12 Beverly, J. L. 2017. Time since prior wildfire affects subsequent fire containment in black spruce. International Journal of Wildland Fire 26:919–929.
13 Barrett, K, T. Loboda, A.D. McGuire, H. Genet, E. Hoy, and E. Kasischke. 2016. Static and dynamic controls on fire activity at moderate spatial and temporal scales in the Alaskan boreal forest. Ecosphere7(11): e01572. 10.1002/ecs2.1572.
14 Dash, C.B., J.M. Fraterrigo, and F.S. Hu. 2016. Land cover influences boreal forest fire responses to climate change: geospatial analysis of historical records from Alaska. Landscape Ecology 31:1781–1793.
A pair of new 2021 papers take different tracks to assess the impact of human activities and anthropogenic climate warming, on fire season in south central Alaska. We still remember how smoke choked the Kenai and Matsu boroughs in 2019, for most of June-August. A University of Alaska team tallies the impacts–in $$, losses, and human health, while also placing the season in a historical context to look for anthropogenic influence. They deemed human influences thus far were less important than weather, but would become more of a factor by mid-century. An important finding was that heating seemed to overpower increased precipitation (over longer timescales): “The effect of warming temperatures dominates the effect of enhanced precipitation in the trend towards increased fire risk.” Read the full paper HERE: Uma S. Bhatt, et al. 2021. Emerging Anthropogenic Influences on the Southcentral Alaska Temperature and Precipitation Extremes and Related Fires in 2019. Land. 2021; 10(1):82. https://doi.org/10.3390/land10010082