A group of prominent researchers just analyzed data from a large number of burned field sites in Alaska, collected from 2021-2023. The Bonanza Creek Long-Term Ecological Research program at UAF has been funded by the National Science Foundation since 1987 and they have established an impressive network of fire effects plots across interior Alaska. For this analysis on the fate of stored carbon they examined 555 recently (within 7 years) burned plots contained in 31 separate fires across diverse boreal forests, with pre-burn stand ages ranging from 11-254 years. Including the most recent burn, 26 of the sites burned 3 times according to fire records and ecological data.
The analysis indicated that increasing fire frequency and reburning will significantly reduce C storage capacity through progressive consumption of more biomass (mainly duff) with subsequent fire events, as well as shift forested toward non-forested landscapes. Part of the C loss results from the second fire consuming the fallen burned trees from the previous fire. Under the unique conditions that prevail in the boreal landscape, these logs are typically overgrown and buried by moss in a couple decades. There, the cold, acidic environment slows decay so that this wood can be preserved for centuries, but when fire returns to the site quickly the woody debris is consumed before it can be buried in the “bank”.
In short, a recovery period of < 70 years between fire events is not sufficient to reaccumulate C stores in the forest floor between fires and makes it likely that legacy C will be lost with each subsequent fire.
The Alaska Wildland Fire Coordinating Group, representing agencies and land managers involved in managing wildfire has a Fire Research and Applications Committee (FRDAC). Periodically, the committee surveys members and collaborators to see what they consider to be the most important current areas of wildland fire research in the Alaska region. Science providers, in particular, may be interested in this management perspective on research. At last week’s interagency Fall Fire Review, committee chair Jennifer McMillan discussed top-ranked categories of fire effects, fuel treatments, and environmental/land cover change identified by the survey. For example, AWFCG members expressed interest in more research into fire effects on moose/caribou populations, subsistence lifestyles, migration patterns and berry production. For fuel treatments, the areas identified were treatment longevity and effectiveness, maintenance, and biodiversity and habitat responses. Expanded briefs (with citations) on 3 critical research gaps are located on our partner page for FRDAC: https://www.frames.gov/afsc/partners/frdac/research-needs
Many of you will recall the work Badola and Panda have been doing at UAF to test development of low-cost, detailed vegetation maps for boreal Alaska using widely available Sentinel-2 satellite data. Fire managers challenged Anushree Badola (for her PhD work) to make fuels maps that were more accurate than LANDFIRE and better separated black spruce from mixed and deciduous forest types. That work (and her doctorate) was completed last year, and indeed, for the interior Alaska testing site, they appear to be twice as accurate as LANDFIRE at a 30m resolution and do a good job of distinguishing forest types. But did you know that she has made those maps (which cover most of Alaska with the exception of the western end of the Seward Peninsula and the North Slope) available for free download? All is explained succinctly in her STORYMAP and there is also a 2-minute video refresher by Anushree about the project, which was sponsored by National Science Foundation grants and the State of Alaska, with lots of input from the fire management community. Here’s a screenshot from the Storymap as a teaser!
As boreal and arctic ecosystems respond to warming climate, a key question is: will Alaskan landscapes become wetter or drier after fire? Previous studies have shown that, at least for a few years post-fire, organic soil duff has higher moisture content compared to controls, both in boreal forest (Hinzman et al. 2000, Potter & Hugny, 2020) and tundra (Liljedahl, et al. 2007). Liljedahl noted that denser deep organic duff layers remaining after a Seward Peninsula fire had a relatively larger surface area per volume and different pore shape, maybe making them better at retaining water than the pre-burn fluffier upper layers. Yet, over the long term, burn scars tend to become better drained and drier. Hinzman et al. (2000) sampled old burns up to 50 years old and noted “severely burned sites have progressively become drier and warmer resulting in major changes to the vegetation type and soil structure.” What are the drivers of these changes?
Wes Schaefer photo of flux tower on UAF campus. UAF EPSCoR Evapotranspiration Project.
In a recent study, Thunberg et al. 2021 studied factors that drive wetting (precipitation) vs. those that drive drying (evaporation and plant transpiration). Solar radiation speeds evapotranspiration (ET) and relative humidity (RH) slows it down. Thunberg used flux tower data from stations between Fairbanks and Utqiagvik (Barrow) including burnscars from 2004 and 2007. The towers measure greenhouse gas and water fluxes between the land and air. Her study showed ET increased after fire, which could (independent of other factors) indicate a trend toward surface drying. Increased ET was pronounced at a North Slope tundra fire in early years and remained detectable for about 8 years post-fire. ET at Poker Flats forest burn site also exceeded that of an adjacent unburned site during 5/6 years studied. Interestingly, Rocha et al. (2011) linked the early increases in ET at the Anaktuvuk River tundra fire to an increase in evaporation from loss of the spongy moss and organic duff, resulting in surface water pooling and increased soil temperatures. Overall, the ET at forest sites seems to be strongly influenced by relative humidity while ET at tundra sites depends more strongly on air temperature.
Conclusion: Evaporation and transpiration are both important influences on soil moisture budget which tend to increase in young burns, but may be moderated by influences of soil structure, microtopography, and subsurface ice-melt.
New data compiled in NOAA’s 2024 Arctic Report card illuminates the delicate balance between boreal/arctic regions production of carbon dioxide (especially fire smoke and microbial respiration) and it’s uptake (by photosynthesizing vegetation). This balance is sensitive to ambient temperature, and of course is influenced in various ways by wildfire. Slowing down the atmospheric increase in CO2 from burning fossil fuels has taken on some urgency as we see more and more adverse impacts from warmer atmosphere and oceans due to its greenhouse effects. Land management and fire management may have a role to play, especially as we race to develop alternative energy sources. Take a look at this well-illustrated 8-p summary to bring yourself up to speed with what’s happening with carbon in the north country. Link to the report: https://doi.org/10.25923/0gpp-mn10
“When including wildfire emissions, the Arctic tundra region has shifted to a carbon dioxide (CO2) source and is a consistent methane (CH4) source.” (Natali et al. 2024, NOAA Technical Report OAR ARC ; 24-11)
Photo by R. Reanier: Anaktuvuk R Fire, July 14, 2007
A recent study headed by the University of Washington is catching national media attention currently as it points to a connection between exposure to wildfire smoke and dementia in older adults from a large study in California. One new advance is the ability to distinguish between ambient wildfire smoke vs. other types of fine particulate matter (PM2.5) exposure. Although the team’s publication in PubMed is pay-walled (Elser, et al. 2024), you can read a concise description of their work in this November, 2024 Research Highlight by the NIH National Institute on Aging, by Brian Doctrow, PhD. In a nutshell, among 1.2 million Californians aged 60+, there did seem to be a connection between neighborhood wildfire PM2.5 exposure and dementia diagnosis, which was considerably stronger than the connection with other types of fine particulate exposure. For every 1 μg/m3 increase in average wildfire PM2.5, the odds of receiving a dementia diagnosis increased by 18%.
Matsu engine protecting Nenana during the Parks Highway fire, 2006 (Photo: State of Alaska, DNR).
Download the latest Roundup with brief highlights of new publications that may interest the Alaska fire science and management community HERE. The fall Roundup includes links to articles on improvements in ranking fire risk around communities and structures, new findings on changes in fire regime in Alaska and Canada, implications of increases in high latitude fire on the atmosphere, and interesting findings on toxic components in fire retardant chemicals. Here’s the URL to a downloadable version:
Also, if you missed this webinar, be sure to check out the recorded presentation “Spark to Strategy“–by Rick Thoman (ACCAP) and Jake Dollard (Alaska Fire Service) on the 2024 fire season and how fire management plans turn into actions in Alaska.
Caribou lichens, Cladonia (Cladina) spp., are a slow-growing, vital winter forage for caribou. They are commonly called “reindeer moss” but aren’t really moss. And they are important to both reindeer and to caribou. Eric Palm (2022), for his PhD thesis, used GPS-collared caribou locations from several agencies in Alaska to show that caribou strongly avoided burned areas, especially in winter, and that their preference was related to lichen abundance. He concluded that: “caribou will experience increasing winter habitat loss as fire frequency and severity increase [in a warmer climate]. . . .We suggest that management strategies prioritizing protection of core winter range . . . would provide important climate-change refugia for caribou.” In a separate study, Matt Macander et al. (2020) demonstrated effective satellite mapping of lichen-rich ranges in Alaska, and his analyses also reinforced the caribou preference for habitat areas with >30% lichen cover.
Often you hear that lichens are only important in winter, but Libby Ehler (2021) used GPS video collars as well as diet analysis from droppings to show that lichens dominated caribou summer diet for the Alaska Fortymile Herd: 59% of composition of fecal pellets and 39% of observed foraging on the video collars in summer was lichen (vs. 37% shrubs). Only in June and July did the videos record a little more browsing on shrub than lichen, and in winter caribou expend a lot of energy locating and digging for rich patches of ground-hugging lichens. Previous studies demonstrated similar diet dominance by lichens in other herds in Alaska and Canada.
Now, in a new study, Liming He, of Natural Resources Canada, has documented large-scale decline in these lichen habitats in Eastern Canada. His study derived caribou lichen cover maps for two time periods ~30 years apart (1980’s, & 2020’s) using Landsat satellite imagery for a large area including several boreal caribou population ranges. Lichen cover declined in 62% of the region evaluated and increased in 11%. Fires were responsible for a quarter of the decrease, even in a region of Canada where fires have been relatively rare. The larger part (3/4) remains unexplained, with warming-induced shrub encroachment high on the list of suspects. Although we do not yet have a comparable study for Alaska, Macander et al. (2022) found lichen had declined 13% as a plant functional type in Alaska from 1985-2020, in a study that also used Landsat satellite data.
Taken together, these studies should alert wildlife and land managers about a possible habitat crisis on the horizon for Alaska’s 2nd largest subsistence resource. Indeed, most caribou herds across North America are experiencing declines, including the Western Arctic Caribou herd—once Alaska’s largest—featured in a recent Alaska Beacon article. The George River Caribou Herd in eastern Canada was the world’s largest in the 1990’s (800,000 animals) but by 2022 was down to just 7,200. Part of that herd’s decline is thought to be based on habitat degradation from overuse.
As one significant boreal research project (the NASA Arctic Boreal Variability Experiment) winds down, another important research collaboration is winding up, thanks to hard work by a group of scientists in Bonanza Creek Long-Term Ecological Research unit (BNZ-LTER). Both projects have tackled important fire science and management issues in Alaska. Although BNZ-LTER grew from the Bonanza Creek Experimental Forest (beginning in the 1980’s) and Caribou-Poker Creek Watershed, it’s work now expands across Alaska and western Canada and includes collaborating researchers from many locations, but especially University of Alaska and Northern Arizona University. BNZ-LTER also welcomes broad collaboration from land and resource managers and community stakeholders.
Research at the BNZ-LTER has always had a strong wildfire component.Dr Michelle Mack leads the unit as their Principal Investigator, as well as heading Northern Arizona University’s (NAU) Plant and Ecosystem Ecology Research Lab. In May 2023, Dr. Mack and her team were awarded a renewed grant of $7.6 m from the National Science Foundation for support through 2029. The project, titled Changing Disturbances, Ecological Legacies, and the Future of the Alaskan Boreal Forest, has several subtopics, including a Wildfire Working Group led by Dr. Xanthe Walker (NAU). The wildfire group is studying direct and indirect effects of fire, such as seedling re-establishment, effect on soil microbes, overwintered fires and stream chemistry. They are also studying fire management activities like fuel breaks. One recent publication by Walker, Mack, Johnstone, and others is highlighted in our latestResearch Brief: When does fire change a spruce forest into hardwoods?The paper discusses what has been learned from the LTER’s extensive network of post-fire forest plots on drivers and thresholds of stand-type conversions—a hot topic for a number of management applications.
Photo credit: Midnight Sun IHC ( Night burnout operation in L48).
Fuel treatments like thinning and fuel breaks often help trees better survive wildfires in the western US but their biggest direct benefit lies with providing operational choices and opportunities to firefighting teams. Presentations at the 10th International Fire Ecology & Management Congress this past month in Monterey outlined research on whether treating vegetation fuels before a fire threatens are “worth it”. Alan Taylor’s team looked at fuel treatments in the 2021 Dixie fire which burned over 1,500 square miles in 5 northern California counties (suppression cost $637,000,000 but losses estimated at $1.5 billion). Research found that previous fire–within the past decade–reduced the fire severity by a third (based on tree death and damage). There were some exceptions, where recent burns with heavy grass/brush cover got “nuked” in the re-burn under the extreme heat and drought conditions that prevailed that year. The biggest variables correlated with increased fire severity were forest biomass (using NDVI as a proxy) and tree cover. Variables associated with decreased severity included maximum relative humidity and fire operations. The latter is interesting, since burnouts and backfires are a major part of strategies to combat gobbler fires like Dixie. Taylor, a fire ecology professor at Penn State, estimated that these tactics used by firefighters reduced the area which would have burned with high severity by about 22%. It should be noted that burnout operations in western US conifer forests are often conducted at night whereas in Alaska they are more often daytime operations.
Another research effort led by Lacey Hankins studied the effect of previous fuel treatments on outcomes of the 2022 Washburn Fire in Yosemite National Park. They used fire effects plot data and Lidar data but also interviewed fire operations staff to find out if previous roadside thinning or other forest management treatment shaped tactics. Yosemite’s fuel treatments, conducted since the 1970’s, reduced forest density and fuel load—especially ladder fuels. Operations personnel felt previous prescribed fires and strategically placed fuel treatments were key considerations in tactics and helped them protect the town and the giant sequoias in Mariposa Grove. Other presenters in the session described moderation of fire severity in shaded (thinned) treatments up to 20 years old in forests of the Sierra Nevadas, while in southern British Columbia, thinning treatments only worked to lower crowning and torching in the more aggressive treatments. Low intensity thinning (400-1,400 stems/ha) treatments did not reduce modeled fire intensity, nor did pruning (Rutherford, 2023).
—Cited Presentations—
Alan H. Taylor, et al. (2023) The contributions of past fires and fire management operations to severity patterns of the Dixie Fire, Presentation at 10th Intl Fire Congress, Monterey, CA, Dec. 5-7, 2023.
Lacey E. Hankin, et al. (2023) Linking forest management to operational outcomes of the Washburn Fire in Yosemite National Park, Presentation at 10th Intl Fire Congress, Monterey, CA, Dec. 5-7, 2023.
Kea Rutherford, et al. (2023) Are operational fuel treatments successfully mitigating wildfire risk in British Columbia, Canada? Presentation at 10th Intl Fire Congress, Monterey, CA, Dec. 5-7, 2023.
AK Fire Science Highlights 