The most important ecological effects of fire may not be evident for many years after burning. Take permafrost, for example: just-published research is revealing extensive thawing and drying of soils in the aftermath of the Boundary Fire in interior Alaska. Brown et al. 2016 found almost all the severely burned plots in their study had thawed by 10 years after the 2004 fire. Without permafrost the burned areas were better drained, leading to drier soils, and influencing vegetation succession.
Typical burn appearance after 3 years (R. Jandt)
Another interesting facet of their study was the array of remotely-sensed data that Brown and colleagues employed, including optical and infrared spectra (Landsat 7 & 8), radar (L-band Synthetic Aperture Radar, or ALOS-PALSAR), and topographic (Light Detection and Ranging–LiDAR) datasets. Infrared indices used in the study were strongly correlated with soil moisture–allowing researchers to map the distribution of permafrost and compare it to burn severity maps.
How do you know whether forest fires or factories and diesel generators are responsible for Black Carbon or CO2 in the air or deposited in icefields? An experiment called CARVE (Carbon in Arctic Reservoirs Vulnerability Experiment) led by Chip Miller of the NASA Jet Propulsion Laboratory was conducted in Alaska’s airspace and some results just published explain how the source can be identified. The combustion of woody biomass (or more importantly in Alaska–layers of compacted dead moss and organic soil) liberates primarily carbon deposited since World War II into CO2. That modern post-bomb carbon contains traces of radioactive carbon (Δ14C) in contrast to fossil fuels, deposited in prehistoric times, which have none.
CARVE: Sherpa aircraft flew sensors over fires in Alaska in 2013 to measure atmospheric concentrations of gases.
During the CARVE experiment, Sherpa aircraft flew sensors to measure atmospheric concentrations of CH4, CO2, and CO and parameters that control gas emissions (i.e. soil moisture, freeze/thaw state, surface temperature). They directly flew over some fires (including fires near Fairbanks and Delta) to measure the “fingerprint” concentrations of isotopes released by typical boreal burning. Mouteva et al. (2015) published findings that showed most of the C in the summer skies over Alaska in 2013 was indeed attributable to forest fires and the age of the biomass converted to black carbon averaged about 20 years (range 11-47 yrs). The authors also explore using the carbon isotope “fingerprint” of fires to estimate the average depth of consumption–since Δ14C increases with depth from the surface moss to the mesic horizon. Pooled results of radioactive isotope fractions yielded an average depth of burn of about 8 inches for the 2013 Alaska fires–a result that may vary depending on fuel conditions. Burn severity, expressed as depth of consumption, is a hot topic among agencies and land managers because it drives ecological response to burning as well as vegetation changes which may come with the hypothesized climate-driven increased boreal burning.
Citation: Mouteva, G. O., et al. (2015), Black carbon aerosol dynamics and isotopic composition in Alaska linked with boreal fire emissions and depth of burn in organic soils, Global Biogeochem. Cycles: 29, doi:10.1002/2015GB005247.
A paper just published by the indefatigable Adam Young, a PhD candidate at the University of Idaho, and colleagues pulls together a lot of information about climate, forest, tundra and fire to offer a glimpse of potential future fire regimes in different parts of Alaska. By looking at fire occurrence at a multi-decadal time scale, the researchers drill down into how fire rotations are likely to respond to climate projections at a regional scale.
Exerpt from Fig. 6, Young et al. 2016. Figures in the paper not only show the observed fire rotation for 19 subregions of Alaska (Figure A2 in supplement) with 60 years of fire occurrence data, but also project future rotations under various climate scenarios (in this case a mean of of 5 global climate models).
The use of advanced statistical models to build fire-landscape response models for boreal forest and tundra reaffirms prior findings of the sensitivity of fire regime to summer temperatures and moisture deficit. However, the effect is not uniform among regions: they identify a threshold at about 56⁰ F (30-yr mean temperature of the warmest month) and another threshold for annual precipitation where fire occurrence really seems to jump. This latter finding accounts for results which project large increases in 30-year probability of burning for areas where these thresholds will be crossed in the next several decades. For example, models project the Brooks Range foothills of the North Slope, Noatak tundra and the Y-K Delta may see increases in fire 4-20x greater than historical levels. Some tundra areas are likely to experience fire frequency increase to levels not observed in the paleo record, spanning the past 6,000-35,000 years. Across most of the boreal forest, fire rotation periods are projected to be less than 100 years by end of the 21st century. This is useful information for natural resources management as well as fire protection agencies—a concise, well-researched, well-illustrated paper—put it on your summer reading list.
Young, A. M., Higuera, P. E., Duffy, P. A. and Hu, F. S. (2016), Climatic thresholds shape northern high-latitude fire regimes and imply vulnerability to future climate change. Ecography 39: 1-12. http://dx.doi.org/10.1111/ecog.02205
It has long been assumed that bark beetle outbreaks on the Kenai lead to increased fire danger, even though beetle disturbance has been shown to have mixed effects on crown fire potential, fuel profiles and burn severity in the Rocky Mountains. Winslow Hansen, doctoral candidate at the University of Wisconsin, recently published an analysis of beetle outbreaks and fire on the Kenai Peninsula between 2001-2014 (Hansen et al. 2016). He looked at effects in pure white spruce stands–where duration of beetle attacks is longer and mortality greater–and in mixed white and black spruce stands common on the northern peninsula, where attacks are less severe. His analysis indicates mixed effects: severely damaged white spruce stands did not demonstrate increased fire occurrence (instead, % canopy cover appeared to drive likelihood of burning) while the mixed white/black spruce stands didshow a positive correlation with beetle outbreaks and fire. Winston explores the reasons for this in his relatively short article: worth reading. You may remember Winslow from his previous work on beetles/fire effects and property values on the Kenai (recorded MS Thesis defense) and climate effects on fire regime (recorded 2015 presentation).
Estimates of carbon released from combustion of vegetation and organic soil during wildfires have improved dramatically over the past decade. Biomass inventory, fire effects and fire severity studies have contributed more accurate data to improve these models. (See Ottmar 2007, Brendan Rogers webinar 2015) However, figuring out the net effect of all the various effects of fire, the recovery phase and warming climate on the carbon stored in Alaska’s forests and tundra is a lot more challenging! You’d have to consider changes in burn extent and/or severity, increases in plant productivity in recovering burns, changes in species composition and what that means for productivity, changes in permafrost distribution and soil C decomposition, methane emissions and carbon fluxes in lake systems and wetlands–etc.! A team lead by Dr. Dave McGuire at UAF has taken on this modeling challenge by applying their Integrated Ecosystem Model (IEM) which includes modules for fire, permafrost, and carbon cycling. Dave recently presented an overview of their findings at an IARPC-WCT/AFSC joint webinar (presentation slides available HERE). In a nutshell, they found: 1) tundra holds 2x the carbon that boreal forest does in the same area 2) there has been a net C loss from boreal land area of about 8 Tg/yr over the last 60 years, primarily driven by large fires during the 2000’s 3) arctic tundra and SE Alaska still act as C sinks, compensating for these losses so that overall, Alaska sequesters about 3.7 Tg/yr, 4) increases in fire extent predicted with with warming climate will release even more C, but longer growing seasons and increased plant growth (as much as 8-19% increased productivity throughout the remainder of this century) with warmer climate and higher CO2 concentration in the atmosphere are estimated to offset these losses under most of the climate projection scenarios. Since this nutshell summary glosses over a lot, you should take a look at the slides and the SNAP projects page with information on scenarios and the individual models used.
A new report by USFWS Kenai Refuge fire staff (Nate Perrine) examines
areas where the 2015 Card Street fire intersected completed fuels treatments. He utilized IFTDSS (Interagency Fuels Treatment Decision Support System) modeling to analyze the treatment effect on fire behavior, and also documented post fire effects within the treated areas. This well-illustrated discussion includes recommendations for future treatments and analyses–a must-read for fire fuels specialists in Alaska! Click below to download a pdf.
The first 2016 issue of Western Forester contains a pair of short articles on the Nenana Ridge crown fire experiment and fuel break effectiveness at Funny River and the studies in progress on fuel break effectiveness in Alaska. Eric Miller (BLM-Alaska Fire Service) and Nathan Lowjewski (Chugachmiut Forester) did a nice job on these write-ups! Eric’s article gives the first published account of what happened in 2016 when wildfire challenged a 10-year old thinned fuel break in black spruce, as well as insight to the “hows” and “whys” of fire behavior in fuel breaks. Here’s a link to the issue: http://www.forestry.org/media/docs/westernforester/2016/WFJanFeb2016-2_LT3qttf.pdf
The Yukon Hot Shot Crew puts finishing touches on experimentally thinned fuel treatment blocks in June, 2007 (R.Jandt).
You might be surprised by the amount of collaboration between Alaska and Michigan-based scientists over the last 2 decades! This has been a long-standing research relationship which has spawned many useful products–including Alaska’s fire perimeter map database! Other endeavors include satellite fire detection and mapping, fuel moisture detection, improvements in fuels mapping, tundra fire research and more. Read about the history of this research relationship and its important findings and products, still ongoing with some exciting current research endeavors in a new Research Brief (LINK).
NASA’s Arctic Boreal Vulnerability Study (ABoVE) has focused a research spotlight on Alaska & Canada this year. In August, 2015, they announced 21 new projects funded for a multi-year field campaign designed to investigate the ecological and social impacts of changing permafrost, wildfires, and wildlife habitats in Alaska and northwestern Canada. Many of these involve new approaches to use remote sensing information from satellites. At least 5 funded projects involve field work in Alaska and direct involvement with the wildfire science and/or management in Alaska. Read about the new ABoVE projects at: