Alaska’s changing fire regime — implications for
the vulnerability of its boreal forests1
Eric S. Kasischke, David L. Verbyla, T. Scott Rupp, A. David McGuire,
Karen A. Murphy, Randi Jandt, Jennifer L. Barnes, Elizabeth E. Hoy, Paul A. Duffy,
Monika Calef, and Merritt R. Turetsky
Abstract: A synthesis was carried out to examine Alaska’s boreal forest fire regime. During the 2000s, an average of
767 000 hayear–1 burned, 50% higher than in any previous decade since the 1940s. Over the past 60 years, there was a de-
crease in the number of lightning-ignited fires, an increase in extreme lightning-ignited fire events, an increase in human-
ignited fires, and a decrease in the number of extreme human-ignited fire events. The fraction of area burned from human-
ignited fires fell from 26% for the 1950s and 1960s to 5% for the 1990s and 2000s, a result from the change in fire policy
that gave the highest suppression priorities to fire events that occurred near human settlements. The amount of area burned
during late-season fires increased over the past two decades. Deeper burning of surface organic layers in black spruce
(Picea mariana (Mill.) BSP) forests occurred during late-growing-season fires and on more well-drained sites. These
trends all point to black spruce forests becoming increasingly vulnerable to the combined changes of key characteristics of
Alaska’s fire regime, except on poorly drained sites, which are resistant to deep burning. The implications of these fire re-
gime changes to the vulnerability and resilience of Alaska’s boreal forests and land and fire management are discussed.
Re´sume´ : Une synthe`se a e´te´ effectue´e pour e´tudier le re´gime des feux de la foreˆt bore´ale en Alaska. Durant les anne´es
2000, le feu a de´truit en moyenne 767 000 haan–1, soit une superficie 50 % plus grande qu’au cours de n’importe quelle
de´cennie pre´ce´dente depuis les anne´es 1940. Au cours des 60 dernie`res anne´es, le nombre de feux de foudre a diminue´,
les feux de foudre majeurs ont augmente´, les feux d’origine humaine ont augmente´ et le nombre de feux majeurs d’origine
humaine a diminue´. La proportion de la superficie bruˆle´e par des feux d’origine humaine a chute´ de 26 % au cours des an-
ne´es 1950 et 1960 a` 5 % au cours des anne´es 1990 et 2000 a` cause d’un changement de politique de gestion du feu qui ac-
cordait la plus haute priorite´ a` la suppression des feux qui surviennent pre`s des e´tablissements humains. La superficie
bruˆle´e par les feux de fin de saison a augmente´ au cours des deux dernie`res de´cennies. Les horizons organiques de surface
ont e´te´ bruˆle´s plus en profondeur dans les foreˆts d’e´pinette noire (Picea mariana (Mill.) BSP) par les feux de fin de saison
et sur les stations les mieux draine´es. Toutes ces tendances contribuent a` rendre les foreˆts d’e´pinette noire plus vulne´rables
aux changements combine´s des caracte´ristiques cle´s du re´gime des feux en Alaska, a` l’exception des stations mal draine´es
qui sont re´sistantes aux feux de profondeur. La discussion porte sur les conse´quences de ces changements des caracte´risti-
ques du re´gime des feux sur la vulne´rabilite´ et la re´silience des foreˆts bore´ales de l’Alaska et sur la gestion des feux de fo-
reˆt.
[Traduit par la Re´daction]
Introduction
Wildland fire is one of the most widespread and important
disturbances affecting Alaska’s boreal forests. Its role in reg-
ulating ecosystem processes across the North American bor-
eal forest has long been recognized (Viereck 1973; Wein
and MacLean 1983). Since 2000, research carried out by
the Bonanza Creek LTER program and projects funded by
other agencies have focused on developing a clearer under-
standing of how variations in the fire regime impact forest
Received 26 August 2009. Accepted 16 February 2010. Published on the NRC Research Press Web site at cjfr.nrc.ca on 28 June 2010.
E.S. Kasischke2 and E.E. Hoy. Department of Geography, 2181 LeFrak Hall, University of Maryland, College Park, MD 20742, USA.
D.L. Verbyla, T.S. Rupp, and P.A. Duffy. Department of Forest Sciences, School of Natural Resources and Agricultural Sciences,
University of Alaska Fairbanks, Fairbanks, AK 99775-7200, USA.
A.D. McGuire. US Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks,
AK 99775, USA.
K.A. Murphy. National Wildlife Refuge System, Anchorage, AK 99503, USA.
R. Jandt. Alaska Fire Service, Bureau of Land Management, Fort Wainwright, AK 99703, USA.
J.L. Barnes. US National Park Service, Fairbanks, Alaska 99709, USA.
M. Calef. Department of Geography and Planning, SUNY Albany, Albany, NY 12222, USA.
M.R. Turetsky. Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
1This article is one of a selection of papers from The Dynamics of Change in Alaska’s Boreal Forests: Resilience and Vulnerability in
Response to Climate Warming.
2Corresponding author (e-mail: ekasisch@umd.edu).
1313
Can. J. For. Res. 40: 1313–1324 (2010) doi:10.1139/X10-098 Published by NRC Research Press

ecosystems and the services they provide (Euskirchen et al.
2010; Johnstone et al. 2010; Jorgenson et al. 2010; Kofinas
et al. 2010; Turetsky et al. 2010).
Alaska’s fire regime is not only regulated by regional cli-
mate and landscape variations in physiography and ecosys-
tem structure but also by human ignitions, regional fire and
land management suppression policies, and local community
actions (Fig. 1). What remains unclear is whether the net ef-
fect of these interactions will tend to maintain a constant
level of fire activity in the face of global climate change or
whether shifts in characteristics of the fire regime will oc-
cur. If there are no responses, then the fire regime is resil-
ient to climate change; however, if there are, then the fire
regime is vulnerable to climate change and the challenge be-
comes identifying which characteristics are likely to influ-
ence the vulnerability of forest ecosystems and the services
they provide.
For this paper, we reviewed our current understanding of
Alaska’s fire regime based on new insights derived from re-
search conducted since a previous synthesis that was based
on data through the 2000 fire season (Kasischke et al.
2006). There were four areas that provided for an extension
of this previous synthesis effort. First, there were four large
fire years during the 2000s that burned some 6.6  106 ha
(or 15% of the boreal forest region of interior Alaska below
treeline) and their occurrence has changed many of the met-
rics used to quantify the fire regime. Second, more detailed
information on fire events from the 1950s and data on light-
ning strikes have recently become available through efforts
of the Alaska Fire Service to update their databases. Third,
a number of field-based studies that quantified fire severity
have recently taken place. And fourth, the development of
fire information products from satellite remote sensing data
has created new tools for the study of spatial characteristics
of the fire regime.
This paper is based on a review of the scientific literature
as well as new data analyses. The methods used in these ad-
ditional analyses are summarized in online supplemental
materials3, and the information from them is presented in
Tables 1 and 2 and Figs. 2–6. For the synthesis, we further
examined the longer-term patterns of burned area in Alaska
(1860–2009), reviewed a number of fire regime characteris-
tics and factors influencing fire during the modern era
(1950–2009), and assessed information generated through
analysis of satellite remote sensing data. We evaluated the
possible causes for variations in burned area over the past
70 years, focusing on the relative roles of changes in climate
versus changes in fire management policies. We then as-
sessed the implications of the changing fire regime in
Alaska, both in terms of vulnerability and resilience of Alas-
ka’s boreal forest and in terms of ecosystem services and
fire management options, and identified priorities for future
research.
Longer-term trends in burned area
Combining burned area derived from climate reconstruc-
tions (1860–1939) with estimates from fire management re-
cords (1940–2009) provided for an assessment of longer-
term trends in Alaskan wildfire activity (Fig. 2). Average
area burned at a decadal scale was regulated by the fre-
quency of large fire years (>470 000 ha burned), which rep-
resented 17% of all years and accounted for 68% of burned
area. There was a change in Alaska’s fire regime beginning
early in the 20th century. Since the 1920s, there has been at
least one large fire year each decade, an average of 2.3 large
fire years per decade, and an average area burned of
399 700 hayear–1. The highest average annual burned area
(767 000 hayear–1) occurred in the 2000s. Between 1860
and 1919, there were three decades without a large fire
year, an average of 0.8 large fire years per decade, and an
average burned area of 420 400 hayear–1. The highest aver-
age burned area of 264 900 hayear–1 occurred during the
1870s. The fire return interval was 159 years for 1860–1919
and 105 years for 1920–2009.
Data from the 1940s to 2000s show that the number of
large fire years during the 1940s and 1950s was the same
as during the 1990s and 2000s (seven), with less frequent
large fire years during the intervening 30 years (4)
(Fig. 3). The number of extreme fire events (>50 000 ha)
was high during the 1950s, low in the 1960s through
1980s, and then rose during the 1990s and 2000s (Table 1).
As a result of changes in the frequency of large fire years
and extreme fire events, there was a decrease in decadal
average area burned from the 1940s and 1950s through
the 1980s and a rise in the 1990s and 2000s. The 2000s
experienced the highest burned area and number of ex-
treme fire events during the modern record period (Table 1;
Fig. 3).
The relationship between burned area and the number
of large fire years has been observed across all Canadian
boreal forest ecoregions (Kasischke and Turetsky 2006).
The burned area trend in Alaska over the past 70 years
differs from that observed Canada, where average
burned area increased continuously from the 1940s
(816 500 hayear–1) through the 1990s (3 170 700 hayear–1)
(Gillett et al. 2004) before sharply descreasing in the 2000s
(1 654 300 hayear–1).
Fig. 1. Conceptual model of the interactions among climate, eco-
systems, fire, human communities, and fire policy in the Alaskan
boreal forest (modified from Chapin et al. 2003, 2008).
3 Supplementary material for this article is available on the journal Web site (http://cjfr.nrc.ca).
1314 Can. J. For. Res. Vol. 40, 2010
Published by NRC Research Press