Inlernational Journal of Wildland Fire, 2001,
10,405-4! 3
Fire, climate change, carbon and fuel management
in the Canadian boreal forest
B.D. AmiroAC, B.J. StocksB, M.E. Alexander'\ M.D.
A
FlanniganA and B.M. Wotton
Canadian Forest S�ryicc, Northern Forestry Centre, 5320-122 St, Edmonton, AB, T6H3S5, Can,
BCanadian Forest Service, Great Lakes Forestry Centre, 1219 Queen St. E., Sault Ste. Marie,
ON, P6A5M7, Canada.
cTelcphonc: +1 780435 7217; email: [email protected]
This paper was presented aI the conferellce 'Integrating spatial technologies and ecological principles
for a new age infire management', Boise, Idaho,
USA, JUlie J 999
Abstract. Fire is the dominant stand-renewing disturbance through much of the Canadian boreal forest, with large
high-intensity crown fires being common. From 1 to 3 million ha have burned on average during the past 80 years,
with 6 years in the past two decades experiencing more than 4 million ha burned. A large-fire database that maps
forest fires greater than 200 ha in area in Canada is being developed to catalogue historical fires. HOWL"Vcr, analyses
using a regional climate model suggest that a changing climate caused by increasing greenhouse gases may alter
fire weather, contributing to an increased area burned in the future. Direct carbon emissions from fire (combustion)
are estimated to average 27 Tgcarbon year-! for 1959-1999 in Canada. Post-fire decomposition may be of a similar
magnitude, and the regenerating forest has a different carbon sink strength. Measurements indicate that there is a
net carbon release (source) by the forest immediately after the fire before vegetation is re-estflblished. Daytime
downw.ml carbon fluxes over a burned forest lake 1-3 decades to recover to those of a mature forest, but the annual
carbon balance has not yet been measured. There is a potential positive feedback to global climate change, with
anthropogcnie greenhouse gases stimulating fire activity through weather changes, with fire releasing more carbon
while the regenerating forest is a smaller carbon sink. However, changes in fue! type need to be considered in this
scenario since fire spreads more slowly tnrough younger deciduous forests. Proactive fuel management is evaluated
as a potential mechanism to reduce area burned. However, it is difficult to envisage that such treatments could be
employed successfully at the national scale, at least over the next few decades, because of the large scale of
treatments required and ecological issues related to forest fragmentation and biodiversity.
Keywords:
forest fire, climate change, fuel management, boreal forest, carbon.
Introduction
The circumpolar boreal forest covers 1.4 billion ha, with
about 340 million ha in Canada. Between 5000 and 12 000
forest fires burn annually in Canada, covering 1-3 million
ha, although �here have been 6 years since 1980 where morc
than 4 million ha have burned (Fig. I). Although there is
much inter-annual variability, it is apparent that area burned
has increased in the last part of this century. HowL'Ver, the
older statistics are more uncertain, and likely underestimate
fire occurrence and size prior to 1970. In Fig. 1, we have also
plotted lines representing 75- and J OO·year fire cycles, based
on a total foresr area for Canada of 418 million ha (CCFM
1997). A fire cycle of this magnitude is in the range of that
expected for the boreal forest based on studies of smaller
areas across Canada (e.g. Bergeron 1991; Ward and Tithecott
1993; Larsen and Macdonald \998). These relative baselines
show that fire cycles lire still relatively long at the national
level, even in recenl years where more area has burned. The
mean fire cycle for the whole forested part of the country for
the 1980 -1999 period is 155 years. However, the fire cycle
would be 126 years bascd only on the boreal (including taiga)
area of 341 million ha (CCFM 1997) where Ihe majority of
fires occur. This laner period reflects the current regime
using our most confident data. If the data between 1920 and
1980 are not underestimates, then it is likely thaI fire cycles
were abnormally long during this period.
10. i07lfWFOlOJR
1049-800 t/O IfOJ040S
406
RD. Amiro
8,-------,
Annual Area Burned In Canada
1920�1999
o
1920
1940
1960
1980
2000
Year
Fig. l.
Annual forest area burned in Canada 1920-1999. 11le
horizontal dashed lines show the area that would be burned if fire
cycles ranged between 7S and 100 years.
Fig. 2.
ef al.
A large-fire database is being developed for Canada,
where all forest fires greater than 200 ha in area are explicitly
mapped in a Geographical Information System (GIS). These
larger fires are most important since only 2-3% of the fires
account for 97-98% of the area burned, at least during the
1970-1985 period (Stocks 1991). This database includes
spatial polygons of each fire, with supporting information on
the month that the fire started, area burned, suppression
actions, and cause of ignition. In some cases, large unburned
islands are also mapped. The database is a compilation from
individual provinces and territories, as well as national
park lands, but includes only designated forest areas
(i.e. rangelands are excluded). Th.e database is reasonably
complete for the 1959-1999 pcriod, and cfforts are being
made to acquire more data prior to 1959. In most cases, fires
were mapped usn
i g aerial photographs and ground surveys,
but more recent techniques usc global positioning system
mapping from aircraft and satellite imagery in remote areas
during busy fire seasons. A map of these large fires for a 15year period clearly shows that fire has a large impact on the
landscape (Fig 2).
Large-fire database. Fires ofarea greater than 200 h3 are plotted for the period 1980--1994. The black polygons are actual fife sizes and
locations. The box outlined in the diagram (arrow pointing) is the approximate location of the enlarged area described in Fig. 6.
Fire, climate (;lIange, (;arbon and fuel management
409
We have been gathering some data on post-fire carbon
that anthropogenic emissions are increasing atmospheric
losses in Sl,lpport of the modeling efforts. for example,
carbon dioxide concentrations,
carbon dioxide flux was measurcd using the eddy-covariance
occurrence, which in turn releases more carbon to the
technique from an aircmft during the BOREAS experiment
atmosphere while reducing the forest as a sink:. The next few
in northern Saskatchewan and Manitoba in 1994 and 1996
(Amiro
e( af. 1999). Data were collected over burns of
different ages, and the relative flux ncar midday was
compared (Fig. 5). We
see that
carbon
dioxide
flux
which can increase fire
decades will show whether such a feedback is significant.
Mitigation: Fuel management ovcr large areas
The preceding discussion indicates that fire is currently a
(downward) is reduced to about 25% of that in more mature
major disturbance on thc boreal forest, that it is likely to
areas I year after the fire, and that this slowly increases with
increase with a changing climate, and that it has strong
30 years.
influence on the foresl carbon balance. Most of the boreal
However, fluxes measured during recent burns (i.e. the same
time since fire, finally recovering at about
forest is ecologically adapted to fire, and we believe that fire
These
is an important and necessary feature to maintain ecological
measurements implicitly included a range of stands along a
integrity. However, in addition to the global carbon issue, fire
year)
were
500-1cm
upward,
trdllseet
indicating
and,
net
although
respiration.
they
show
day-time
is seen to compete with harvesting of forest resources, and
photosynthetic sinks, night-time data are absent. Short (1-2
especially with fiber production, such that policies for
week) field campaigns measuring carbon fluxes using cddy
controlling unwanted
covariance continuously from towers over burned jackpine
Canadian boreal forest. Given that Canada spends about
forests show respiration only over a I-year-old bum, but a
SUS350 million annually on fire suppression, there is a
IO-year-old burn
question whether Fuel management could help reduce fire
has fluxes that approximate those of a
nearby malure site (Amiro 2001). A combination of remote
fires still dominate much of the
suppression costs.
sensing dara and a mOOel of net primary productivity (NPP)
We first make an assumption that fuel management can be
shows an almost linear increase ofNPP with time since fire,
successfully used to protect relatively small areas of valued
with a slope that varies among Canadian ccoregions (Amiro
resources
and
communities.
Although
there
are
few
et of. 2000). In at least some areas, l\rpp does not reach that
quantitative examples of
of a mature forest until 2-3 decades following firc. These
practice, we believe that sufficient effort can be applied at
whether this
can
be done in
studies show that fire reduces net carbon fluxes (i.e. reduces
small scales to limit fire spread. However, at the national
the forest sink strength) at least Oil the scale of years to
scale, the qucstion is whether proactive fuel management can
decades and is even a carbon source to the atmosphere
docrease or limit area burned if severe or critical fire weather
immediately after the fire. The potential positive feedback is
occurs more regularly in a changing climate.
Using our large-fire database, we can look more closely
at some of the fire features in an area where there has been a
large fraction of the area burned during recent years. We
selected all area of about 400 x 400 Ion (16 million ha) in the
1.0
boreal shield ecozone of northern Saskatchewan (square
:g
•
0
0
t
0.6
g
•
>
"
•
..
,;
�
•
•
0.6
outlined
area is coniferous with a smaller �eciduous component.
stands of deciduous (aspen, balsam poplar) or coniferous
•
(spruce, pine) mixed in with other geneml fuel lypes. Figure
0.'
6 shows fire areas grouped into 3-5 year intervals as colored
polygons. In addition, the 1995 polygons are ploued as
•
<
•
U
Fig. 2). The fuel types (defined by AVHRR
However, there is more variabi Iity at smaller scales, with
;
�
in
satellite data with about I km2 pixels) show that most of the
0.2
0.0
transparent outlines. The polygons generally fit together like
puzzle parts with new fires interlocking with previous burns.
Very little orthe area is rcburned during h
t is period, as shown
C--+--_-_-_-_-_--<
o
,
'"
"
"
Age of burn (years)
"
by the 1995 polygons where fires in the western and north­
"
central parts of the figure follow the contours around
previous burns. The influence of major fuel type differences
Daytime (;arbon flux (downward) measurements lIsing eddy
l:Ovanan(;e from aircraft over burned areas dudng the 1994 and1996
Fig. 5.
BOREAS experiment
(Arniro eJ al.
expressed as a fra(;tion of a
among flights.
1999). The carbon flux
mature forest.
s
i
The error hlml are ± I S.E.
and natural barriers to fire spread can also be seen. Only the
very large lakes act as fire breaks and there are cases where
the fire polygons appear to avoid large deciduous areas, as
shown by a 1995 fire in the south-cast eomcr of the figure.
This illustrdtes that essentially only very large lakes, recent
Fire, ciilllllte change, carbon and fuci management
'II
""
Boreal Spruc9
'"
00
"
E
.
E
�
"
•
•
00
..
00
•
�
�
Boreal Mi,,,,tMJoO(!
(50%ooni!<l1)
•
..
•
•
u:
•
•
•
,
'"
(50% ooni!or)
·S<lmmer
'"
"
"
0
"
0
Inllial Spread Index (lSI)
Fig. 7.
Head fire mte of spread on level terrain as a fUlleliou orlhe Initial Spread
Index (ISO of the Canadian Forest Fire Weather Index (FWIJ System (after Forestry
Canada 1992)_ The lSI component of the FWI System is
a
reJotive numerical r::Jting
of the expected rate of fire spread tltat 13kes into account the eff�ts of fille fuel
moisture content based on past and current weather conditions. A crown fire would
occur in spruce at lSI > 9 and mixed wood stands in summer at lSI> 21.
the decrease in rate of spread that can
be achieved by altering
the fuel types from pure spruce to a mixedwood forest (50%
conifer, 50% deciduous) to a pure deciduous stand in the
cured in spring and fall, the fire rate-of-spread can be much
greater than it would be in nearby mature forests (see Fig.
7).
Our third management option involves fuel isolation,
spring prior to leaf-out (leafed deciduous stands have even
In many areas, this shift in fuel type
whereby patches of fuel are separated on the landscape to
lower rates of spread).
restrict fire spread. [n an area of uniform fuel type with equal
may nol be easy to achieve since there are only a limited
chance of the fire starting and spreading, we could envisage
number of species available. For example, in the western part
a management plan where fuel breaks are inserted on the
of the boreal forest, essentially aspen and balsam poplar are
landscape in some pallcrn that strategically makes use of
the only commercial tree species available to replace the
existing fuel breaks and natural barriers such as large lakes.
spmces, and often there is no other large tree species that can
These fuel breaks may be efe
f etivc in stopping fires by
replace black spmce in Low�lying parts of the landscape.
Even if such
a
species shift could be managed, there
would be large ecological changes to the landscape and
themselves, may slow fire growth to allow suppression, or
may provide anchor points for suppression
activities.
Therefore, they could be totally devoid of fuel (e.g. a fire
has a
severe concerns about biodiversity. Further, a species shift
break such as bare soil) or contain a fuel type which
would have economic impacts that would need to be
slower fire spread potential (e.g. aspen). In any case, for the
fuel conversions arc occurring
present analysis, we will assume that these fuel breaks are
through both human�caused and natural disturbances, as well
considered.
Of course,
perfect, and will restrict fire spread. The question is whether
as successional trends, and some of the inadvertent changes
such a fuel isolation scheme can limit fire size to decrease
affect fire behavior. An example is the encroachment of a
area burned at the national landscape level. Based on pure
grass, Calamagrostis canadensis, in western boreal regions
geometry, we can test for the scale of treatment required to
after harvesting (Lieffcrs el a/. 1993): when this grdSs is
protect an area using a simple square grid. We recognize that
412
B.D. Amiro etai.
"TT-------,
�
��\
•
1997),
and many of
the more intense fires could easily jump a 200·m fuel break.
"D
�
breaks. For comparison, about I million ha per year arc
har vested in Canada currently (CCFM
perhaps as often as every few years. So for large areas, a
,�
large investment would be needed with questionable results.
Further, large·scale fragmentation of the boreal forest by fuel
•
•
.0
o
Also, these fuel breaks would require some maintenance,
\
:\
.�
•
O�
\
'-,,--
300m
�:-:-:
•
breaks would nol be acceptable ecologically, irrespective of
-._
-'-"-
'-::-.":':': :-:-:-.�.7':": :-:-:-.�.� -=-=.!j
..
-
other ecological issues related to reducing fire.
These reasoned arguments suggest that proactive fuel
management will not be very successful to reduce
area
burned in Canada as a whole, at least over the next few
decades. Over longer time scales, settlement and land·use
limit of si n g le fire area (ha)
patterns may change, and it is difficult to make predictions
over centuries. However, some of these fuel management
Geometries of a proactive fuel [wlatlon treatment. The lines
schemes may be useful to protect valued areas over smaller
treated to provide a fucl break of a given width (100 m, 200 m, 300 m,
fuc! discontinuity is already present, such as in areas with
Fig. 8.
arc curves of the percentage of the landscape area that needs to be
1000 m), such that the maximum fire size is limited to that shown on
the x-axis.
This assumes that the fuel isolation rreatmcnls are in a
square grid paucrn, and act as perfect fuel breaks.
scales. This would be most easily implemented where some
larger deciduous componenl'> or where many recent fires
provide some natural barriers to fire spread.
Conclusions
Fire is the dominant stand-renewing agent in inost of the
a fuel break management plan would use existing landscape
Canadian boreal forest: eeologicaHy, this forest needs fire. A
features that are not square, but alternative geometries do not
changing climate in an atmosphere with enhanced CO2
change the scale very much (they tend to increase the length
concentrations is likely [0 atlect both fire weather and
However, the feedbacks have not
of the fuel break, but this is partially compensated by
vegetation (file!) types.
existing natural breaks).
been estimated, so that it is difficult to predict whether
Figure 8 shows the percentage of an area that must be
interactions between weather, fuels, land-use practices, fire
treated to form a fuel break that will limit single fires to a
history, and fire·exclusion practices will change fire regimes
given area. We have shown four widths of fuel breaks, with
drastically. For example, if more fire creates a younger
increasing break width corresponding to protection for
successional deciduous forest, then fire spread may be
increasingly vigorous flre behavior. A wide break of
I kIn (or
perhaps more) is
. required to restrict spotting in extreme
limited until successiop to conifers occurs. The impact of
fire on the carbon balance is being studied, bul we still need
cases, but it may be more practicable to use this fuel isolation
to get better estimates of post-fire carbon losses through a
scheme onLy for less intense fires, where fuel breaks on the
combination of fleld measurements and modeling. We
order of 100 m are effective. The curves show that, if fires
believe
arc to be limited to sizes of less than 1000 ha, lhen a
management is unlikely to be successful in decreasing area
relatively large percentage of the total area needs to be
burned in Canada ill the near future. This is because of the
included as a fuel break area. However, the curves become
large
flattcr at grcater areas. For example, if a manager decided
that a fuel break of200 m width would be adequate to isolate
that,
area
on
the
national
scale,
proactive
fuel
that would need to be treated. However, fuel
management does have a role in protection of forests,
including eonununities and other valued resources, but at
fuels for a given fire behavior situation, then about 4.5% of
small scales. Although the boreal landscape is becoming
the area would need to be included as the fuel break to
increasingly fragmented because of human activities, this
restrict each fire to less than 2000 ha. For small management
has had litHe impact on the growth of h
t e larger fires, which
areas of the range of 100 000 ha, this would mean
contribute much of the area burned.
thai 4500
ha would need to be treated. Such a scheme may be possible
by incorporating a range of mechanicaJ, prescribed fire, and
chemical options, although there would be some periodic
maintenance required.
Acknowledgements
The authors thank the large number of individuals who
contributed to data compilation for the Canadian large·fire
Hov.'Cvcr, at the national scale, it is difficult to imagine
database in the provincial and territorial agencies, Parks
that all of the 341 million ha of the Canadian boreal forest
Canada, and the Canadian Forest Service. The senior author
could be included to reduce area burned. TillS would require
thanks Ihe Joint Fire Science Conference for financial
15 million h a be treated for a scheme with 200·m·wide fuel
support to attend the conference.
413
Fire. climate change, carbon and fuel management
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