• boreal forest;
  • climate;
  • charcoal;
  • fire frequency;
  • Holocene;
  • laminated sediments;
  • pollen;
  • Quebec


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References
  • 1
    Studies on the variability of natural fire regimes are needed to understand plant responses in a changing environment. Since vegetation changes might follow or trigger changes in fire frequency, climate models suggest that changes in water balance will accompany current global warming, and the response of fire regimes to Holocene hydro-climate changes and vegetation switches may thus serve as a useful analogue for current change.
  • 2
    We present high-resolution charcoal records from laminated cores from three small kettle lakes located in mixed-boreal and coniferous-boreal forest. Comparison with some pollen diagrams from the lakes is used to evaluate the role of the local vegetation in the fire history. Fire frequency was reconstructed by measuring the separation of peaks after detrending the charcoal accumulation rate from any background.
  • 3
    Several distinct periods of fire regime were detected with fire intervals. Between c. 7000–3000 cal. year BP, fire intervals were double those in the last 2000 years. Fire frequency changed 1000 years earlier in the coniferous-boreal forest than in the mixed-boreal forest to the south. The absence of changes in combustibility species in the pollen data that could explain the fire frequency transition suggests that the vegetation does not control the long-term fire regime in the boreal forest.
  • 4
    Climate appears to be the main process triggering fire. The increased frequency may be the result of more frequent drought due to the increasing influence of cool dry westerly Pacific air-masses from mid to late Holocene, and thus of conditions conducive to ignition and fire spread. In east Canada, this change matches other long-term climate proxies and suggests that a switch in atmospheric circulation 2–3000 years ago triggered a less stable climate with more dry summers. Future warming is moreover likely to reduce fire frequency.


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References

Fire is the main natural disturbance in the North American boreal forest (Rowe & Scotter 1973). Sustainable forest harvesting could mimic the effects of current natural fire regimes (Delong & Tanner 1996), because effects of natural fire are similar to those of industrial forest harvesting (Johnson et al. 1998). There is, however, little doubt that the current and predicted global warming could cause changes in forest disturbances. While some studies in northern America anticipate an increase in fire frequency (Clark 1988; Stocks et al. 1998) or size of burns (Flannigan & Van Wagner 1991; Wotton & Flannigan 1993), others suggest a decrease (Bergeron & Flannigan 1995; Bergeron et al. 2001). Simulations based on mathematical models predict that the Canadian Fire Weather Index (CFWI) will increase in central and eastern North America but will be lower in the north-east (Flannigan et al. 1998, 2001). Understanding the long-term relationships between climate and fire regimes is thus essential for the sustainable management of the boreal forest in a changing climatic environment (Bergeron et al. 1998).

Dendroecological studies show that both frequency and size of fire decreased during the 20th century in both west (e.g. Van Wagner 1978; Johnson et al. 1990; Larsen 1997; Weir et al. 2000) and east Canadian coniferous forests (e.g. Cwynar 1977; Foster 1983; Bergeron 1991; Bergeron et al. 2001), possibly due to a drop in drought frequency and an increase in long-term annual precipitation (Bergeron & Archambault 1993). From a longer-term perspective, high-resolution studies of fire regime are necessary to decipher the relationship between climate and fire. Unfortunately, no high-resolution data covering the entire post-glacial period are available for the Canadian boreal forest but charcoal analyses at eastern sites have shown that fire activity has increased during the late Holocene climatic cooling (Filion et al. 1991; Carcaillet & Richard 2000).

It is generally speculated that long-term vegetation dynamics in boreal and temperate forests are controlled by change in fire (Mehringer et al. 1977; Anderson et al. 1986; Rhodes & Davis 1995; Hörnberg et al. 1999; Tinner et al. 1999). However, charcoal and pollen analyses at the southern limit of the mixed-boreal forest in Ontario do not disclose any such relationship (Cwynar 1978; Fuller 1997) and vegetation composition also appears independent of changes of fire frequency in north-west Wyoming (Millspaugh et al. 2000). Nevertheless, there is some evidence for a relationship between vegetation and fire in the Atlantic Canadian boreal forest (Green 1982). In the extreme northern boreal forest, it has been suggested that fire has triggered landscape fragmentation over several millennia, without any change in the location of the northern tree-line (Payette & Lavoie 1994). Changes in flammability may explain the occurrence of different fire regimes through time, both in conifer and broad-leaved forests (Clark 1988; Clark et al. 1996a,b). Vegetation and fire change almost in synchrony (Clark et al. 1996a), and either could be the driving force. An influence of fuel on the fire regime is difficult to demonstrate and remains unclear during the Holocene but would require significant change in vegetation proxy to be shown to precede a change in fire regime.

We assessed whether any vegetation change could explain the fire frequency changes during the Holocene and, if not, whether climate change could be responsible. We compared pollen data with reconstructed fire frequency history at the same sites. If the fire frequency changes were due to differences in vegetation composition, we predict differences in the relative abundance of low flammable/combustible trees (e.g. Populus, Betula, Salix, Alnus, Acer), and species such as Pinus, Picea and Abies. At the stand level, broad-leaved species, particularly Populus and Betula, limit fire propagation owing to their low fuel quality (Hély et al. 2000a) but changes in abundance will take a few decades to centuries before they have an effect on fire regime. We also compared fire history with hydro-climatic reconstructions independent of fire and vegetation, e.g. using δ18O or lake-levels as proxy data.

Study site

  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References


Lac Francis, Lac Pas-de-Fond and Lac à la Pessières are head lakes located in western Québec, south of James Bay near the boundary with Ontario (Fig. 1). In this area, till outcrops are scattered within a more or less uniform and flat landscape. The lakes lie on eskers covered by clay sediment from the proglacial lake Ojibway that deposited the ‘Northern Clay Belt’, covering a large area south of James Bay (Veillette 1994). Lake Ojibway disappeared abruptly when the residual Laurentide ice-sheet collapsed, allowing the northward outflow of proglacial fresh water to Hudson bay c. 8400 cal. year BP (Barber et al. 1999). Subsequently, accumulated sediment is expected to be predominantly organic.


Figure 1. Location of studied lakes in Québec, east Canada.

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The three lakes are located along a vegetation gradient, with the southernmost, L. Francis, in mixed-boreal forest, L. Pessière in the coniferous-boreal forest and L. Pas-de-Fond at the northern edge of the present-day limit of mixed-boreal forests (Fig. 1). The sites are separated by c. 100 km and therefore differ in climate as well as vegetation.

All three lakes are small and highly coloured, and except for Francis are dimictic closed-basins with a small outflowing brooklet (properties given in Table 1). The water columns show strong thermal stratification, with the thermocline occurring at 1.5 m to 4 m depth depending on lake size, and the hypolimnion strata becoming rapidly anoxic.

Table 1.  Description of lakes and main features of the chronology
 L. FrancisL. Pas-de-FondL. à la Pessière
Latitude48°31′35″ N48°48′30″ N49°30′30″ N
Longitude79°28′20″ W78°50′00″ W79°14′25″ W
Elevation305 m290 m280 m
Vegetation zoneMixed boreal forestMixed boreal forestConiferous boreal forest
Local vegetation around
lakesPicea marianaPopulus tremuloidesPicea mariana
 Pinus banksianaAlnus viridis 
 Abies balsameaCultivated areas 
 Betula papyrifera  
Lake surface0.8 ha2 ha4 ha
Max. lake depth6 m11 m16 m
Inlet/OutletYes (intermittent)/NoNo/YesNo/Yes
Type of corersLivingstoneLivingstoneMcKereth
LaminatedYes (78%)Yes (100%)Yes (100%)
Total length of sediment302 cm368 cm584 cm
Post-glacial chronology6800 cal year7450 cal year7650 cal year
Deposition time26 year cm−123 year cm−113 year cm−1
± SD (SE)±11.7 (0.67)±8.7 (0.49)±2.7 (0.11)


At the retreat of the post-glacial lake Ojibway, 8400 years ago, orbital forcing led to the climate being warmer in summer and colder in winter than at present (Kutzbach et al. 1998). Mean summer temperatures have progressively decreased with some oscillations, e.g. during the Little Ice Age and the Warm Medieval Period. Lake levels have also changed several times, suggesting changes in the precipitation regime, being low between 6200 and 3800 years ago (northern Québec; Payette & Filion 1993), or between 11 000 and 4400 years, apart from intermediate levels at 7000–6000 years (southern Québec; Lavoie & Richard 2000a). Combined interpretation of δ18O, lake level and charcoal analyses suggests, during the last 3000 years, changes towards wetter winters and more frequent drier summers (Carcaillet & Richard 2000).


The south part of the Clay Belt is characterized by mixed-boreal forest, i.e. a closed-crown forest containing Abies balsamea (L.) Mill. and Betula papyrifera March. Late successional communities are generally dominated, on mesic sites, by Abies balsamea, Thuja occidentalis L. and Picea glauca (Moench) Voss. and, on xeric sites, by T. occidentalis and Picea mariana (Mill.) BSP. On mesic sites early successional communities following natural disturbances are characterized by the occurrence of Salix spp., Prunus pensylvanica L.f. and the abundance of Populus tremuloides Michx. and Betula papyrifera (Bergeron 2000; Gauthier et al. 2000).

On the mesic soils around L. Francis, the overstorey is now dominated by Picea mariana and Abies balsamea, but Pinus banksiana Lambert is still abundant in the area and was present on the shore as late as the most recent fires (ad 1760). Pinus strobus L. and Pinus resinosa Ait. are present but are close to their northern limits (500 m and 5 km away, respectively; Bergeron & Brisson 1990; Bergeron et al. 1997). The present-day vegetation at Pas-de-Fond is influenced by agricultural land-use, but the lake is located at the northern limit of the mixed-boreal forest and c. 20 km south of the Holocene northern limit of Pinus strobus (Terasmae & Anderson 1970).

L. à la Pessière is in coniferous-boreal forest. Such closed-crown forest is characterized by thick humus layers covered by Hypnaceae and is dominated by Picea mariana throughout succession (Gauthier et al. 2000), although Populus tremuloides and Pinus banksiana are abundant at early stages. Lichen forests, dominated by Pinus banksiana, abound on dry sites (e.g. moraines and esker deposits), but other species such as Abies balsamea or Thuja occidentalis are scarce and are generally found only on lake shores. Some regeneration of Abies balsamea has been observed in a recent clear cut on productive soil a few hundred metres from L. à la Pessière, but most of the surroundings area is covered by old growth Picea mariana swamp-forest. Throughout the study area, logged areas contain abundant Populus tremuloides, Betula papyrifera and Alnus viridis crispa (Ait.) Pursh.


Trees colonized the lowlands immediately after the retreat of proglacial Lake Ojibway without an initial tundra phase. A boreal-type vegetation (Richard 1980; Liu 1990) developed from tree species already present on the southern shore and the islands of proglacial lake, under the settled interglacial Holocene climate. Populus, Picea mariana and Pinus banksiana dominated early dynamics around southern sites but between 7200 and 3250 BP (7900 and 3450 cal. years BP) the forest was characterized by Pinus strobus and Thuja occidentalis. The late Holocene is characterized by an increasing abundance of Abies balsamea, Pinus banksiana and Picea mariana (Terasmae & Anderson 1970; Richard 1980; Liu 1990).

No pollen data are available for the northern part of our study area, but pollen analyses for similar vegetation to the north and east indicate that the vegetation has been dominated by Picea mariana, associated with Betula and Alnus viridis, since deglaciation. Few major changes appear to have affected the coniferous-boreal region north to the forest-tundra during the Holocene (Garralla & Gajewski 1992; Gajewski et al. 1993; Gajewski et al. 1996).


The principal features of fire history in Québec during the Holocene are that activity was high 10 000–7500 cal. year BP and low 7500–2500 cal. year BP, increasing subsequently but remaining lower than before 7500 cal. year BP. This pattern, deduced from charcoal analysis of 30 lakes located in east Canada (Carcaillet & Richard 2000), matches that inferred from charcoal dating in soil, dunes and peat in northern Québec (Filion et al. 1991).

As the Little Ice Age ended (c. ad 1850), the fire frequency decreased due to the increasing summer moisture associated with global warming (Bergeron & Archambault 1993). In the southern boreal forest, fires were larger and more frequent prior to the 20th century (Bergeron 1991; Dansereau & Bergeron 1993), with fire cycles for sites at 48–50° N estimated at about 132 years before ad 1850, increasing to 234 years and, since ad 1920, 521 years (Bergeron et al. 2001).

In Canada, fires now occur only during intervals with low precipitation, when a long sequence of days with less than 1.5 mm of rain or with relative humidity less than 60% allows the litter layer to become dry. Strong winds and high summer temperatures also contribute to creating the critical conditions for fire (Flannigan & Harrington 1988; Harrington & Flannigan 1993), although the abundance of lightning controls the number of fires initiated (Flannigan & Wotton 1991). Ignition and spread of fires in the boreal forest occurs mainly when high-pressure systems with strong atmospheric instability are dominant for at least 3 days on which there is less than 1.5 mm of precipitation (Flannigan & Harrington 1988; Nash & Johnson 1996), particularly in late-spring or early summer, when the snow cover has totally melted but the broad-leaved trees are not fully flushed. In Québec, both Arctic cold/dry and the Polar/Pacific cool/dry air masses can cause drying conditions (Phillips 1990), but only the later create the critical conditions for ignition (Johnson 1992).


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References


At Lakes Francis and Pas-de-Fond, lacustrine sediments were recovered from the frozen surface with a Livingstone corer, whereas a McKereth sampler equipped with a 6-m length tube was used at Lac à la Pessière. Because neither corer allows sampling of the more recently accumulated material, the water–sediment interface was sampled using a Kajak-Brinkhurst (KB) gravity corer (to give 21 cm, 28 cm and 42 cm cores with intact water–sediment interfaces at Francis, Pas-de-Fond and à la Pessière, respectively). The pair of cores for each site were cross-correlated by pollen analyses and loss-on-ignition (LOI) measurements in order to estimate the thickness of the sediment missing from the surface of Livingstone and McKereth cores.


The Livingstone, McKereth and KB cores were sliced into centimetre sections and 1 cm3 subsamples taken along the longitudinal axis of the core. Sediment samples were sieved through 150-µm mesh (Carcaillet et al. 2001), because charred particles larger than 100–150 µm are unlikely to be transported more than a few hundred metres from the source area (Wein et al. 1987), and particles larger than 500 µm no more than a few metres (Clark et al. 1998; Ohlson & Tryterud 2000). Sediments were deflocculated in a 3% Na4P2O7 solution for a minimum of 2 days before a gentle manual water spray was used to aid sieving. The remaining particles were bleached in a Javel water solution (10%) for a few minutes to clearly distinguish charcoal fragments from dark organic matters. The surface area of each charcoal fragment was estimated microscopically at 40 × magnification using a graticule with 400, 0.0144 mm2, squares and was classified into one of 10 exponential size-classes: < 0.1197 mm2; 0.1197–0.2394 mm2; 0.2394–0.4788 mm2; 0.4788–1.0773 mm2; 1.0773–1.9152 mm2; 1.9152–2.9925 mm2; 2.9925–5.9850 mm2; 5.9850–11.9700 mm2; 11.9700–23.9400 mm2; > 23.940 mm2. The total surface area of charcoal in a sample was obtained by summing the mean surface area of each size-class multiplied by the number of particles in that size-class over all classes. Charcoal measurements are reported as areal accumulation rates (mm2 cm−2 year−1).


Pollen and spores were analysed according to Fægri et al. (1989), with exotic pollen (Eucalyptus) added to each sample in order to estimate the pollen concentration. Samples were deflocculated with 10% hot KOH and sieved through a 700-µm mesh. Carbonates, silicates and most of the organic matter were removed with 10% HCl, 48% HF and acetolysis, respectively, before mounting in glycerine. A minimum of 500 grains was counted per sample. Pollen counts at Francis and à la Pessière were planned to give a mean time resolution of about 100–120 years and samples were taken every 5 cm (2–3 cm at the surface and during afforestation phases) and every 8 cm (4 cm at surface), respectively. Preliminary analysis of Pas-de-Fond cores at low resolution (17 spectra on > 8000 years) showed similar results to Francis (in the same vegetation zone at present), and further analysis was unlikely to yield significant additional information.


To obtain an accurate age/depth model for detailed reconstructions, the sedimentation rate of the KB cores was estimated using 210Pb dating based on alpha spectrometry with 210Po. Measurements were obtained for L. Francis and Pas-de-Fond (six per core, Table 2) but a technical problem resulting from sediment storage unfortunately prevented 210Pb measurements at L. à la Pessière.

Table 2.  Radioactive lead dates of lakes Francis (FRANCIS) and Pas-de-Fond (PFOND) from measurements carried out at GEOTOP, Université du Québec à Montréal and calculated using the constant initial concentration (CIC) model
Sample depth in the KB core (cm)Laboratory number210Pb activity (dpm g−1)210Pb date (year AD)
FRANCIS KB-3GEOTOP-193723.59451967
FRANCIS KB-7GEOTOP-193815.79731953
FRANCIS KB-11GEOTOP-1939 6.00031912
FRANCIS KB-15GEOTOP-1940 3.14421868
FRANCIS KB-19GEOTOP-1941 2.81031854
FRANCIS KB-21GEOTOP-1942 2.4438Unrealistic
PFOND KB-3GEOTOP-194341.3411934
PFOND KB-7GEOTOP-194427.0371920
PFOND KB-11GEOTOP-194511.5701893
PFOND KB-15GEOTOP-1946 1.2821822
PFOND KB-19GEOTOP-1947 1.0551816
PFOND KB-21GEOTOP-1948 0.007Unrealistic

Radiocarbon dating of terrestrial plant macro-remains in L. Francis and Pas-de-Fond was carried out by accelerator mass spectrometry (AMS) (Table 3). A pool of terrestrial plant macro-remains was preferred to bulk sediments to avoid any ‘hardwater’ effect on 14C dating. Macroremains were rare in the à la Pessière core and radiometric dating was therefore carried out on bulk sediment (Table 3). However, there was sufficient material for AMS dating of terrestrial plant macroremains immediately below the clay–gyttja interface, and this allowed us to correct the date at the bottom, as obtained from the bulk sample for the influence of carbonates (Fig. 2). The 14C measurements were calibrated to dendrochronological years (Stuiver et al. 1998).

Table 3.  Radiocarbon dates of lakes Francis (FRANCIS), Pas-de-Fond (PFOND) and Pessière (PESSIERE). The depths correspond to measurements on the cores before palyno-stratigraphic correlation with Kajak-Brinkurst cores
Sample depth inNature of the dated sample the core (cm)Laboratory no.*14C dates (years BP)Calibrated dates (years BC/AD)
  • *

    TO: Isotrace Radiocarbon Laboratory, Accelerator Mass Spectrometry Facility, University of Toronto (Toronto, Ontario). Beta: Beta Analytic Inc. (Miami, Florida).

  • Conventional radiocarbon years BP (before ad 1950). The dates are corrected for natural and sputtering fractionation to a base of δ13C = −25‰.

  • Calibrated according to C14CAL98 programme (Stuiver et al. 1998). Reported as intercept midpoint with 2 σ range.

FRANCIS 23–26Picea mariana twig cushion, microspore and leaf, Larix laricina leaf and seed, wood fragmentsTO-7076 490 ± 801400 AD–1460 AD
FRANCIS 77–88Woods fragments, Myrica gale bark, Larix laricina leaf fragmentsTO-64731080 ± 50 880 AD–1030 AD
FRANCIS 102–103Larix laricina and Picea mariana, leaf fragments, Larix/Picea bark and wood fragmentTO-64741820 ± 70 230 AD
      60 AD–405 AD
FRANCIS 135–138Larix laricina leaf fragments and seed, Betula papyrifera and Chamaedaphne seedTO-64752110 ± 120 400 bc–135 AD
FRANCIS 1909–191Abies balsamea and Larix laricina leaf fragments, Pinus strobus staminate scalesTO-64763620 ± 702140 bc–1755 bc
FRANCIS 221–222Larix laricina leaf fragments, Pinus strobus male cone scaleTO-70774800 ± 603700 bc–3500 bc
FRANCIS 240–241Larix laricina leaf, Pinus strobus male cone scale, Pinus banksiana leaf fragmentsTO-70785200 ± 1004250 bc–3785 bc
FRANCIS 258–259Pinus strobus staminate scales and wood fragments, Larix laricina, Picea mariana and Taxus canadensis leaf fragmentsTO-64775870 ± 704910 bc–4545 bc
FRANCIS 294–296Wood fragments, charcoal, Larix laricina leaf fragments, Myrica gale barkTO-64786420 ± 1205530 bc–5200 bc
PFOND 59.5–62.5Picea type mariana needle, sterignemata and megaspores, Larix laricina needle and seed, Andromeda leaf, conifer bark; Pinus strobus cone scaleTO-78421580 ± 70 335 ad–620 ad
PFOND 121.5–128.5Wood fragment, bark, Chamaedaphne seed, Larix laricina needles, Picea sp. seed and needles, Pinus strobus seedTO-78433160 ± 701530 bc–1285 bc
PFOND 184.5–187.5Pinus strobus cone scale, Picea mariana seed, Larix laricina needles, Betula pa pyrifera seedTO-78444810 ± 903775 bc–3485 bc
PFOND 215.5–220.5Pinus strobus cone scale and needlesTO-78455030 ± 703975 bc–3655 bc
PFOND 273.5–281.5Betula papyrifera seed and bract, Picea mariana needlesTO-78465860 ± 1705080 bc–4350 bc
PFOND 317.5–322.5Betula papyrifera seed, Larix laricina needles, conifer bark, wood fragment, Carex seedTO-78476920 ± 1306025 bc–5615 bc
PESSIERE 75.5–80.5Laminated gyttjaBeta-1334661510 ± 90 385 ad–675 ad
PESSIERE 167.5–172.5Laminated gyttjaBeta-1334652500 ± 80 815 bc–395 bc
PESSIERE 290.5–295.5Laminated gyttjaBeta-1334643410 ± 601885 bc–1535 bc
PESSIERE 398.5–394.5Laminated gyttjaBeta-1334634580 ± 703515 bc–3090 bc
PESSIERE 487.5–492.5Laminated gyttjaBeta-1334616010 ± 705060 bc–4725 bc
PESSIERE 538.5–543.5Laminated carbonated gyttjaBeta-1334627500 ± 906475 bc–6205 bc
PESSIERE 545.5–550.5Picea type mariana needle and seed, Larix laricina needle, wood fragment, Epilobium cf. glandulosum seed, Choristoneura faeces, Typha seedTO-83056720 ± 805735 bc–5505 bc

Figure 2. Age/depth model based on AMS 14C dates for terrestrial plant macro-remains and 210Pb measurements on upper sediments in Lac Francis and L. Pas-de-Fond. At L. à la Pessière, radiometric 14C measurements on bulk sediment were corrected according to the single obtainable AMS dating on macro-remains. A basal layer of carbonated blue-grey clay is overlain by gyttja which is alternating laminated and non-laminated in L. Francis, and totally laminated in L. Pas-de-Fond and L. à la Pessière.

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The sedimentation rate varies through time and thus triggers changes in the deposition time. Sampling cannot take these natural variations of sedimentation rate into account, except in varved, annually laminated sediments (Clark 1990; Clark et al. 1996b; Larsen & MacDonald 1998). The initial charcoal series was therefore decomposed from one with variable time resolution (Fig. 3) to one at a constant resolution. The mean time resolution of samples was 26, 23 and 13 year in Francis, Pas-de-Fond and à la Pessière, respectively (Table 1), but at Francis the deposition time over the last 1000 years, and thus the mean time resolution over the post-glacial, is much reduced. Transformation to constant time resolution (Fig. 4a) therefore employed the mean time resolution from the onset of organic accumulation to 1000 years ago (35, 24 and 14 years, respectively, for the three lakes). Series for Pas-de-Fond and à la Pessière were also computed with a constant time resolution of 35 years (Fig. 4b) to check whether differences in mean time resolution per lake created an effect, and to compare the post-glacial pattern of fire intervals between lakes. All transformations to equally spaced time series were performed via a spline function using PPPhalos software (Guiot & Goeury 1996).


Figure 3. Raw data for charcoal accumulation rates with uneven time resolution.

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Figure 4. Charcoal series transformed to equally spaced time resolution. Crosses indicate the peaks of charcoal that were used for the fire reconstruction. (a) Using mean deposition time, calculated separately for each lake between the onset of organic sedimentation and 1000 years ago. (b) Using the coarsest mean time resolution between the three lakes (i.e. 35 years at L. Francis) to estimate the role of resolution on the fire frequency reconstruction. Charcoal peak frequency is similar to Fig. 3 although many peaks are reduced in height, particularly in (b). The thick lines indicate the background value modelled using an inverse Fourier transform with a window-size of 100 years.

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Fire intervals are computed by detrending the charcoal accumulation rate and then measuring the time between two peaks. Local fires are assumed to generate individual peaks of charcoal above a background level derived from fires on a regional scale (Clark & Royall 1996) or from charcoal sequestered in the catchment area and its lacustrine littoral zone. The latter represents accumulation over a protracted period before final sedimentation in the deep-water sediments (Earle et al. 1996; Whitlock & Millspaugh 1996). Consideration only of particles larger than 150 µm excludes charcoal produced by regional burning (Carcaillet et al. 2001) and detrending allows removal of the remaining background signal. It is based on a modelled low-frequency signal using an inverse Fourier transform computed with the PPPhalos software. The detrended series represents the residue after subtracting the Xt° modelled low-frequency signal from the charcoal accumulation rate Xt. This method is preferred to the ratio between Xt and Xt° used for data from pollen-slides (Bergeron et al. 1998). The charcoal background is much lower than on pollen-slides (Carcaillet et al. 2001) and further amplification is not needed to distinguish the peaks. Several low pass filters (3–20 data points wide) were tested and a window of 3 points was found to give the best exclusion of background signal.

Fire interval then corresponds to the time between two charcoal peaks above a given threshold (Bergeron et al. 1998; Long et al. 1998). The fire-event threshold can be estimated by comparing the local fire history, reconstructed by dendrochronological analysis of fire scars, with the charcoal peaks (Long et al. 1998), assuming that most severe fire events are detected by charcoal analysis (Clark 1990; Millspaugh & Whitlock 1995). In our study area, most forest communities develop after stand-replacing fire that leaves few fire scars, and reconstruction of fire history is therefore difficult. The last local fire at Francis was in ad 1760, and fires at Pas-de-Fond between ad 1916–20 may be due to the first ‘European Canadian’ settlements there. No fire scars have been found on spruce in the old growth forest around Pessière. The time since last fire has been estimated from the age of oldest tress (at least 250 years), but this is less than that indicated by 14C dating of organic material accumulated immediately above the last charcoal layer in forest humus (about 650 years; Cyr et al. 2000). Because of these problems, any peak whose score was higher than the standard deviation of the average of the detrended charcoal series was considered as a fire event. To test for differences in fire frequency, the mean intervals were modelled using Weibull survival data analysis (Clark 1989; Johnson & Gutsell 1994), regarding the last interval (time since last fire) as a minimum estimate.


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References


Both Lac Francis and L. Pas-de-Fond show a rise in charcoal accumulation rate over the last 2000 years (Fig. 3). At L. à la Pessière, the rate increase is earlier (around 3500 years ago) and is followed by a decrease 1000 years ago. The transformation of raw data from non-equally (Fig. 3) to equally spaced time resolution (Fig. 4) does not significantly modify these patterns, even if the transformation is based on a coarse deposition time of 35 years (Fig. 4b).

All three sites show a fall in the Holocene fire interval (2200–2000 years ago at Francis and pas-de-Fond, 3300 years ago at à la Pessière) followed by an increase c. 1300 years ago at Francis and à la Pessière (Fig. 5a). When the three lakes were compared using a common equally spaced time resolution of 35 years, Pas-de-Fond seems to have experienced longer fire intervals in the last 500 years and therefore a decrease in the local fire frequency compared with Francis and à la Pessière, which are similar to each other (Fig. 5b). The timing of changes in fire regime is not significantly affected by adapting the coarse equally spaced time resolution of 35 years for all lakes (Fig. 6), nor is the structure of fire intervals affected (Fig. 7). The reconstruction for à la Pessière is most affected (resolution shift from 14 years to 35 years) but the pattern is preserved.


Figure 5. Fire interval history, deduced from charcoal series transformed in equally spaced time resolution with (a) the mean deposition time per lake and (b) using a constant 35 years resolution.

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Figure 6. Pattern of cumulated fire events plotted against time for fire reconstruction deduced from charcoal series transformed in equally spaced-time resolution with (a) different and (b) equal time resolutions for the three lakes.

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Figure 7. Distribution of reconstructed fire intervals over the post-glacial from charcoal series transformed to equally spaced time resolution (as indicated).

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The pattern of changes of fire frequency can be summarized by calculating the mean fire interval (MFI) for each lake (Table 4). Pas-de-Fond shows only two main phases, Francis and à la Pessière show an additional recent increase since about 1000 years, and à la Pessière a fourth fire-prone period between 7650 and 7300 cal. year BP (see also Fig. 5). For all three 35-year series, MFI were two–three times as long during the mid-Holocene (Fig. 8a–c) as in the late Holocene (Fig. 8d–f). The pattern for the late Holocene is similar for all three lakes, except if we include the present-day fire-free interval at à la Pessière (Fig. 8d). The mid-Holocene is less homogeneous, with à la Pessière showing no fire intervals longer than 750 years, whereas values reach c. 1300 years at Pas-de-Fond and c. 1600 years at Francis. Significant differences in mean fire interval are of the same order of magnitude when estimated using a simple arithmetic average or the Weibull model (Table 4), although the latter values, also corresponding to the fire cycle, are generally smaller. The parameter c of the Weibull model is significantly larger than 1 for all periods, indicating that the hazard of burning increases with time since the last fire: 1.32 (2.21), 1.36 (1.66) and 1.66 for à la Pessière, Pas-de-Fond and Francis, respectively, with values at 35 years resolution is in parentheses.

Table 4.  Arithmetic and modelled mean fire intervals (MFI) and standard deviation for Lac à la Pessière (PESSIERE), Lac Pas-de-Fond (PFOND) and Lac Francis (FRANCIS). Mean fire intervals are calculated for the series of equally time-spaced intervals based on the mean deposition time for each lake, and for the coarsest equally time-spaced interval. e(t) is the Weibull modelled MFI and µ the arithmetic MFI
SériesPeriod (cal. yr BP)µ ± σ (SE) (yr)e(t) [σ] (yr)
PESSIERE 14 yr7650–7300 bp 49 ± 20 (7) 54 [28–102]
 7300–3300 bp210 ± 167 (38)145 [64–325]
 3300–1300 bp 64 ± 55 (10) 55 [28–105]
 1300–0 bp439 ± 115 (199)337 [131–867]
PESSIERE 35 yr7650–7350 bp111 ± 86 (43) 77 [29–206]
 7350–3400 bp420 ± 225 (75)227 [67–775]
 3400–1400 bp200 ± 80 (24)120 [41–355]
 1400–0 bpNo peak585 [139–2475]
PFOND 24 yr7450–2000 bp271 ± 272 (60)187 [69–505]
 2000–0 bp 88 ± 42 (9) 64 [29–102]
PFOND 35 yr7450–2000 bp340 ± 293 (75)214 [66–692]
 2000–0 bp154 ± 60 (17) 94 [35–252]
FRANCIS 35 yr6800–2200 bp502 ± 466 (155)282 [75–1063]
 2200–1000 bp115 ± 45 (13) 67 [25–181]
 1000–0 bp203 ± 83 (37)131 [42–411]

Figure 8. Distribution of reconstructed fire frequencies for each lake for the main periods with long (a, b, c) and short (d, e, f) fire intervals. All data are displayed except for à la Pessière between 7650 and 7350 cal. years BP, where few fires (n = 3 fires, MFI = 111 ± 86, see Table 4) were recorded.

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The fire intervals are strongly influenced by the resolution used. Thus, changing the resolution at à la Pessière from 14 years to 35 years, causes many peaks to disappear and the mean fire interval to increase from 210 to 420 years between 7300 and 3300 years ago, and from 64 to 200 years between 3400 and 1200 years ago (Table 4). Reconstructed fire intervals cannot therefore be used as a proxy to discuss the magnitude of change through time without consideration of the resolution. At à la Pessière it is, however, obvious that the fire intervals have changed three times since 7650 years, at c. 7300, c. 3300 and c. 1300 cal. years BP (Table 4), and the magnitude of these changes can be used to discuss both the causes that trigger the fire frequency and the consequences in terms of vegetation. For all sites, mid-Holocene fire intervals are longer than those in the late Holocene, although the change occurred earlier in coniferous boreal forest (à la Pessière) than in mixed boreal forest, Pas-de-Fond and Francis (Fig. 5). The patterns were similar, regardless of the method of transformation of the time-resolution (Fig. 7) or of estimating the MFI (Table 4).


Pollen diagrams summarize the vegetation history around the three lakes (Figs 9–11). The moderate size of the lakes (0.8–4 ha; Table 1) ensures that sediments have mostly recorded local pollen (Jacobson & Bradshaw 1981; Koff et al. 2000) in the post-glacial period (dates in Table 1), before this sediments rich in clay and poor in pollen derive from residual waters of proglacial Lake Ojibway, and include pollen grains transported long distances by air or in surface runoff.


Figure 9. Summary frequency terrestrial pollen diagram of Lac Francis. The frequency is calculated on the terrestrial taxa. The vertical line is the onset of organic sedimentation associated with the major rise of pollen concentration, both corresponding to the settlement of terrestrial vegetation on the lake shore.

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Figure 10. Summary frequency terrestrial pollen diagram of Lac Pas-de-Fond. Legend: see Fig. 9.

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Figure 11. Summary frequency terrestrial pollen diagram of Lac à la Pessière. Legend: see Fig. 9.

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At Francis, afforestation first occurred between 6800 and 6000 cal. years BP as shown by the abundance of Populus, Salix and Alnus type viridis and of herbs such as Cyperaceae and Poaceae (Fig. 9). Subsequently the forest was dominated by Pinus strobus and Taxus canadensis, then by Thuja/Juniperus and finally by Betula. Between about 6000 and 1000 years ago, the pollen diagram shows a slight but continuous decrease in abundance of Pinus strobus, Taxus, Thuja/Juniperus and Populus and a rise in Betula and Alnus type incana. The only abrupt change occurred at about 1300 years cal. BP, when Abies, Picea type mariana became the dominant pollen taxa preceding a rise in Pinus cf. banksiana and Alnus type viridis. The pollen diagram did record any abrupt change in vegetation composition preceding the change in fire frequency at 2200 cal. years BP.

The low resolution analysis of Pas-de-Fond shows a pollen record broadly similar to Francis, apart from higher frequencies of Betula and Picea type mariana over the post-glacial and no rise of Abies during the late Holocene (Fig. 10). The early mid-Holocene (7400–4000 cal. years BP) succession is therefore similar except for recent dominance by Picea type mariana and the continued presence of Larix laricina, a strict local dispersal taxa (5000–1000 cal. years BP).

Afforestation at à la Pessière started at 7650 cal. years BP and was immediately characterized by an abundance of Picea type mariana (Fig. 11). The early Holocene successional species seen at Francis were never abundant here and decreases in Thuja/Juniperus at 4500 cal. years ago, and again during the last 600 years, are the only major changes recorded for the last 7000 years. There is a slight progressive increase of Picea type mariana, and a decrease of Pinus strobus and Taxus, while Pinus cf. banksiana, Populus cf. tremuloides and Alnus type viridis have increased during the late Holocene. The main features of the L. à la Pessière pollen diagram are the strong stability and the high abundance of Picea type mariana.

The similarity of Pas-de-Fond to Francis in the mid-Holocene (7400–4000 cal. years BP) but to à la Pessière in the late Holocene may be related to its vicinity to the present-day limit between mixed-boreal and coniferous-boreal forests (Fig. 1), which may have been displaced southwards around 3500 cal. years BP, as suggested by increases in Picea type mariana and Alnus type viridis.

Juniperus is rare and never abundant in terms of biomass in the study area, and the pollen taxon Thuja/Juniperus thus probably represents mostly Thuja occidentalis: we therefore refer to it as Thuja hereafter.


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References


The observed increase in hazard of burning with the time since last fire could be due to stand-level vegetation dynamics controlling the local fire ignition and spread, to critical weather conditions being infrequent, or to both fuel and weather acting on fire activity.

The rate of accumulation of fuel (living biomass, coarse woody debris), its distribution or connectivity (vegetation ± packed or fragmented) and quality (flammability of species) can all affect the risk of burning. In the present-day mixed-boreal forests, significant fuel build-up is observed when fire intervals exceed 5 decades and reaches a plateau at around 150–200 years (Hély et al. 2000b). Apart from the last 1300 years at à la Pessière, our late Holocene reconstructions based on equally spaced time resolution fall within this range (Fig. 8d–f) although it should be borne in mind that mean fire interval is lower at finer resolution (Table 4, Fig. 5) and that some real fire events may not have been recorded. The quality and structure of fuel accumulation changes with stand composition: the first decades are dominated by Populus, Salix and Betula, and these are succeeded beyond 150 years by conifers, i.e. Abies, Picea and Thuja (Bergeron 2000; Gauthier et al. 2000). Fuel is more flammable and fire spreads much better in stands dominated by conifers rather than broad-leaved species such as Populus and Betula (Hély et al. 2000a). Changing stand composition could therefore contribute to the observed increase in hazard of burning with time since the last fire. However, we should then expect changes in pollen assemblages to precede changes in fire frequency: dominance by highly flammable conifers before an increase and by broad-leaved species before a decrease.


The increase in fire frequency between 3000 and 2000 cal. years BP is obviously not triggered by vegetation composition: the pollen diagrams show rather stable vegetation that, particularly at à la Pessière, has been dominated by conifers over the last 7000 years, and of the weak vegetation changes observed at Francis and Pas-de-Fond; none occurs several hundred years before the change in fire frequency. The communities were dominated by broad-leaved species only during initial afforestation, although early coniferous species (Thuja and Pinus strobus) in mixed-boreal sites were replaced by vegetation more productive in pollen of Betula, before Picea, Pinus banksiana and Abies took over. The coniferous-boreal forest has been very stable since afforestation c. 8000 years ago.

Similar development of Picea mariana and of Pinus banksiana from the early middle to late Holocene have been highlighted by pollen analysis in coniferous-boreal forest 300 km eastward (Garralla & Gajewski 1992) and 500 km northward (Gajewski et al. 1993), as well as in mixed-boreal forest both around Lac Francis (Richard 1980) and 250 km westward (Liu 1990). Our pollen diagrams are very similar to those obtained from other sites with similar present-day vegetation, suggesting that they are good representations of processes that have affected vegetation on a large biogeographical scale. None of the studies carried out in the coniferous- or mixed-boreal forests between 75° W to 82° W and 47° N to 50° N (e.g. Vincent 1973; Richard 1980; Liu 1990; Garralla & Gajewski 1992) have indicated an abrupt change in the forest composition preceding the date at which we have recorded changes in fire frequency (Figs 4 and 5).

There are significant changes in our pollen diagrams (Figs 9–11) and in those from the previous studies (Richard 1980; Garralla & Gajewski 1992; Gajewski et al. 1993) only during initial afforestation phase, but fire interval did not rise until several millennia later. Earlier afforestation at à la Pessière when east Canada experienced high fire incidences (Carcaillet & Richard 2000) is reflected in a short period with low fire interval. Fire frequency at the mixed-boreal sites shifted about 2000 years ago but the shift towards pollen indicating a more flammable vegetation occurred later at Francis (1300 cal. years BP) and too much in advance for it to determine fire regime at Pas-de-Fond (3500 cal. years BP).

As well as vegetation affecting fuel combustibility, composition can influence connectivity (structure is ± packed). The combined effects of fires and climate cooling have led to more open or fragmented communities at the northern limit of the boreal forest over the last 2000 years without retreat of the tree-line (see Payette & Lavoie 1994). However, in the hearth of the boreal forest, there is no obvious evidence of opening or fragmenting processes that might have modified fuel connectivity and density (Gajewski et al. 1993), and this is supported by a stable pollen diagram as at à la Pessière. Even the fall in pollen concentration at Francis after 2000 cal. years BP that could result from decreasing density of trees, could also be due to lower per-tree production, or simply to a local change in the sedimentation rate. In the absence of unequivocal supporting data we conclude that the vegetation in the coniferous- and the mixed-boreal forest is unlikely to have controlled fire frequency during the Holocene. In the mixed-boreal forest, the fire regime at broad scale is thus probably primarily controlled by external processes, with the increasing fire hazard around lakes being due to the occurrence of critical weather for fire ignition and spread. At the stand-level, however, fuel build-up or quality may influence fire spread.


Changing fire regimes between 3000 and 2000 cal. years BP have also been inferred from analysis of pollen-slide charcoal at low time resolution analysis of 30 lakes through east Canada (Carcaillet & Richard 2000). Fire history inferred from pollen-slide charcoal series mostly reflects regional burning activity (Clark & Royall 1996; Tinner et al. 1998; Carcaillet et al. 2001), but despite the differences in terms of approaches, quality of sites and resolution of analyses between the studies carried out in Québec, both conclude that the middle Holocene was less conducive to fire than the late Holocene. The change (up to an increase in frequency) occurred earlier in the coniferous-boreal than in the mixed-boreal forest (3500 vs. 2000 cal. years BP) and may indicate more frequent intrusion of cool/dry Pacific or cold/dry Arctic air masses increasing drought in the potential fire seasons during late-spring or summer.

The eastern Canadian fire status derived by Carcaillet & Richard (2000) is biased towards the current mixed-boreal forest, where 14 of their 30 lakes were located. Only one lake (Lac Desautels) in the present-day coniferous-boreal forest was studied, but despite the low resolution analysis, charcoal accumulation rate appeared highest between 3500 and 1000 cal. years BP (Carcaillet & Richard 2000). The early change at à la Pessière, matching that of L. Desautels, may therefore be typical of coniferous-boreal forest and may indicate that the factors forcing fire change act from the north or north-west. The northerly Arctic air mass is very stable and is rarely associated with lightning. It is therefore probably north-west influences, due to more frequent incursions of unstable dry Pacific air masses, that create the critical weather for fire ignition and spread.

The transition between middle to late Holocene is associated with increasing lake water table both in Québec (Lavoie & Richard 2000a), and generally in north-east North America (Harrison 1989; Yu et al. 1997). Although this suggests a wetter climate in the late Holocene, the additional precipitation is concentrated in winter and can thus control the water table (Carcaillet & Richard 2000), while decreased summer precipitation favours fire. δ18O analyses indicate a decrease of the summer relative humidity in north-central and south-east Canada over the last 2000–3000 years (Edwards et al. 1996) and although the timing is not yet precisely known, charcoal, lake-level and δ18O series combine to suggest that a significant hydro-climate shift occurred c. 2500 years ago, leading to the summer drought events that are critical for fires becoming more frequent.

Movement of the mean position of the polar front between middle to late Holocene has been suggested based on analyses of terrestrial pollen and marine dinocyst sequences from east Canada (Sawada et al. 1999). Rises in lake level since c. 4000 years ago (Lavoie & Richard 2000a) and of peat accumulation since c. 2000 years (Lavoie & Richard 2000b) suggest that increased prevalence of Arctic air masses has led to more annual precipitation, less evaporation and lower summer temperatures. The higher fire occurrence since c. 2500 years ago, however, suggests more frequent incursions of Pacific air at least during the vegetative season, progressively from the north of our study area. This, together with the increased variability of lake-salinity in the northern Great Plains (Laird et al. 1996), indicates that the climate has become much less stable.

Additional high-resolution lacustrine charcoal analyses over the Holocene are needed to determine the precise timing and the correlation between spatial heterogeneity of change in fire frequency and fluctuations in regional or subcontinental water balance. The mid-Holocene, between c. 7000–2500 cal. years BP, had a relatively stable climate that was less conducive to fire than the late Holocene. Climate 6000 years ago has been proposed as an analogue for that at the end of the 21st century (COHMAP Members 1988) and it should be borne in mind that the future warmer climate is likely to be less favourable for fire ignition and spread in the east Canadian boreal forest than over the last 2 millennia. This is supported by increasing fire cycles in the east boreal forest between 48° N and 50° N since ad 1850 (Bergeron et al. 2001) as the moisture index has increased (Bergeron & Archambault 1993). As the climate warms, it will become difficult to justify the current high frequency of clear-cutting as a means of emulating natural disturbance regimes.


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References

Financial support was provided by the Natural Sciences and Engineering Research Council of Canada, programme entitled ‘Networks of Centres of Excellence in Sustainable Forest Management’, and by postdoctoral grants from the Ministère de l’Éducation (Québec) and from La Fondation de l’Université du Québec à Montréal (to C.C.). We thank F. Conciatori, A.C. Larouche, N. Morasse, M. Savard and A. Wolfe for field or laboratory assistance, and M. Courcelle for discussion on 210Pb methodologies.


  1. Top of page
  2. Summary
  3. Introduction
  4. Study site
  5. Methods
  6. Results
  7. Discussion
  8. Acknowledgements
  9. References
  • Anderson, R.S., Davis, R.B., Miller, N.G. & Stuckenrath, R. (1986) History of late- and post-glacial vegetation and disturbance around Upper South Branch Pond, northern Maine. Canadian Journal of Botany, 64, 19771986.
  • Barber, D.C., Dyke, A., Hillaire-Marcel, C., Jennings, A.E., Andrews, J.T., Kerwin, M.W., Bilodeau, G., McNeely, R., Southon, J., Morehead, M.D. & Gagnon, J.-M. (1999) Forcing of the cold event of 8200 years ago by catastrophic drainage of Laurentide lakes. Nature, 400, 344348.
  • Bergeron, Y. (1991) The influence of island and mainland lakeshore landscape on boreal forest fire regime. Ecology, 72, 19801992.
  • Bergeron, Y. (2000) Species and stand dynamics in the mixed woods of Quebec's southern boreal forest. Ecology, 81, 15001516.
  • Bergeron, Y. & Archambault, S. (1993) Decreasing frequency of forest fires in the southern boreal zone of Québec and its relation to global warming since the end of the ‘Little Ice Age’. The Holocene, 3, 255259.
  • Bergeron, Y. & Brisson, J. (1990) Fire regime in red pine stands at the northern limit of the species’ range. Ecology, 71, 13521364.
  • Bergeron, Y. & Flannigan, M.D. (1995) Predicting the effects of climate change on fire frequency in the southeastern Canadian boreal forest. Water, Air, and Soil Pollution, 82, 437444.
  • Bergeron, Y., Gauthier, S., Kafka, V., Lefort, P. & Lesieur, D. (2001) Natural fire frequency for the eastern Canadian boreal forest: consequences for sustainable forestry. Canadian Journal of Forest Research, 31, 384391.
  • Bergeron, Y., Leduc, A. & Li, T.-X. (1997) Explaining the distribution of Pinus spp. in a Canadian boreal insular landscape. Journal of Vegetation Science, 8, 3744.
  • Bergeron, Y., Richard, P.J.H., Carcaillet, C., Gauthier, S., Flannigan, M. & Prairie, Y.T. (1998) Variability in fire frequency and forest composition in Canada's southeastern Boreal forest: a challenge for sustainable forest management. Conservation Ecology, 2 (6), art. 6 (
  • Carcaillet, C., Bouvier, M., Fréchette, B., Larouche, A.C. & Richard, P.J.H. (2001) Comparison of pollen-slide and sieving methods for lacustrine charcoal analyses for local and regional fire history. The Holocene, 11 (6), 467476.
  • Carcaillet, C. & Richard, P.J.H. (2000) Holocene changes in seasonal precipitation highlighted by fire incidence in eastern Canada. Climate Dynamics, 16, 549559.
  • Clark, J.S. (1988) Effects of climate change on fire regimes in northwestern Minnesota. Nature, 334, 233235.
  • Clark, J.S. (1989) Ecological disturbance as a renewal process: theory and application to fire history. Oikos, 56, 1730.
  • Clark, J.S. (1990) Fire and climate change during the last 750 yr in northern Minnesota. Ecological Monographs, 60, 135159.
  • Clark, J.S., Hussey, T. & Royall, P.D. (1996a) Presettlement analogs for Quaternary fire regimes in eastern North America. Journal of Paleolimnology, 16, 7996.
  • Clark, J.S., Lynch, J., Stocks, B.J. & Goldammer, J.G. (1998) Relationships between charcoal particles in air sediments in west-central Siberia. The Holocene, 8, 1929.
  • Clark, J.S. & Royall, P.D. (1996) Local and regional sediment charcoal evidence for fire regimes in presettlement north-eastern North America. Journal of Ecology, 84, 365382.
  • Clark, J.S., Royall, P.D. & Chumbley, C. (1996b) The role of fire during climate change in an eastern deciduous forest at Devil's Bathtub, New-York. Ecology, 77, 21482166.
  • COHMAP Members (1988) Climatic changes of the last 18 000 years: observations and model simulations. Science, 241, 10421052.
  • Cwynar, L.C. (1977) Recent history of fire of Barrow Town-ship, Algonquin Park. Canadian Journal of Botany, 55, 1021.
  • Cwynar, L.C. (1978) Recent history of fire and vegetation from laminated sediment of Greenleaf Lake, Algonquin Park, Ontario. Canadian Journal of Botany, 56, 1021.
  • Cyr, D., Bergeron, Y., Gauthier, S. & Larouche, A.C. (2000) The place of old-growth forests in the fire regulated boreal landscape. Proceedings of Disturbances Dynamics in Boreal Forests, Restoration and Management of Biodiversity (eds L.Karjalainen & T. Kuuluvainen), p. 64. Kuhmo, Finland.
  • Dansereau, P.-R. & Bergeron, Y. (1993) Fire history in the southern boreal forest of northwestern Quebec. Canadian Journal of Forest Research, 23, 2532.
  • Delong, S.C. & Tanner, D. (1996) Managing the pattern of forest harvest: lessons from wildfire. Biodiversity and Conservation, 5, 11911205.
  • Earle, C.J., Brubaker, L.B. & Anderson, P.M. (1996) Charcoal in northcentral Alaskan lake sediments: relationships to fire and Late-Quaternary vegetation history. Review of Palaeobotany and Palynology, 92, 8395.
  • Edwards, T.W.D., Wolfe, B.B. & MacDonald, G.M. (1996) Influence of changing atmospheric circulation on precipitation δ18O-temperature relations in Canada during the Holocene. Quaternary Research, 46, 211218.
  • Fægri, K., Kaland P.E. & Krzywinski K. (1989) Textbook of Pollen Analysis, 4th edn. John Wiley & Sons, London, UK.
  • Filion, L., Saint-Laurent, D., Desponts, M. & Payette, S. (1991) The Late Holocene record of aeolian and fire activity in northern Québec, Canada. The Holocene, 1, 201208.
  • Flannigan, M.D., Bergeron, Y., Engelmark, O. & Wotton, B.M. (1998) Future wildfire in circumboreal forests in relation to global warming. Journal of Vegetation Science, 9, 469476.
  • Flannigan, M., Campbell, I., Wotton, M., Carcaillet, C., Richard, P. & Bergeron, Y. (2001) Future fire in Canada's boreal forest: palaeoecology results and general circulation model – regional circulation model simulations. Canadian Journal of Forest Research, 31, 854864.
  • Flannigan, M.D. & Harrington, J.B. (1988) A study of the relation of meteorological variables to monthly provincial area burned by wildfires in Canada. Journal of Applied Meteorology, 27, 441452.
  • Flannigan, M.D. & Van Wagner, C.E. (1991) Climate change and wildfire in Canada. Canadian Journal of Forest Research, 21, 6672.
  • Flannigan, M.D. & Wotton, B.M. (1991) Lightning-ignited forest fires in northwestern Ontario. Canadian Journal of Forest Research, 21, 277287.
  • Foster, D.R. (1983) The history and pattern of fire in the boreal forest of southeastern Labrador. Canadian Journal of Botany, 61, 24592471.
  • Fuller, J. (1997) Holocene forest dynamics in southern Ontario, Canada: fine resolution pollen data. Canadian Journal of Botany, 75, 17141727.
  • Gajewski, K., Garralla, S. & Milot-Roy, V. (1996) Postglacial vegetation at the northern limit of lichen woodland in northwestern Québec. Géographie Physique et Quaternaire, 50, 341350.
  • Gajewski, K., Payette, S. & Ritchie, J.C. (1993) Holocene vegetation history at the boreal-forest – shrub-tundra transition in north-western Québec. Journal of Ecology, 81, 433443.
  • Garralla, S. & Gajewski, K. (1992) Holocene vegetation history of the boreal forest near Chibougamau, central Quebec. Canadian Journal of Botany, 70, 13641368.
  • Gauthier, S., De Grandpré, L. & Bergeron, Y. (2000) Differences in forest composition in two boreal forest ecoregions of Québec. Journal of Vegetation Science, 11, 781790.
  • Green, D.G. (1982) Fire and stability in the postglacial forests of southwest Nova-Scotia. Journal of Biogeography, 9, 2940.
  • Guiot, J. & Goeury, C. (1996) PPPBase, a software for statistical analysis of paleoecological and palaeoclimatological data. Dendrochronologia, 14, 295300.
  • Harrington, J. & Flannigan, M. (1993) A model for the frequency of long periods of drought at forested stations in Canada. Journal of Applied Meteorology, 32, 17081716.
  • Harrison, S.P. (1989) Lake levels and climatic change in eastern North America. Climate Dynamics, 3, 157167.
  • Hély, C., Bergeron, Y. & Flannigan, M.D. (2000a) Effects of stand composition on fire hazard in the mixed-wood Canadian boreal forest. Journal of Vegetation Science, 11, 813824.
  • Hély, C., Bergeron, Y. & Flannigan, M.D. (2000b) Coarse woody debris in the southeastern Canadian boreal forest: composition and load variations in relation to stand replacement. Canadian Journal of Forest Research, 30, 674687.
  • Hörnberg, G., Öslund, L., Zackrisson, O. & Bergman, I. (1999) The genesis of two Picea-Cladina forest in northern Sweden. Journal of Ecology, 87, 800814.
  • Jacobson, G.L. Jr & Bradshaw, R.H.W. (1981) The selection of sites for paleovegetational studies. Quaternary Research, 16, 8096.
  • Johnson, E.A. (1992) Fire and Vegetation Dynamics: Studies from the North American Boreal Forest. Cambridge University Press, Cambridge, UK.
  • Johnson, E.A., Fryer, G.I. & Heathcott, J.M. (1990) The influence of Man and climate on frequency of fire in the interior wet belt forest, British Columbia. Journal of Ecology, 78, 403412.
  • Johnson, E.A. & Gutsell, S.L. (1994) Fire frequency models, methods and interpretations. Advances in Ecological Research, 25, 239287.
  • Johnson, E.A., Miyanishi, K. & Weir, J.M.H. (1998) Wildfires in the western Canadian boreal forest: landscape patterns and ecosystem management. Journal of Vegetation Science, 9, 603610.
  • Koff, T., Punning, J.-M. & Kangur, M. (2000) Impact of forest disturbance on the pollen influx in lake sediments during the last century. Review of Palaeobotany and Palynology, 111, 1929.
  • Kutzbach, J., Gallimore, R., Harrison, S., Behling, P., Selin, R. & Laarif, F. (1998) Climate and biome simulations for the past 21 000 years. Quaternary Science Reviews, 17, 473506.
  • Laird, K.R., Fritz, S.C., Grimm, E.C. & Mueller, P.G. (1996) Century-scale paleoclimatic reconstructions from Moon Lake, a closed-basin lake in the northern Great Plains. Limnology and Oceanography, 41, 890902.
  • Larsen, C.P.S. (1997) Spatial and temporal variations in boreal forest fire frequency in northern Alberta. Journal of Biogeography, 24, 663673.
  • Larsen, C.P.S. & MacDonald, G.M. (1998) An 840-year record of fire and vegetation in a boreal white spruce forest. Ecology, 79, 106118.
  • Lavoie, M. & Richard, P.J.H. (2000a) Postglacial water-level changes of a small lake in southern Quebec, Canada. The Holocene, 10, 621634.
  • Lavoie, M. & Richard, P.J.H. (2000b) The role of climate on the developmental history of Frontenac peatland, southern Québec. Canadian Journal of Botany, 78, 668684.
  • Liu, K.-B. (1990) Holocene paleoecology of the boreal forest and Great Lakes-St. Lawrence forest in northern Ontario. Ecological Monograph, 60, 179212.
  • Long, C.J., Whitlock, C., Bartlein, P.J. & Millspaugh, S.H. (1998) 9000-year fire history from the Oregon Coast range, based on a high-resolution charcoal study. Canadian Journal of Forest Research, 28, 774787.
  • Mehringer, P.J. Jr, Arno, S.F. & Petersen, K.L. (1977) Postglacial history of Lost Trail Pass bog, Bitterroot mountains, Montana. Arctic and Alpine Research, 9, 345368.
  • Millspaugh, S.H. & Whitlock, C. (1995) A 750-year fire history based on lake sediment records in central Yellowstone National Park, USA. The Holocene, 5, 283292.
  • Millspaugh, S.H., Whitlock, C. & Bartlein, P.J. (2000) Variations in fire frequency and climate over the past 17 000 yr in central Yellowstone National Park. Geology, 28, 211214.
  • Nash, C.H. & Johnson, E.A. (1996) Synoptic climatology of lightning-caused forest fires in subalpine and boreal forests. Canadian Journal of Forest Research, 26, 18591874.
  • Ohlson, M. & Tryterud, E. (2000) Interpretation of the charcoal record in forest soils: forest fires and their production and deposition of macroscopic charcoal. The Holocene, 10, 519525.
  • Payette, S. & Filion, L. (1993) Holocene water-level fluctuations of a subarctic lake at the treeline in northern Québec. Boreas, 22, 714.
  • Payette, S. & Lavoie, C. (1994) The arctic tree line as a record of past and recent climatic changes. Environmental Reviews, 2, 7890.
  • Phillips, D. (1990) The Climates of Canada. Environment Canada, Ottawa, Ontario, Canada.
  • Rhodes, T.E. & Davis, R.B. (1995) Effects of late Holocene forest disturbance and vegetation change on acidic mud pond, Maine, USA. Ecology, 76, 734746.
  • Richard, P.J.H. (1980) Histoire postglaciaire de la végétation au sud du lac Abitibi, Ontario et Québec. Géographie Physique et Quaternaire, 34, 7794.
  • Rowe, J.S. & Scotter, G.W. (1973) Fire in the boreal forest. Quaternary Research, 3, 444464.
  • Sawada, M., Gajewski, K., De Vernal, A. & Richard, P.J.H. (1999) Comparison of marine and terrestrial Holocene climatic reconstructions from north-eastern North America. The Holocene, 9, 267277.
  • Stocks, B.J., Fosberg, M.A., Lynham, T.J., Mearns, L., Wotton, B.M., Yang, Q., Jin, J.-Z., Lawrence, K., Hartley, G.R., Mason, J.A. & McKenney, D.W. (1998) Climate change and forest fire potential in Russian and Canadian boreal forest. Climatic Change, 38, 113.
  • Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, F.G., Van Der Plicht, J. & Spurk, M. (1998) INTCAL98 Radiocarbon Age Calibration, 24,000–0 cal BP. Radiocarbon, 40, 10411083.
  • Terasmae, J. & Anderson, T.W. (1970) Hypsitermal range extension of white pine (Pinus strobus L.) in Québec, Canada. Canadian Journal of Earth Sciences, 7, 406413.
  • Tinner, W., Conedera, M., Ammann, B., Gäggeler, H.W., Gedye, S., Jones, R. & Sägesser, B. (1998) Pollen and charcoal in lake sediments compared with historically documented forest fires in southern Switzerland since ad 1920. The Holocene, 8, 3142.
  • Tinner, W., Hubschmid, P., Wehrli, M., Ammann, B. & Conedera, M. (1999) Long-term forest fire ecology and dynamics in southern Switzerland. Journal of Ecology, 87, 273289.
  • Van Wagner, C.E. (1978) Age-class distribution and the forest fire cycle. Canadian Journal of Forest Research, 8, 220227.
  • Veillette, J.J. (1994) Evolution and palaeohydrology of glacial lakes Barlow and Ojibway. Quaternary Science Reviews, 13, 945971.
  • Vincent, J.-S. (1973) A palynological study for the Little Clay Belt, northwestern Québec. Le Naturaliste Canadien, 100, 5970.
  • Wein, R.W., Burzinski, M.P., Sreenivasa, B.A. & Tolonen, K. (1987) Bog profile evidence of fire and vegetation dynamics since 3000 years BP in the Acadian forest. Canadian Journal of Botany, 65, 11801186.
  • Weir, J.M.H., Johnson, E.A. & Miyanishi, K. (2000) Fire frequency and the spatial age mosaic of the mixed-wood boreal forest in western Canada. Ecological Applications, 10, 11621177.
  • Whitlock, C. & Millspaugh, S.H. (1996) Testing the assumptions of fire-history studies: an examination of modern charcoal accumulation in Yellowstone National Park, USA. The Holocene, 6, 715.
  • Wotton, B.M. & Flannigan, M.D. (1993) Length of the fire season in a changing climate. Forestry Chronicle, 69, 187192.
  • Yu, Z., McAndrews, J.H. & Eicher, U. (1997) Middle Holocene dry climate caused by change in atmospheric circulation patterns: evidence from lake levels and stable isotopes. Geology, 25, 251254.