# Fire-controlled variations in abundance of white pine and red pine in Quebec's northern temperate forest during the Holocene: Implications for fire management

Marion Blache, Adam Ali, Dorian Gaboriau, Sébastien Joannin, Mathis

Jean-Sepet, Martin Girardin, Yves Bergeron, Hugo Asselin

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

Marion Blache, Adam Ali, Dorian Gaboriau, Sébastien Joannin, Mathis Jean-Sepet, et al.. Fire-controlled variations in abundance of white pine and red pine in Quebec's northern temperate forest during the Holocene: Implications for fire management. The Holocene, 2025, 36 (1), pp.28-36. 10.1177/09596836251378033. hal-05331799

HAL Id: hal-05331799

https://hal.science/hal-05331799v1

Submitted on 2 Mar 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
1 Fire-controlled variations in abundance of white pine and red pine in Quebec's northern

2 temperate forest during the Holocene: implications for fire management

3 Marion Blache¹,², Adam A. Ali¹, Dorian M. Gaboriau², Sébastien Joannin¹, Mathis Jean-

4 Sepet¹,², Martin P. Girardin³, Yves Bergeron²,⁴, Hugo Asselin⁵

5

6 1. ISEM, Université de Montpellier, CNRS, IRD, Montpellier, France

7 2. Institut de recherche sur les forêts, Université du Québec en Abitibi-Témiscamingue, 445

8 boulevard de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada

9 3. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, Quebec
10 City, QC, Canada

10

11 4. Département des sciences biologiques, Université du Québec à Montréal, case postale 8888

12 succursale centre-ville, Montréal, QC, H3C 3P8, Canada

13 5. École d'études autochtones, Université du Québec en Abitibi-Témiscamingue, 445

14 boulevard de l'Université, Rouyn-Noranda, QC, J9X 5E4, Canada

15

16 ORCID

17 Adam A. Ali: https://orcid.org/0000-0002-6927-6633

18 Dorian M. Gaboriau: https://orcid.org/0000-0002-1967-3710

19 Sébastien Joannin: https://orcid.org/0000-0001-8345-9252

20 Martin P. Girardin: https://orcid.org/0000-0003-0436-7486

21 Yves Bergeron: https://orcid.org/0000-0003-3707-3687

22 Hugo Asselin: https://orcid.org/0000-0002-9542-4994

23

24 Corresponding author :

25 Marion Blache

26 Institutional address : 445 boul de l'université, Rouyn-Noranda (QC), J9X 5E4

27 Phone : 819 443 2049

28 Email : marion.blache@uqat.ca,

29

30

31
32

**Abstract**

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

In North American temperate forests, white pine (*Pinus strobus* L.) and red pine (*Pinus resinosa* Ait.) establish on sites cleared by infrequent high-severity crown fires and persist in the long-term when low-severity surface fires clear the understory and expose mineral seedbeds, facilitating regeneration. Considerable reduction of white pine and red pine abundance over the last two centuries due to overharvesting and fire suppression prompted experiments with prescribed burning. In La Mauricie National Park (LMNP; southern Québec, Canada) all natural fires have been actively suppressed since the 1970s, and only prescribed (surface) burns occurred since the 1990s. Taking advantage of this unique setting, we quantified charcoal particles in the sediments of three lakes within LMNP to identify a tentative charcoal accumulation threshold differentiating surface fires from crown fires. We then compared the signal left by the current regime of surface fires with the fire regimes of other periods of the Holocene. Based on the threshold, we showed that a mixed regime of frequent low-severity surface fires and infrequent high-severity crown fires was associated to high abundance of white pine and red pine during the Holocene Thermal Maximum (ca. 8,400-4,500 cal. yr BP). Regimes of only surface fires during the early Neoglacial period (ca. 4,500-1,500 cal. yr BP) or only crown fires during the early Holocene (before 8,400 cal. yr BP) were less conducive to the establishment and persistence of white pine and red pine. Instead of systematically suppressing crown fires, they should be allowed to burn while protecting infrastructures.

53

**Keywords:** *Pinus strobus*; *Pinus resinosa*; fire regime; surface fire; crown fire; prescribed burn
**Introduction**

The northern temperate forests of eastern North America are shaped by numerous biotic (insect outbreaks, pathogens, gap dynamics) and abiotic (fires, windthrow) natural disturbances (Frelich, 2002; Grenier et al., 2005; Drever et al., 2006; Després et al., 2014) resulting in a mosaic of forest patches of varying composition and structure. Some temperate tree species depend on fire for their regeneration, particularly white pine (*Pinus strobus* L.) and red pine (*Pinus resinosa* Ait.) (Weyenberg et al., 2004; Nyamai et al., 2014; Abadir et al., 2019). Relatively infrequent severe crown fires with a return interval of 100 to 350 years allow white pine and red pine to colonise new sites (Engelmark et al., 2000; Stambaugh et al., 2021; Pastor, 2023), whereas frequent (every ca. 20-50 years) low-severity surface fires are necessary to clean the understory vegetation and expose the mineral soil, both conditions ensuring long-time persistence of white pine and red pine through understory regeneration (Bergeron and Gagnon, 1987; Weyenberg, 2004; Brown, 2009; Marschall et al., 2022).

The abundance of white pine reached a peak between ca. 8,000 and 4,500 cal. yr BP (calibrated years before present), i.e., during the Holocene Thermal Maximum (hereafter HTM; Terasmae and Anderson, 1970; Bennett, 1987; Larochelle et al., 2018). During that period, the distribution of white pine expanded at least 100 km further north than its current northern limit (Liu, 1990; Terasmae and Anderson, 1970; Richard, 1993). Then, during the Neoglacial period (ca. 4,500-0 cal. yr BP), the abundance of white pine decreased and its distribution receded southward (Liu, 1990; Richard, 1993; Larochelle et al., 2018). Red pine likely followed a similar trend during the Holocene, but it is difficult to ascertain because previous studies did not always differentiate its pollen grains from those of jack pine (*Pinus banksiana* Lamb.), which is a boreal species.

While climate change is likely part of the explanation for the Holocene fluctuations in the abundance and distribution of white pine and red pine (Larochelle et al., 2018; Robles et al., 2024), changes in fire regimes could have also played a role, although this hypothesis has
yet to be fully tested. According to fire regime reconstructions based on the quantification of charcoal particles embedded in lake sediments, fire occurrence was high in northern temperate forests during the early Holocene, before decreasing during the HTM, increasing during the early Neoglacial, and decreasing again over the last 1500 years (Blarquez et al., 2015, 2018; Paillard et al., 2023). These reconstructions, however, do not allow to distinguish surface fires from crown fires, which is essential to properly understand fire-vegetation dynamics in temperate red pine and white pine forests.

The La Mauricie National Park (LMNP) in south-central Québec (Canada) offers a unique setting to study fire regimes in temperate red pine and white pine stands, as the park has only been affected by prescribed burns (human-ignited controlled surface fires) since 1991. Lightning-ignited fires have been suppressed systematically to prevent the risk of high-severity crown fires, whereas prescribed burns have been conducted to facilitate the regeneration of white pine stands (Hébert et al., 2020; Montour et al., 2020). Hence, charcoal particles in the topmost sediments of lakes located near prescribed burn areas in LMNP, representing the last few decades of accumulation, would provide a surface fire signal.

We quantified charcoal particles in the sediments of three lakes in LMNP to reconstruct the Holocene fire regime. We hypothesized that white pine and red pine would be most favoured by a mixed regime of frequent low-severity surface fires and infrequent high-severity crown fires, and that regimes of only surface fires or only crown fires would be respectively less conducive to the establishment and persistence of white pine and red pine (Engstrom and Mann, 1991; Brown, 2009; Stambaugh et al., 2021; Pastor, 2023). We discuss the implications of our findings for fire management practices in white pine and red pine forests.

102
103 **Material and methods**

104 **Study area and local vegetation**

105 LMNP was created in 1977 and covers an area of 536 km² (Hébert et al., 2020). It is located in
106 the northern temperate zone of Québec (Canada), more precisely within the sugar maple (Acer
107 saccharum Marsh.) – yellow birch (Betula alleghaniensis Britt.) bioclimatic domain (Saucier et
108 al., 2010). The forests of LMNP are mainly composed of maples (Acer spp.), birches (Betula
109 spp.), as well as balsam fir (Abies balsamea (L.) Mill.), black spruce (Picea mariana (Mill)
110 B.S.P.), white pine and red pine. Some old eastern hemlock (Tsuga canadensis (L.) Carr.) trees
111 are also present (Marchand and Filion, 2014). The Shawinigan weather station (25 km south of
112 the park) recorded an average annual temperature of 4.8 °C for the period 1981–2010
113 (Environnement Canada, n.d.). Total annual precipitation for the same period was 1085.3 mm,
114 with 226 mm falling as snow.

115 During the century preceding the creation of LMNP, the abundance of white pine and
116 red pine declined in the study area – as in all northeastern North America – due to
117 overexploitation and fire suppression (Weyenberg et al., 2004; Uprety et al., 2014;
118 Danneyrolles et al., 2016; Robles et al., 2025). There are records of fire events dating back to
119 1836 in the area now corresponding to LMNP (surface and crown fires were not differentiated
120 in the record), but since the 1970s, all natural fires within the park have been suppressed as
121 soon as they appeared. Between 1991 and 2020, 22 prescribed burns were conducted within red
122 pine and white pine stands in the park (Hébert et al., 2020; Montour et al., 2020). Hence, starting
123 from the 1990s, only prescribed burns contributed to the area burned within LMNP, except for
124 one natural crown fire which temporarily escaped suppression measures in 2003, burning 385
125 ha in the northeastern part of LMNP, at least 8 km from the nearest studied lake (Pool).

126 Experiments with prescribed burning were prompted by growing awareness of the
127 negative effects of fire suppression policies on white pine and red pine populations in various
areas of northeastern North America (including LMNP). While prescribed burns were thought
to favour pine regeneration and restoration (McRae et al., 1994; Scherer et al., 2018; Schiks et
al., 2024), they did not achieve the expected results, because they have not been severe enough
to expose the mineral soil (Gagnon, 2024), but maybe also – as we hypothesized – because a
regime of only surface fires does not allow new pine stands to establish.

133

134 *Sampling design*

135 We collected sediments from three lakes (Pool, Couronne, and à Sam) with pine stands in their
136 watersheds in February 2022 (Figure 1; Table 1). To avoid bioturbation, we collected the
137 sediments from the deepest part of each lake. We used a Kajak-Brinkhurst gravity corer (Glew,
138 1991) to sample the water-sediment interface, which we subsampled in the field into 0.5-cm
139 thick slices stored in plastic bags. We collected deeper sediments, down to the underlying
140 inorganic sediments, in 1-m cores using a 5-cm diameter Livingstone corer (Deevey, 1965).
141 The cores were wrapped in plastic film and aluminium foil and placed in hemicylindrical PVC
142 tubes for transport. In the laboratory, the cores were sliced into 1-cm thick samples and placed
143 in plastic bags for storage at 4 °C.
144

144
<figure><img src="image_3.png" /></figure>

**Figure 1.** (a) Locations of the three sampled lakes in La Mauricie National Park (LMNP) as well as areas where prescribed burns were conducted since 1991, and where natural fires occurred between 1836 and 1970 (one natural fire occurred in 2003 and took longer than usual to extinguish, but only burned 385 ha, 8 km southeast of lake Pool). (b) Locations of some of the previous studies having recorded high abundance of white pine and red pine during the Holocene Thermal Maximum in Quebec and Ontario (see Supplemental Table S1).

<table><caption>**Tableau 1.** Characteristics of the three sampled lakes.</caption><thead><tr><th></th><th>Pool</th><th>Couronne</th><th>à Sam</th></tr></thead><tbody><tr><td>Latitude (°N)</td><td>46°50'38"</td><td>46°46'32"</td><td>46°39'13"</td></tr><tr><td>Longitude (°W)</td><td>72°59'23"</td><td>72°50'03"</td><td>72°58'36"</td></tr><tr><td>Surface area (ha)</td><td>3.30</td><td>3.86</td><td>2.05</td></tr><tr><td>Elevation (m a.s.l.)</td><td>288</td><td>239</td><td>225</td></tr><tr><td>Maximum water depth (m)</td><td>5.00</td><td>10.90</td><td>6.25</td></tr><tr><td>Total length of sediments collected (cm)</td><td>419</td><td>436</td><td>260</td></tr><tr><td>Sedimentation rate (cm yr<sup>-1</sup>)</td><td>0.049</td><td>0.054</td><td>0.033</td></tr><tr><td>Date of last prescribed burn</td><td>2015</td><td>2007</td><td>2015</td></tr><tr><td>Distance to prescribed burn (m)</td><td>0</td><td>300</td><td>2000</td></tr></tbody></table>
## Radiocarbon dating and age-depth models

Macro-remains from each core were dated using ¹⁴C accelerator mass spectrometry (Table S2).

We calibrated each radiocarbon date using the IntCal20 Northern Hemisphere calibration curve (Reimer et al., 2020) to obtain calibrated years before present (hereafter cal. yr BP). We used the *rbacon* package v.3.2.0 in R v.4.4.0 (R Core Team, 2024) to build Bayesian age-depth models (Blaauw and Christen, 2011). We subsequently interpolated ages of contiguous 1-cm samples.

## Charcoal quantification

We took a 1 cm³ subsample from the middle of each sediment sample to limit contamination (Mustaphi et al., 2015). To deflocculate the sediments and to distinguish charcoal particles from dark organic matter, the subsamples were placed in a potassium hydroxide (KOH) solution with bleach (NaClO) and sodium hexametaphosphate ($NaPO_3)_6$ and left on a stirring table at 130 revolutions per minute (rpm) for 24 hours at ambient temperature (Braadbaart and Poole, 2008).

We then filtered the solution through a 160-µm mesh sieve to collect charcoal particles corresponding to fires having likely occurred 0–10 km from the lakeshores (Oris et al., 2014).

The retained charcoal particles were counted and measured (mm²) under a camera (AmScope, version x64) mounted on a binocular microscope and connected to an image analysis software (WinSeedle v2022a).

## Fire history reconstruction

We used the charcoal accumulation rate (CHAR) series decomposition method (Higuera, 2009) to detect the fire events having occurred during the Holocene in LMNP based on charcoal particles embedded in the sediments of the three sampled lakes. The charcoal accumulation rate was divided into a high-frequency signal (CHAR<sub>peaks</sub>) and a low-frequency signal (CHAR<sub>background</sub>) using the open-source software CHARAnalysis
(https://sites.google.com/site/charanalysis/; Figure S1). Peaks were then identified as either fire or non-fire events based on a Gaussian mixture model (99th percentile threshold).

For each of the three lakes, we used linear interpolation of the charcoal accumulation rate (mm²·cm⁻²·yr⁻¹) to reconstruct annual biomass burned (BB) at each lake with the R *paleofire* package (version 1.2.4) (Blarquez et al., 2014). Biomass burned was rescaled using the min-max method to allow for between-lake comparisons (Power et al., 2008). The regional biomass burned (RegBB), combining the three lakes, was calculated and its confidence interval (95%) was obtained using bootstrap resampling (Ali et al., 2012).

The fire return interval (hereafter FRI), corresponding to the time between two consecutive fire events, was also computed and LOWESS smoothing was applied to the data to reconstruct long-term trends at local (individual site) and regional spatial scales (composite of the three sites). Confidence intervals (95%) were calculated for each lake's FRI values and for the regional values using bootstrap resampling.

Around the studied lakes, fires from the last 30 years were all prescribed burns, as natural fires have been suppressed. To identify a surface fire signal (to be compared with signals reconstructed during the rest of the Holocene), we used the maximum charcoal accumulation rate in the topmost 10 centimetres of the surface cores, thought to correspond to the last ca. 50 years of sediment accumulation based on ²¹⁰Pb dating from previous studies conducted in Quebec's northern temperate forest: one within LMNP (Bérubé Tellier et al. 2016) and two 200-450 km to the west (Paquette and Gajewski, 2013; Paillard et al., 2023).

## Pollen analysis

To reconstruct vegetation dynamics in LMNP, we used raw data from a previous analysis of the pollen grains retrieved from a 425-cm long sediment core collected from lake à Sam in 1975 (Pierre J.H. Richard, unpublished data; Figure S2). Pollen grains had been counted
at depth intervals ranging from 5 to 15 cm, for a total of 53 samples, with a minimum of 500 grains counted per sample, and differentiating pollen grains from red pine and jack pine (Pierre J.H. Richard, unpublished data). Using these raw data, we transformed pollen counts into percentages, and we calculated the pollen influx (PI) using the following formula (Hicks and Hyvärinen, 1999):

$$PI = SR*PC$$

where SR is the sedimentation rate (cm·yr⁻¹) deduced from the age-depth model, and PC is the pollen concentration (grains·cm⁻³) (Jørgensen, 1967).

We produced pollen diagrams with the R package rioja v1-0-6 (Figure S2). Pollen zones were determined using cluster analysis (constrained incremental sum-of-squares method; CONISS) applied to the relative pollen abundance of *Pinus* spp. using the Bray-Curtis index for the calculation of the distance matrix.

Because the climate of the study area has fluctuated during the Holocene, including periods when it was cooler than it is presently, we calculated a temperate/boreal species ratio (based on pollen percentages), to verify if LMNP was temperate or boreal at any given time. To do so, we used the two main boreal tree taxa as the numerator (*Pinus banksiana* and *Picea mariana*) and four characteristic temperate taxa as the denominator (*Acer saccharum*, *Pinus strobus*, *Pinus resinosa*, and *Tsuga canadensis*). As the pollen grains from *Betula papyrifera* Marsh. (boreal) and *Betula alleghaniensis* (temperate) are difficult to distinguish, they were not used in the calculation of the ratio.

## Results

### Age-depth models

The sampled cores were all composed of gyttja with clay underneath. The gyttja-clay transition occurred at lake Pool between 403 and 411 cm, at lake Couronne between 429 and 438 cm, and
233

at lake à Sam between 237 and 241 cm. The age-depth models were based on eight radiocarbon dates for lake Pool and lake Couronne, and five radiocarbon dates for lake à Sam (Table S2).

234

235

The oldest ages of sediments found at each study site were 9,642 cal. yr BP at lake Pool, 10,041 cal. yr BP at lake Couronne, and 13,158 cal. yr BP at lake à Sam (Figure 2). The sedimentation rate was relatively constant for the three lakes during the Holocene.

236

237

238

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

239

**Figure 2.** Age-depth models for (a) Lake Pool, (b) Lake Couronne, and (c) Lake à Sam, obtained from rbacon v.3.2.0 using the 14C dates listed in Supplemental Table S2.

240

241

242

## Determination of the surface fire signal

243

To detect the CHAR signal left by prescribed burns, we considered the uppermost 10 cm of sediments from the cores sampled with the Kajak-Brinkhurst corer.

244

245
Only lakes Pool and Couronne contained charcoal particles in the top 10 cm of sediments, because they had prescribed burns nearby (< 300 m), whereas lake à Sam was 2 km from the nearest prescribed burn. The CHAR values were low (< 0.1 mm²·cm⁻²·yr⁻¹) throughout the uppermost 10 cm at lake Pool, and 7.5 cm at lake Couronne (Figure 3). CHAR values from 8 cm and below at lake Couronne were much higher (reaching > 0.3 mm²·cm⁻²·yr⁻¹ at 8.5 cm depth) and clearly represented crown fires having occurred before the fire suppression policy was introduced in the 1970s. The maximum CHAR value of the uppermost 7.5 cm (bot lakes considered) was 0.058 mm²·cm⁻²·yr⁻¹ and was thus selected as the surface fire signal.

<figure><img src="image_6.png" /></figure>

**Figure 3.** Charcoal accumulation rates recorded in the uppermost 10 cm of sediments from lake Pool (green) and lake Couronne (blue; lake à Sam did not have charcoal within the top 10 cm). The horizontal dashed line corresponds to the surface fire signal, that is, the maximum charcoal accumulation rate (0.058 mm²·cm⁻²·yr⁻¹) of the period when only surface fires (prescribed burns) occurred in the study area.
Only the uppermost 7.5 cm were considered to identify the threshold, as from 8 cm and below, very high charcoal concentrations at lake Couronne are clearly indicative of crown fires having occurred before the fire suppression policy was introduced in the 1970s.

264

## Biomass burned during the Holocene

Biomass burned estimated from the charcoal accumulation rate can be divided into three periods at lake Pool. Charcoal accumulation rates were highest in the early Holocene with a maximum value of 1.4 mm²·cm⁻²·yr⁻¹, intermediate and variable during the HTM, and lowest during the Neoglacial with values below 0.1 mm²·cm⁻²·yr⁻¹ (Figure 4a). A total of 57 fire events were identified over the Holocene, 39 of which displayed CHAR values below the threshold differentiating surface fires from crown fires (0.058 mm²·cm⁻²·yr⁻¹), mostly during the Neoglacial.

267

268

269

270

271

272

273
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Holocene biomass burned based on charcoal accumulation rates at (a) lake Pool, (b) lake Couronne and (c) lake à Sam. The horizontal red dashed line corresponds to the threshold value (0.058 mm²·cm⁻²·yr⁻¹) differentiating surface from crown fires. The red crosses represent high-severity crown fires, and the green crosses represent low-severity surface fires.</figcaption></figure>

Biomass burned at lake Couronne was highest during the early Holocene with charcoal accumulation rates reaching up to 0.9 mm²·cm⁻²·yr⁻¹ (Figure 4b). During the HTM, charcoal accumulation rates were intermediate and variable. The lowest accumulation rates were recorded during the early Neoglacial, below 0.05 mm²·cm⁻²·yr⁻¹.
Then, biomass burned increased during the last 1,000 cal. yr BP, reaching 0.3 mm²·cm⁻²·yr⁻¹.

A total of 49 fire events were identified over the Holocene, 31 of which displayed CHAR values below the threshold, mostly during the Neoglacial.

At lake à Sam, biomass burned was lower than at the other two sites, almost always below 0.05 mm²·cm⁻²·yr⁻¹ (Figure 4c). Three periods had markedly higher CHAR values: around 9,800 cal. yr BP, around 8,200 cal. yr BP, and between 5,900 and 5,000 cal. yr BP. A total of 23 fires were identified, 20 of which displayed CHAR values below the threshold, distributed throughout the Holocene.

292

## Fire return interval

At the regional scale, the mean FRI (FRIm) during the Holocene was 229 years, with lower values in the early Holocene and early Neoglacial periods, although the confidence intervals overlap (Figure 5). The three studied lakes followed similar trends, although FRI values for Lake à Sam were about twice higher than at the other two lakes. FRI values were lower during the early Holocene (mostly below the long-term mean between 10,000 and 8,500 cal. yr BP), higher during the HTM (mostly above the long-term mean between 8,500 and 4,000 cal. yr BP at lake Pool and between 8,500 and 5,000 cal. yr BP at lake Couronne), then decreasing in the early Neoglacial (around or below the long-term mean up to about 1,000 cal. yr BP), and finally increasing again in the most recent millennium (above the long-term mean).

294

295

296

297

298

299

300

301

302

303
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Holocene variations of the fire return interval (FRI) at the regional scale (a) and at lakes Pool (green), Couronne (blue) and à Sam (orange; b). The shaded areas represent the 95% confidence intervals. The horizontal red dashed line represents the average regional FRI for the Holocene.</figcaption></figure>
309 **Pine dynamics during the Holocene**

310 Three pine pollen zones (PPZ) were reconstructed based on the CONISS analysis (Figure 6).
311 The first zone (PPZ1: 9,600-8,400 cal. yr BP) was characterised by a high proportion (30%) of
312 boreal taxa, notably jack pine (Figure S2). The relative abundance of white pine started to
313 increase at the end of PPZ1, from 5% to 20%. Red pine was also present but at low relative
314 abundance (< 2%). The second zone (PPZ2; 8,400-6,700 cal. yr BP) was dominated by white
315 pine, which reached almost 40%, while jack pine and red pine were lower (respectively 10%
316 and 4%). During this period, the abundance of boreal taxa decreased markedly. In the third zone
317 (PPZ3; 6,700-0 cal. yr BP), the relative abundance of white pine decreased by half, but it
318 remained more abundant than the other two pine taxa. Red pine's relative abundance peaked
319 between 5,000 and 4,000 cal. yr BP, reaching 5%.

320

321

322 **Discussion**

323 **Fire regimes and pine dynamics**

324 The early Holocene (PPZ1: 10,000-8,400 cal. yr BP) in LMNP was characterized by the
325 dominance of jack pine, under a regime of frequent (low FRI values), likely high-severity fires
326 (high biomass burning). Because charcoal accumulation rates are positively correlated with fire
327 severity (Hennebelle et al., 2020) the fact that the early Holocene recorded the highest CHAR
328 values of the Holocene at lakes Pool and Couronne is a clear indication that crown fires
329 dominated. Moreover, jack pine is a shade-intolerant species whose regeneration depends on
330 high-severity crown fires to open its serotinous cones (Asselin et al., 2003; Smirnova et al.,
331 2008). As we hypothesized, the early-Holocene fire regime, dominated by crown fires with few
332 surface fires, was not favourable to white pine and red pine.
<figure><img src="image_9.png" /><figcaption>**Figure 6.** Regional biomass burned (mm²·cm⁻²·yr⁻¹) and regional fire return interval (years) from 9600 cal. yr BP to the present, plotted alongside the abundance (percentage) of pollen grains of *Pinus banksiana*, *Pinus resinosa*, and *Pinus strobus*. Total pollen influx is also shown (grains·cm⁻²·yr⁻¹), as well as the ratio of key temperate to boreal taxa. Three pine pollen zones (PPZ) were identified from the CONISS analysis.</figcaption></figure>
337

Then, during the HTM (PPZ2 and beginning of PPZ3: 8,400-4,500 cal. yr BP), dominance switched from jack pine to white pine, with red pine also present although probably at lower abundance. At that time, regional biomass burning was lower and FRI values were higher than during the early Holocene, and both components of the fire regime showed great variability. The fire regime was a mix of frequent low-severity surface fires and infrequent high-severity crown fires. Some of the surface fires were likely ignited by Indigenous people who used prescribed burns to increase berry production (e.g., Vaccinium spp.), create habitats for wildlife species (e.g., *Alces americanus*, *Lepus americanus*), and to reduce the risk of crown fires (Christianson et al., 2022). As we hypothesized, the mixed fire regime was well suited to the development and persistence of white pine and red pine (Engstrom and Mann, 1991; Brown, 2009; Stambaugh et al., 2021; Pastor, 2023). It is during the warmer HTM that the temperate species gradually colonized the study area, with fire-adapted species coming first (e.g., *Pinus strobus*, *Pinus resinosa*, *Quercus* spp.) followed by other typical temperate species (e.g., *Acer saccharum* Marsh., *Fagus grandifolia* Ehr., *Betula alleghaniensis* Britt., *Tsuga canadensis* (L.) Carr.).

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

The onset of the cool Neoglacial period around 4,500 cal. yr BP coincided with a decrease in the abundance of white pine and red pine in LMNP, as elsewhere in Québec (Richard, 1993; Larochelle et al., 2018), although they remained more abundant than during the early Holocene. The fire regime was characterized by the lowest values of biomass burning and by low FRI values, likely because of the increased presence of deciduous hardwood taxa not prone to burning (e.g., *Acer*, *Fagus*, *Betula*). Most of the fire events corresponding to the surface fire signal occurred during the Neoglacial. Again, this finding corroborates our hypothesis that a fire regime with only surface fires would not be favourable to white pine and red pine. The species decreased in abundance, but remained present, because surface fires created favourable
seedbeds for some stands to regenerate, but lack of crown fires prevented new sites from being colonized (Engelmark et al., 2000; Stambaugh et al., 2021; Pastor, 2023).

Over the last 1000 years, biomass burning and FRI increased again, maybe in response to warmer and drier conditions during the Medieval Warm Period (Paquette and Gajewski, 2013) and recent climate warming. The alternance of frequent low-severity surface fires and infrequent high-severity crown fires resumed. It is during that time that the white pine and red pine forests logged by the first European settlers in the 19th century were established (Brisson and Bouchard, 2003; Clifford and Castonguay, 2022). Then, because of overexploitation and active fire suppression during the last few decades, white pine and red pine declined in most temperate Quebec (Weyenberg et al., 2004; Uprety et al., 2014; Danneyrolles et al., 2016), including the LMNP, where the regime of only surface fires (prescribed burns) allows to maintain some pine populations, but not to create new ones.

While our vegetation reconstruction relied on a single site, it is well-known that the pollen rain at a lake has both a local and a regional component (Davis, 2000). The general trends we observed in the abundance of the three pine species (jack, white, red) and other tree species correspond with the Holocene vegetation history of Quebec's northern temperate forests (Richard et al., 2025).

The fire history at lake à Sam differs from those at lakes Pool and Couronne in that it was largely dominated by low-severity surface fires, with only three crown fire events recorded in the early Holocene (1) and during the HTM (2). This could be due to local site conditions (e.g., topography, comparatively smaller watershed). Nevertheless, the general trends observed in terms of biomass burning and FRI were consistent with those at the other sites.

### Detection of surface fires in lake sediments: insight and limitations

The unique setting of LMNP, with only surface fires (prescribed burns) having occurred over the last 30 years, allowed us to identify a charcoal accumulation rate threshold below which
fires could reasonably be considered as surface fires. This threshold (0.058 mm²·cm⁻²·yr⁻¹) is
likely perfectible and more studies should be conducted to refine it and to determine if it is
region-specific or if it applies more broadly. For example, traps could be installed at lake surface
or on the ground nearby to collect charcoal during wildfires and prescribed burns (e.g., Lynch
et al., 2004; Oris et al., 2014; Hennebelle et al., 2020). In addition, more precise chronological
markers (e.g., ¹³⁷Cs and ²¹⁰Pb) could be used to more accurately date the surface sediments.
Nevertheless, the threshold seems acceptable as, by way of comparison, in coniferous boreal
forests mainly affected by high-severity crown fires, CHAR values are well above 0.1 mm²·cm⁻¹
²·yr⁻¹ (e.g., Ali et al., 2008, 2009). Hence, the odds of wrongfully identifying a crown fire as a
surface fire (and vice versa) are very low.

397

## Conclusion

We introduced a charcoal accumulation rate threshold to differentiate surface fires from crown
fires in lake sediment-based fire history reconstructions in temperate forest ecosystems. The
Holocene fire and vegetation histories we reconstructed for three sites in La Mauricie National
Park (Québec, Canada) suggest, in line with our hypothesis, that white pine and red pine are
most favoured by a mixed regime of frequent low-severity surface fires and infrequent high-
severity crown fires, and that regimes of only surface fires or only crown fires are respectively
less conducive to the establishment and persistence of white pine and red pine.

The regime of only surface fires in place at LMNP since 1991 differs from the mixed
regime of frequent low-severity surface fires and infrequent high-severity crown fires which
could be considered “ideal” for white pine and red pine establishment and persistence.
Prescribed burns should be severe enough to expose the mineral soil and favour pine
regeneration (Gagnon, 2024). Moreover, instead of systematically suppressing natural crown
fires, they should be allowed to burn while increasing preparedness to protect infrastructures
and reduce their vulnerability (Tymstra et al., 2020).

413

414 Acknowledgements

We would like to thank Kim Charron-Charbonneau and Mathieu St-Laurent-Addison for
providing us with the archives concerning the fires in La Maurie National Park. We are grateful
to Marc-André Lamothe (LMNP), Raynald Julien (UQAT), David Gervais (Canadian Forest
Service - CFS) and Mathieu Gauvin (CFS) for their help during fieldwork. Thanks also to
professor Pierre J.H. Richard for providing the detailed pollen diagram of lake à Sam and for
his comments on an earlier version of the manuscript.

421

422 Declaration of conflicting interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

425

426 Funding statement

This project received financial support from La Mauricie National Park and an Alliance grant
from the Natural Sciences and Engineering Research Council of Canada (NSERC; grant #
ALLRP 572229 - 22). This article is a contribution of the Cold Forests International Research
Network, funded by the Fonds de recherche du Québec - Nature et technologie (FRQNT) and
the Centre national de la recherche scientifique (CNRS).

432

433 Ethical approval and informed consent statements

This article does not contain any studies with human or animal participants.

There are no human participants in this article and informed consent is not required.
436 **sData availability statement**

437 The data that support the findings of this study are available from the corresponding author, M.

438 B, upon reasonable request.

439 **Supplemental material**

440 Supplemental material for this article is available online.

441

442 **References**

443 Abadir ER, Marschall JM, Dey DC et al. (2019) Historical fire regimes in red pine forests of
444 the Adirondack Mountains, New York, USA. *Natural Areas Journal* 39(2): 226–236.

445 Ali AA, Asselin H, Larouche AC et al. (2008) Changes in fire regime explain the Holocene rise
446 and fall of *Abies balsamea* in the coniferous forests of western Québec, Canada. *The Holocene*
447 18(5): 693–703.

448 Ali AA, Blarquez O, Girardin MP et al. (2012) Control of the multimillennial wildfire size in
449 boreal North America by spring climatic conditions. *Proceedings of the National Academy of
500 Sciences of the USA* 109(51): 20966–20970.

451 Ali AA, Carcaillet C and Bergeron Y (2009) Long-term fire frequency variability in the eastern
452 Canadian boreal forest: the influences of climate vs. local factors. *Global Change Biology*,
453 15(5): 1230–1241.

454 Asselin H, Payette S, Fortin M-J et al. (2003) The northern limit of *Pinus banksiana* Lamb. in
455 Canada: explaining the difference between the eastern and western distributions. *Journal of
456 Biogeography* 30(11): 1709–1718.

457 Bennett KD (1987) Holocene history of forest trees in southern Ontario. *Canadian Journal of
458 Botany* 65(9): 1792–1801.

459 Bergeron Y and Gagnon D (1987) Age structure of red pine (*Pinus resinosa* Ait.) at its northern
460 limit in Quebec. *Canadian Journal of Forest Research* 17(2): 129–137.

461 Bérubé Tellier A, Drevnick PE and Bertolo A (2016) Brook trout (*Salvelinus fontinalis*)
462 extinction in small boreal lakes revealed by ephippia pigmentation: a preliminary analysis.
463 *Advances in Oceanography and Limnology* 7(2): 197–205.

464 Blaauw M and Christen JA (2011) Flexible paleoclimate age-depth models using an
465 autoregressive gamma process. *Bayesian Analysis* 6(3): 457–474.

466 Blarquez O, Ali AA, Girardin MP et al. (2015) Regional paleofire regimes affected by non-uniform climate, vegetation and human drivers. *Scientific Reports* 5(1): 13356.

468 Blarquez O, Talbot J, Paillard J et al. (2018) Late Holocene influence of societies on the fire
469 regime in southern Québec temperate forests. *Quaternary Science Reviews* 180: 63–74.
470

Blarquez O, Vannière B, Marlon JR et al. (2014) paleofire: An R package to analyse sedimentary charcoal records from the Global Charcoal Database to reconstruct past biomass burning. *Computers & Geosciences* 72: 255-261.

471

472

473

Braadbaart F and Poole I (2008) Morphological, chemical and physical changes during charcoalification of wood and its relevance to archaeological contexts. *Journal of Archaeological Science* 35(9): 2434-2445.

474

475

476

Brisson J and Bouchard A (2003) In the past two centuries, human activities have caused major changes in the tree species composition of southern Québec, Canada. *Ecoscience*, 10(2): 236-246.

477

478

479

Brown M (2009) Low-intensity fire in eastern white pine. A supporting role in understory diversity. *Fire Science Brief* 52: 1-6.

480

481

Christianson, A. C., Sutherland, C. R., Moola, F., et al. (2022) Centering indigenous voices: The role of fire in the boreal forest of North America. *Current Forestry Reports* 8(3): 257-276.

482

483

Clifford J and Castonguay S (2022) British ghost acres and environmental changes in the Laurentian forest during the nineteenth century. *Journal of Historical Geography*, 78, 126-138.

484

485

Danneyrolles V, Arseneault D and Bergeron Y (2016) Pre-industrial landscape composition patterns and post-industrial changes at the temperate-boreal forest interface in western Quebec, Canada. *Journal of Vegetation Science* 27: 470-481.

486

487

488

Davis MB (2000) Palynology after Y2K – Understanding the source area of pollen in sediments. *Annual Review of Earth and Planetary Sciences* 28: 1-18.

489

490

Deevey ESJ (1965) Sampling lake sediments by use of the Livingstone sampler. In: Kummel (ed) *Handbook of paleontological techniques*. San Francisco: Freeman, pp.521-529.

491

492

Després, T., Asselin, H., Doyon, F. et al. (2017). Gap dynamics of late successional sugar maple-yellow birch forests at their northern range limit. *Journal of Vegetation Science* 28(2): 368-378.

493

494

495

Drever CR, Messier C, Bergeron Y et al. (2006) Fire and canopy species composition in the Great Lakes-St. Lawrence forest of Témiscamingue, Québec. *Forest Ecology and Management* 231(1-3): 27-37.

496

497

498

Engelmark O, Bergeron Y, Flannigan MD (2000) Age structure of eastern white pine, *Pinus strobus* L., at its northern distribution limit in Quebec. *Canadian Field-Naturalist* 114(4): 601-604.

499

500

501

Engstrom FB and Mann DH (1991) Fire ecology of red pine (*Pinus resinosa*) in northern Vermont, U.S.A. *Canadian Journal of Forest Research* 21(6): 882-889.

502

503

Environnement Canada (n.d.) *Normales climatiques du Québec 1981-2010*. Ministère de l'Environnement et de la Lutte contre les changements climatiques, de la Faune et des Parcs. https://www.environnement.gouv.qc.ca/climat/normales/sommaire.asp?cle=7018000

504

505

506

Gagnon S. (2024) *Impact de la sévérité du brûlage sur la régénération naturelle de pin blanc et de pin rouge*. Masters thesis, Université du Québec en Abitibi-Témiscamingue.

507

508

Glew JR (1991) Miniature gravity corer for recovering short sediment cores. *Journal of Paleolimnology* 5(3): 285-287.

509
Grenier JD, Bergeron Y, Kneeshaw D et al. (2005) Fire frequency for the transitional mixedwood forest of Timiskaming, Quebec, Canada. *Canadian Journal of Forest Research* 35: 656–666.

Hébert C, Domaine É and Bélanger L (2020) Prescribed burning to restore eastern white pine forests of La Mauricie National Park of Canada. In: Naqiyuddin Bakar A and Nazip Suratman M (eds) *Protected areas, national parks and sustainable future*. London: IntechOpen. https://www.intechopen.com/books/protected-areas-national-parks-and-sustainable-future/prescribed-burning-to-restore-eastern-white-pine-forests-of-la-mauricie-national-park-of-canada

Hennebelle A, Aleman JC, Ali AA, et al. (2020) The reconstruction of burned area and fire severity using charcoal from boreal lake sediments. *The Holocene*, 30(10): 1400–1409.

Hicks S and Hyvärinen H (1999) Pollen influx values measured in different sedimentary environments and their palaeoecological implications. *Grana* 38(4): 228–242.

Higuera P (2009) *CharAnalysis 0.9: Diagnostic and analytical tools for sediment-charcoal analysis*. https://github.com/phiguera/CharAnalysis

Jørgensen S (1967) A method of absolute pollen counting. *New Phytologist* 66(3): 489–493.

Larochelle É, Lavoie M, Grondin P et al. (2018) Vegetation and climate history of Quebec’s mixed boreal forest suggests greater abundance of temperate species during the early- and mid-Holocene. *Botany* 96(7): 437–448.

Liu K-B (1990) Holocene paleoecology of the boreal forest and Great Lakes-St. Lawrence Forest in Northern Ontario. *Ecological Monographs* 60(2): 179–212.

Lynch JA, Clark JS and Stocks BJ (2004) Charcoal production, dispersal, and deposition from the Fort Providence experimental fire: interpreting fire regimes from charcoal records in boreal forests. *Canadian Journal of Forest Research*, 34(8): 1642–1656.

Marchand N and Filion L (2014) A dendroecological analysis of eastern hemlock and white pine in relation to logging in La Mauricie National Park (Québec, Canada). *Forestry Chronicle* 90(03): 351–360.

Marschall JM, Stambaugh MC, Abadir ER, et al. (2022) Pre-Columbian red pine (Pinus resinosa Ait.) fire regimes of north-central Pennsylvania, USA. *Fire Ecology* 18: 11.

McRae DJ, Lynham TJ and Frech. R. J (1994) Understory prescribed burning in red pine and white pine. *Forestry Chronicle* 70(4): 395–401.

Montour S, Thériault M and Préfontaine V (2020) *Régénération du pin blanc et superficie brulée - Protocole et analyse des données*. Parc National de La Mauricie.

Mustaphi CJ, Davis EL, Perreault JT et al. (2015) Spatial variability of recent macroscopic charcoal deposition in a small montane lake and implications for reconstruction of watershed-scale fire regimes. *Journal of Paleolimnology* 54(1): 71–86.

Nyamai PA, Goebel PC, Hix DM et al. (2014) Fire history, fuels, and overstory effects on the regeneration-layer dynamics of mixed-pine forest ecosystems of eastern Upper Michigan, USA. *Forest Ecology and Management* 322: 37–47.
Oris F, Ali AA, Asselin H et al. (2014) Charcoal dispersion and deposition in boreal lakes from 3 years of monitoring: Differences between local and regional fires: Monitoring charcoal deposition in lakes. *Geophysical Research Letters* 41(19): 6743-6752.

Paillard J, Richard PJ, Blarquez O et al. (2023) Postglacial establishment and expansion of marginal populations of sugar maple in western Québec, Canada: Palynological detection and interactions with fire, climate and successional processes. *The Holocene* 33(10): 1237-1256.

Paquette N and Gajewski K (2013) Climatic change causes abrupt changes in forest composition, inferred from a high-resolution pollen record, southwestern Quebec, Canada. *Quaternary Science Reviews* 75: 169-180.

Pastor J (2023) *White pine: the natural and human history of a foundational American tree*. New York: Island Press.

Power MJ, Marlon J, Ortiz N, et al. (2008) Changes in fire regimes since the Last Glacial Maximum: an assessment based on a global synthesis and analysis of charcoal data. *Climate Dynamics* 30(7): 887-907.

Reimer PJ, Austin WEN, Bard E et al. (2020) The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP). *Radiocarbon* 62(4): 725-757.

Richard PJH (1993) *Origine et dynamique postglaciaire de la forêt mixte au Quebec*. *Review of Palaeobotany and Palynology* 79(1-2): 31-68.

Richard PJ, Fréchette B, Lavoie M, et al. (2025) Histoire postglaciaire de la végétation et du climat des domaines bioclimatiques des érablières à érable à sucre du Québec : un aperçu. *Naturaliste canadien* 149(2): 29-47.

Robles D, Bergeron Y, Meunier J et al. (2024) Climatic controls of fire activity in the red pine forests of eastern North America. *Agricultural and Forest Meteorology* 358: 110219.

Robles D, Boulanger Y, Pascual J et al. (2025) Timber harvesting was the most important factor driving changes in vegetation composition, as compared to climate and fire regime shifts, in the mixedwood temperate forests of Temiscamingue since AD 1830. *Landscape Ecology* 40: 26.

Saucier J-P, Gosselin J, Morneau C et al. (2010) Utilisation de la classification de la végétation dans l'aménagement forestier au Québec. *Revue forestière française* 62(3-4): 428-438.

Scherer SS, Kern CC, D'Amato AW, et al. (2018). Long-term pine regeneration, shrub layer dynamics, and understory community composition responses to repeated prescribed fire in *Pinus resinosa* forests. *Canadian Journal of Forest Research* 48(2): 117-129.

Schiks T, Bell FW, Searle EB et al. (2024) Prescribed fire promotes regeneration in a mature eastern white pine forest. *Forest Ecology and Management* 553: 121590.

Smirnova E, Bergeron Y and Brais S (2008) Influence of fire intensity on structure and composition of jack pine stands in the boreal forest of Quebec: Live trees, understory vegetation and dead wood dynamics. *Forest Ecology and Management* 255(7): 2916-2927.

Stambaugh MC, Abadir ER, Marschall JM, et al. (2021) Red pine (*Pinus resinosa* Ait.) fire history and management implications in the Mississippi River headwaters, Minnesota, USA. *Forest Ecology and Management* 494: 119313.
588 Terasmae J and Anderson TW (1970) Hypsithermal range extension of white pine (*Pinus strobus* L.) in Quebec, Canada. *Canadian Journal of Earth Sciences* 7(2): 406–413.
589

590 Tymstra C, Stocks BJ, Cai X and Flannigan MD (2020) Wildfire management in Canada: Review, challenges and opportunities. *Progress in Disaster Science*, 5: 100045.
591

592 Uprety Y, Asselin H, Bergeron Y et al. (2014) White pine (*Pinus strobus* L.) regeneration dynamics at the species’ northern limit of continuous distribution. *New Forests* 45(1): 131–147.
593

594 Weyenberg S, Frelich L and Reich P (2004) Logging versus fire: how does disturbance type influence the abundance of *Pinus strobus* regeneration? *Silva Fennica* 38(2): 179–194.
595

596
<table><caption>Table 1. Characteristics of the three sampled lakes.</caption><thead><tr><th></th><th>Pool</th><th>Couronne</th><th>à Sam</th></tr></thead><tbody><tr><td>Latitude (°N)</td><td>46°50'38"</td><td>46°46'32"</td><td>46°39'13"</td></tr><tr><td>Longitude (°W)</td><td>72°59'23"</td><td>72°50'03"</td><td>72°58'36"</td></tr><tr><td>Surface area (ha)</td><td>3.30</td><td>3.86</td><td>2.05</td></tr><tr><td>Elevation (m a.s.l.)</td><td>288</td><td>239</td><td>225</td></tr><tr><td>Maximum water depth (m)</td><td>5.00</td><td>10.90</td><td>6.25</td></tr><tr><td>Total length of sediments collected (cm)</td><td>419</td><td>436</td><td>260</td></tr><tr><td>Sedimentation rate (cm yr<sup>-1</sup>)</td><td>0.049</td><td>0.054</td><td>0.033</td></tr><tr><td>Date of last prescribed burn</td><td>2015</td><td>2007</td><td>2015</td></tr><tr><td>Distance to prescribed burn (m)</td><td>0</td><td>300</td><td>2000</td></tr></tbody></table>
600 **Figure captions**

Figure 1. a) Locations of the three sampled lakes in La Mauricie National Park (LMNP) as well as areas where prescribed burns were conducted since 1991, and where natural fires occurred between 1836 and 1970 (one natural fire occurred in 2003 and took longer than usual to extinguish, but only burned 385 ha, 8 km southeast of lake Pool). b) Locations of some of the previous studies having recorded high abundance of white pine and red pine during the Holocene Thermal Maximum in Quebec and Ontario (see Table S1).

Figure 2. Age-depth models for a) Lake Pool, b) Lake Couronne, and c) Lake à Sam, obtained from rbacon v.3.2.0 using the ¹⁴C dates listed in Table S2.

Figure 3. Charcoal accumulation rates recorded in the uppermost 10 cm of sediments from lake Pool (green) and lake Couronne (blue) (lake à Sam did not have charcoal within the top 10 cm). The horizontal dashed line corresponds to the surface fire signal, i.e., the maximum charcoal accumulation rate (0.058 mm²·cm⁻²·yr⁻¹) of the period when only surface fires (prescribed burns) occurred in the study area. Only the uppermost 7.5 cm were considered to identify the threshold, as from 8 cm and below, very high charcoal concentrations at lake Couronne are clearly indicative of crown fires having occurred before the fire suppression policy was introduced in the 1970s.

Figure 4. Figure 4. Holocene biomass burned based on charcoal accumulation rates at a) lake Pool, b) lake Couronne and c) lake à Sam. The horizontal red dashed line corresponds to the threshold value (0.058 mm²·cm⁻²·yr⁻¹) differentiating surface from crown fires. The red crosses represent high-severity crown fires, and the green crosses represent low-severity surface fires.

Figure 5. Holocene variations of the fire return interval (FRI) at the regional scale (a) and at lakes Pool (green), Couronne (blue) and à Sam (orange) (b). The shaded areas represent the 95% confidence intervals. The horizontal red dashed line represents the average regional FRI for the Holocene.

Figure 6. Regional biomass burned (mm²·cm⁻²·yr⁻¹) and regional fire return interval (years) from 9,600 cal. yr BP to the present, plotted alongside the abundance (percentage) of pollen grains of *Pinus banksiana*, *Pinus resinosa*, and *Pinus strobus*. Total pollen influx is also shown (grains·cm⁻²·yr⁻¹), as well as the ratio of key temperate to boreal taxa. Three pine pollen zones (PPZ) were identified from the CONISS analysis.