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New Macrofossil Evidence for Early Postglacial Migration of Jack Pine (Pinusbanksiana) in the James Bay Region of Northwestern QuebecAuthor(s): Claire Lacroix, Martin Lavoie & Najat BhirySource: Ecoscience, 18(3):273-278. 2011.Published By: Centre d'études nordiques, Université LavalDOI: http://dx.doi.org/10.2980/18-3-3450URL: http://www.bioone.org/doi/full/10.2980/18-3-3450

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18 (3): 273-278 (2011)

The distribution of jack pine (Pinus banksiana) extends farther into northern Quebec than that of any other pine. It is the second most common tree species in the lichen woodland bioclimatic domain, after black spruce (Picea mariana). In the James Bay region, in northwestern Quebec, the northern limit of jack pine today is located in the valley of the Great Whale River, where it colonizes river terraces (Desponts & Payette, 1992; Figure 1). Generally, its distribution is associated with sandy, well-drained, and nutrient-poor habitats (Payette, 1993). It is a fire-prone species that can form pure stands, particularly on terraces that line major rivers (Sirois, 1996). In the James Bay region, the fire cycle is estimated at approximately 100–120 y (Payette et al., 1989; Parisien & Sirois, 2003), but shorter fire intervals, on the order of 60 to 80 y, have been observed for terraces colonized by jack pine (Desponts & Payette, 1992). According to Asselin et al. (2003), low fire frequency and small f ire size are among the main factors that prevented jack pine from migrating further north following deglaciation in northern Quebec.

Our knowledge of the postglacial migration of jack pine to northwestern Quebec rests in large part on pollen

diagrams obtained from the analysis of lake and peat sediments and used to reconstruct the regional vegetation history (Richard, 1979; Gajewski, Payette & Ritchie, 1993; Gajewski, Garralla & Milot-Roy, 1996; Ferland, 2007; Beaulieu-Audy et al., 2009; Magnan, 2009). Available pollen data (Figures 1 and 2) suggests that the generalized spread of jack pine in the southern part of the region would have begun about 4500–4000 cal y ago, a period during which pollen percentages for the species show a significant increase (Figure 2, for example, sites Droséras, Bereziuk, CHISM-II). However, the high percentages recorded at the bottom of pollen diagrams are the result of long distance pollen transport from jack pine populations located further to the south. The species would have attained its northern limit of distribution around 3200 cal BP, as demonstrated by the macroremains (cone scales, needles) found in dune paleosols (Desponts & Payette, 1993). This matches an increase in the pollen representation of the species recorded at more northerly sites (CHISM-I, GB1, and PLE sites) (Richard, 1979; Gajewski, Garralla & Milot-Roy, 1996; Laframboise, 2011). It was not until around 2300 cal BP, however, that jack pine would have been commonly present at its northern limit (Desponts & Payette, 1993).

It is difficult to establish precisely the period when jack pine arrived in the James Bay region due to long distance pollen transport and the fact that pine is a relatively high pollen producer. Modern pollen analogues suggest that

New macrofossil evidence for early postglacial migration of jack pine (Pinus banksiana) in the James Bay region of northwestern Quebec1

Claire LACROIX, Martin LAVOIE2 & Najat BHIRY, Département de géographie and Centre d’études nordiques, Université Laval,

Québec, Québec G1V 0A6, Canada, martin.lavoie@cen.ulaval.ca

Abstract: In the James Bay region of northwestern Quebec, earlier pollen data suggests that regional expansion of jack pine occurred around 4500–4000 cal BP, a period for which the species’ pollen curve shows a marked increase in pollen diagrams. New macrofossil data from charred dune paleosols in the Radisson area indicates that the species has been present in this region since at least 6300 cal BP, despite a representation of only about 1% in pollen assemblages. The postglacial migration of jack pine is an example of low-density migration. The first individuals were probably restricted to dry sites such as eoliandeposits and river terraces, upon which more frequent fires had a greater impact.Keywords: James Bay, paleosol, palynology, Pinus banksiana, plant-macrofossil, postglacial migration.

Résumé : Dans la région de la baie de James au nord-ouest du Québec, les données polliniques suggèrent que l’expansion régionale du pin gris aurait eu lieu vers 4500–4000 étal. BP, à l’époque où la courbe pollinique de l’espèce dans les diagrammes polliniques montre une augmentation marquée. De nouvelles données macrofossiles provenant de paléosols dunaires carbonisés dans la région de Radisson indiquent que l’espèce est présente dans cette région depuis au moins 6300 étal. BP, malgré une représentation d’à peine 1 % dans les assemblages polliniques. La migration postglaciaire du pin gris est un exemple d’une migration à faible densité. Les premiers individus étaient sans doute restreints aux stations les plussèches comme les dépôts éoliens et les terrasses fluviatiles affectées par le passage plus fréquent des feux.Mots-clés : Baie de James, macrorestes végétaux, migration postglaciaire, paléosols, palynologie, Pinus banksiana.

Nomenclature: Marie-Victorin, 1995.

Introduction

1Rec. 2011-03-14; acc. 2011-06-21.Associate Editor: Warwick F. Vincent.

2Author for correspondence.DOI 10.2980/18-3-3450

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a representation of 8% corresponds to its northern limit in eastern Canada, where this species is present in small stands (King, 1993), whereas the pollen spectra of surface samples from lakes in the James Bay region (Richard, 1979) show values for jack pine varying from 3.1 to 27.2% (average: 15.5%). Davis and Jacobson (1985) use 10% jack pine pollen to establish the presence of this taxon in New England during the Holocene. However, it is possible that some individuals may have migrated to the James Bay region prior to the generalized expansion of the species as defined by the marked increase of jack pine percentages, hence before a pollen threshold of 8–10% was reached in the pollen diagrams.

The exact timing for the migration of Pinus banksianainto the James Bay region is unresolved with existing pollen data. Therefore, we propose to use macrofossil data to document the presence of this tree. Macrofossils are important in the study of vegetation history because they indicate the local occurrence of taxa (Birks, 2007). Using

macroremains, we can specify and re-evaluate the epoch when a species migrated to a particular region (Jackson et al., 1997). The macrofossil data we present here is from charred organic layers in dune paleosols of the Radisson region (Figure 1) and shows that the postglacial migration of jack pine into the James Bay region occurred rather early, i.e., 6300 cal y ago.

Methods

An eolian deposit located near the La Grande Rivière Airport (53° 37' N, 77° 41' W) was excavated to search for paleosols and charred organic matter. This eolian deposit was also studied as part of a larger study on the Holocene chronology of forest fires and eolian processes in the Radisson area (Lacroix, 2011) and was selected for this paper because it contains the oldest paleosols we found in the region. Consisting of an elongated dune in a north–south orientation at an altitude of 205 m,

100 km

56° N

54° N

52° N

Hudson Bay

James Bay

80° W

FOREST TUNDRA

BOREALFOREST

Whapmagoostui-Kuujjuarapik

CHISM-II

Bereziuk

PLE

GB1

Great Whale River

LG3

56° N

54° N

0

Radisson

LICHEN WOODLAND

CHISM-I

2

Quebec

60° N

80° W 60° W

50° N

70° W

1 2

FIGURE 1. Map of northwestern subarctic Québec showing the bioclimatic domains, the study site (star; Airport and Droséras), the northern limit of Pinus banksiana (broken line), and other sites mentioned in the text: 1: Pessière (Carcaillet et al., 2001); 2: CH2 (Garralla & Gajewski, 1992); CHISM-I, CHISM-II, and Bereziuk (Richard, 1979); LG3 (Paître, 2008); GB1 (Gajewski, Garralla & Milot-Roy, 1996); PLE (Laframboise, 2011). Information about these sites is shown in Table I.

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the sides are steeply inclined, upstream to the west and downstream to the east. The summit of the dune is at a height of about 20 m, and the crest is about 15 m wide. The deposit is mainly colonized by Pinus banksiana, Vaccinium angustifolium, and Cladonia stellaris.

Five sections, labelled AN1 to AN5, were excavated on the eastern slope of the dune. All paleosols were described using the Canadian system of soil classification (Soil Classif ication Working Group, 1998) and were subjected to stratigraphic, chemical, and granulometric analyses (Lacroix, 2011). One 50-cm3 was retrieved from each layer of charred organic material in the paleosols for plant-macrofossil analysis to reconstruct the local vegetation cover present on the dune at each period of f ire incidence. AMS radiocarbon dating of charcoal particles was conducted for all charred organic layers in the Université Laval’s Radiocarbon Dating Laboratory (ULA) and at the Keck Laboratory of the University of California (UCIAMS). Only 1 layer (AN4-3) was dated

using the conventional 14C method (charcoal particles). Radiocarbon ages (14C BP) were calibrated (cal BP) using the CALIB 6.0.1 program (Stuiver & Reimer, 1993) and the INTCAL09 data set (Reimer et al., 2009). Calibrated dates were rounded to the nearest 10 y using 2σ cal age ranges. In order to reconstruct the postglacial history of the regional vegetation, pollen and spore analyses were also conducted on a sediment core 170 cm thick removed from the edge of a lake (Lac aux Droséras, unofficial name) located about 8 km south of the eolian deposit. For comparison purposes, pollen curves for jack pine (expressed in percentages) for other sites in the James Bay area and northern boreal forest are also presented (Figures 1 and 2; Table I). The data are from the North American Pollen Database with the exception of data from Lac à la Pessière (provided by Laboratoire Jacques-Rousseau, Université de Montréal). The jack pine pollen curves (Figure 2) are presented as a function of time (calibrated years), based on an age–depth model using linear interpolation.

Pessière0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10 000

Age

(ca

l BP

)

0 5 10 15 20 25

CHISM-IDroséras Bereziuk PLECHISM-II

Percentages

GB1CH2

0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 0 5 10 15 20 0 5 10 15 20 25 0 5 0 5 10

FIGURE 2. Pollen data (percentages) of Pinus banksiana according to time (cal BP) for selected sites in the James Bay region. The sites are presented as a function of a south–north gradient. The 40 uppermost centimetres of the core (< 1200 cal y) from Lac aux Droséras were not analyzed because of the fibrous nature of the sediments and the very low associated pollen content.

TABLE I. Sites in the James Bay area and northern boreal forest mentioned in the text (Figure 1).

Site Latitude Longitude Paleoecological data* Reference

Pessière (lake) 49° 30' N 79° 14' W M-P Carcaillet et al., 2001CH2 (lake) 49° 41' N 74° 35' W M-P Garralla & Gajewski, 1992CHISM II (lake) 53° 05' N 76° 20' W P Richard, 1979LG3 (peat bog) 53° 25' N 73° 52' W M Paître, 2008Droséras (lake) 53° 32' N 77° 39' w P This study; Lacroix, 2011Aéroport (eolian deposit) 53° 37' N 77° 41' W M This study; Lacroix, 2011Bereziuk (lake) 54° 02' N 76° 07' W P Richard, 1979CHISM I (lake) 54° 47' N 76° 08' W P Richard, 1979GB1 (lake) 55° 07' N 75° 15' W P Gajewski, Garralla & Milot-Roy, 1996PLE (lake) 55° 20' N 77° 37' W M-P Laframboise, 2011

*M: macrofossil; P: pollen

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Results

Stratigraphic analysis and pedological profiles of soil sections allowed identification of 1 to 4 paleosols in each section of the dune (Table II). AMS radiocarbon dating determined ages varying between 6360 and 6380 cal BP for the oldest paleosols (AN1-3, AN5-2) and 80 cal BP for the most recent (AN4-3). All buried soils were characterized by the presence of abundant charred organic matter and numerous macroscopic charcoal fragments.

In total, macroscopic charred remains of 13 plant taxa were identif ied among the macrofossil assemblages of the samples analyzed (Table II): 3 tree taxa belonging to the Pinaceae family (Larix laricina, Picea sp., and Pinus banksiana; remains of scales, leaves, and seeds), 5 shrub taxa of the Ericaceae family (Arctostaphylos alpina;A. Uva-Ursi, Vaccinium sp., V. angustifolium, and V. vitis-idaea; remains of leaves and seeds), 1 shrub taxon of the Empetraceae family (Empetrum nigrum; remains of seeds and leaves), and 4 plant taxa belonging to the Cyperaceae (Carex sp.; seed remains), Cornaceae (Cornus canadensisand C. suecica; seed remains), and Papaveraceae families (Corydalis sempervirens; seed remains). Sclerotia of the mycchorizal fungus Cenococcum graniforme were also found in all samples. For the samples as a whole, remains of Picea sp. and Pinus banksiana were most abundant. Remains of jack pine and spruce (especially needles) were present simultaneously in all paleosols, reflecting the local establishment of a mixed community, including the oldest, dating from 6360 to 6380 cal BP (AN1-3 and AN5-2;10 and 4 macroremains·50 cm–3 of Pinus banksiana) and 4920 cal BP (AN3-4; 20 macroremains·50 cm–3 of Pinus banksiana). Only sample AN5-9 (2900 cal BP) did not contain any spruce macroremains (Table II). Despite the limited diversity of taxa found in the plant-macrofossil assemblages, these results are similar to those for macrofossil assemblages from other dune paleosols in the

northern part of the lichen woodland in northern Quebec (Filion, 1984; Desponts, 1990).

Discussion

Macrofossil analyses of the eolian deposit from the airport sector indicate that jack pine was present in the region as far back as 6300 cal BP. In the eolian deposit of that period, it was part of a mixed community, accompanied by spruce (most probably black spruce). Jack pine must have been relatively scarce, however, both locally and regionally. In fact, the quantities of macroremains found in the layers of organic material dating from 6380 (AN5-2) and 6360 cal BP (AN1-3) are quite low compared to other, more recent buried layers of organic material from the same deposit (Table II). The pollen representation of jack pine is very low during this period in the pollen diagrams for the area closest to the deposit studied, despite the fact that this tree is a high pollen producer. In the pollen diagram of Lac aux Droséras, the percentages of the species are below 1% (Figure 2). However, they are slightly higher (3–5%) for a peat bog complex located just north of La Grande Rivière Airport (LG2 peatland, Beaulieu-Audy et al., 2009), likely because of its proximity to the eolian deposit (5 km) and the vastly greater surface area of the peatland, which would probably have enabled it to register more significant regional pollen influx. In the eolian deposits of the Rivière Nécopastic sector, the oldest macroremains of jack pine were dated to 3960 cal BP, which corresponds to the second oldest charred paleosol found at this location. No jack pine macroremains were found in the oldest paleosol, dated to 5420 cal BP (Lacroix, 2011).

Recently, other studies have also demonstrated the presence of jack pine locally prior to the marked increase in percentages in the pollen diagrams. Megafossils and macroremains of the species were found preserved in a minerotrophic peatland in proximity to the eolian deposit

TABLE II. Macrofossil data (number of macroremains per 50 cm3 of sediment).

Organic layers AN1-11 AN1-8 AN1-7 AN1-3 AN2-5 AN2-3 AN3-4 AN4-3 AN5-9 AN5-7 AN5-5 AN5-2

Conventional age (14C BP) 365 ± 20 1385 ± 15 1355 ± 20 5595 ± 25 115 ± 20 3060 ± 15 4380 ± 20 30 ± 60 2790 ± 20 2770 ± 20 3360 ± 15 5550 ± 25

Calibrated age (cal BP) 460 1300 1290 6360 100 3290 4920 80 2900 2860 3390 6380

Laboratory number ULA 1157 1377 1156 1148 1390 1378 1379 3300 1155 1159 1575 1147

Laboratorynumber UCIAMS 65014 69885 65013 65005 70717 69886 69887 - 65012 65016 75752 65004

Picea sp. 66 6 5 1 1081 338 52 504 0 392 169 79Pinus banksiana 165 43 14 10 2133 436 20 1429 43 134 143 4Larix laricina 0 1 0 0 1 0 1 1 0 0 0 24Arctostaphylos uva-ursi 0 0 0 0 2 1 0 0 1 0 3 2Arctostaphylos alpina 0 0 0 0 1 0 0 0 1 0 0 2Empetrum nigrum 1 0 0 0 0 0 0 0 0 1 0 0Vaccinium sp. 0 0 0 0 1 0 0 2 0 0 0 0Vacinium angustifolium 1 1 4 0 1 2 0 3 0 0 2 0Vaccinium vitis-idaea 0 0 0 0 2 0 1 1 0 0 0 0Carex sp. 0 0 0 0 0 1 0 0 0 0 1 0Corydalis sempervirens 0 0 0 0 0 0 0 1 0 0 0 0Cornus canadensis 0 0 0 0 0 0 0 0 1 0 0 0Cornus suecica 0 0 0 0 0 0 0 0 0 0 0 1Cenococcum graniforme 109 119 281 0 87 69 30 1166 32 7 112 22

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we studied, and were dated to 4950 cal BP (Arseneault & Sirois, 2004). Approximately 300 km to the east, in the LG3 sector (Figure 1), jack pine macroremains dating from 5450 cal BP were found at the base of a peat bog that today forms an enclave within a jack pine forest (Paître, 2008).

The discovery of jack pine macroremains dating from 6300 cal BP implies that the species arrived in the James Bay region earlier and probably also migrated more quickly than pollen data alone would suggest, because the species was likely present farther south during the afforestation stage at the Pessière site (Figures 1 and 2), which started 7650 cal BP (Carcaillet et al., 2001), and in the Chibougamau area (Lake CH2; Figure 1), which started around 8400 cal BP (Garralla & Gajewski, 1992; Payette, 1993). The pollen diagram of the CHISM-II site (Figure 1) shows that the vegetation cover of this period was an open spruce forest where green alder (Alnus crispa) played an important role and paper birch (Betula papyrifera) was present (Richard, 1979). In the Radisson area, pollen spectra at the base of the diagram of Lac aux Droséras show the presence of tree species such as trembling aspen (Populus tremuloides), eastern larch (Larix laricina), and spruce (Picea sp.) prior to 7100 cal BP. Subsequently, a marked increase of the percentages of Picea sp. and total pollen concentrations (grains·cm–3) suggest that a spruce–green alder forest formed. Jack pine was therefore present in the Radisson area 700 y after the formation of its first spruce forests, arriving at the period corresponding to the onset of an increase in the July mean temperature estimated from fossil pollen records using the modern analog technique (Viau & Gajewski, 2009). An increase in microcharcoal in the sediments of a lake located in the airport sector (Ferland, 2007) occurs at this same period, reflecting the incidence of regional forest fires.

Prior to the clear increase in jack pine percentages depicted in the diagram of Lac aux Droséras, reflecting the onset of the regional expansion of jack pine around 4500 cal BP, the average pollen representation of the species was very low, 0.8% between 7100 and 4500 cal BP, despite its presence in the region (Figure 2). Our results prove that Pinus banksiana was indeed present, although at percentages less than 1%, a level at which it is very difficult to detect small, isolated populations using pollen analysis (Peteet, 1991; Willis, Rudner & Sümegi, 2000). The average pollen representation of the species then rose to 8% between 4500 and 1200 cal BP at Lac aux Droséras, reaching a maximum of 15%. Following its migration into the Radisson area, a period of about 3000 y was required for the species to attain its northern limit of distribution, around 3200 cal BP at Great Whale River (Desponts & Payette, 1993).

Conclusion

The results of our study support the thesis proposed by Desponts and Payette (1993), according to which the postglacial migration of jack pine to northwestern Quebec was characterized by low density and the species survived at this low density before experiencing the regional expansion reflected in the increase of its pollen representation. During this low-density migration, the species was very likely

restricted to the driest, sandiest sites, such as scattered dunes or river terraces, which would have been more susceptible to fire incidents. The use of a pollen percentage threshold (8–10% in the case of jack pine) would probably be more appropriate in cases of massive migration (like an advancing front), whereas for species migrating via outposts, thresholds are less efficient in revealing species’ arrival. The subsequent expansion of jack pine throughout the region over the course of recent millennia was no doubt associated with an increased frequency of forest f ires. For some other forests, such as the boreal forest south of Hudson Bay, data based on continuous analysis of macroscopic charcoal preserved in lake sediment illustrates aspects of the Holocene fire regime (Hély et al., 2010). While no such data are available to date for the Radisson area, jack pine’s expansion corresponds with an increase in microscopic charcoal concentrations in sediments (Richard, 1979; Ferland, 2007).

Acknowledgements

We would like to thank É. Lessard and É. C. Robert for f ield and laboratory assistance. Thoughtful comments from W. F. Vincent (Guest Editor) and three anonymous reviewers were greatly appreciated. This research received financial support through grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to M. Lavoie and N. Bhiry and through a grant from Indian and Northern Affairs Canada (Northern Scientific Training Program) to C. Lacroix.

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