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Postglacial Vegetation at the Northern Limit of Lichen Woodland In Document generated on 09/30/2021 12:39 a.m. Géographie physique et Quaternaire Postglacial Vegetation at the Northern Limit of Lichen Woodland in Northwestern Québec La végétation postglaciaire à la limite septentrionale de la pessière à lichens du nord-ouest du Québec Postglaziale Vegetation an der nördlichen Grenze des Flechten-Tannenwalds in Nordwest-Québec Konrad Gajewski, Silvina Garralla and Valérie Milot-Roy Spécial Québec Article abstract Volume 50, Number 3, 1996 Three pollen diagrams from the northern part of the lichen woodland in northwestern Québec show broadly similar Holocene vegetation sequences. URI: https://id.erudit.org/iderudit/033104ar Following deglaciation, shortly after 6000 yr BP, shrub and herbaceous tundra DOI: https://doi.org/10.7202/033104ar plants dominated briefly; Larix Iaricina, Populus and Juniperus were also important elements of the landscape. A maximum of AInus crispa and Betula See table of contents was followed by a period dominated by Picea. In the northernmost site, the forests opened in response to neoglacial cooling during the past 1000 years. Today only black spruce (Picea mariana) grows in northwestern Québec and there is no evidence that white spruce (P. glauca) ever migrated into the region. Publisher(s) Les Presses de l'Université de Montréal ISSN 0705-7199 (print) 1492-143X (digital) Explore this journal Cite this article Gajewski, K., Garralla, S. & Milot-Roy, V. (1996). Postglacial Vegetation at the Northern Limit of Lichen Woodland in Northwestern Québec / La végétation postglaciaire à la limite septentrionale de la pessière à lichens du nord-ouest du Québec. Géographie physique et Quaternaire, 50(3), 341–350. https://doi.org/10.7202/033104ar Tous droits réservés © Les Presses de l'Université de Montréal, 1996 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ Géographie physique et Quaternaire, 1996, vol. 50, n° 3, p. 341-350, 7 fig., 3 tabl., 1 ann. POSTGLACIAL VEGETATION AT THE NORTHERN LIMIT OF LICHEN WOODLAND IN NORTHWESTERN QUÉBEC Konrad GAJEWSKI*, Silvina GARRALLA", and Valérie MILOT-ROY; first author: Department of Geography, University of Ottawa, 165 Waller Street, Ottawa, Ontario K1N 6N5; second and third authors: Centre d'études nordiques, Université Laval, Sainte-Foy, Québec G1K 7P4. ABSTRACT Three pollen diagrams from RÉSUMÉ La végétation postglaciaire à la ZUSAMMENFASSUNG Postglaziale Vegeta­ the northern part of the lichen woodland in limite septentrionale de la pessiere à lichens tion an der nôrdlichen Grenze des Flechten- northwestern Québec show broadly similar du nord-ouest du Québec. Trois diagrammes Tannenwalds in Nordwest-Québec. Drei Pol­ Holocene vegetation sequences. Following polliniques provenant de la limite septentrio­ len-Diagramme vom nôrdlichen Teil des déglaciation, shortly after 6000 yr BP, shrub nale de la pessiere à lichens du nord-ouest Flechten-Tannenwalds in Nordwest-Québec and herbaceous tundra plants dominated du Québec montrent des séquences en zeigen in groBen Zùgen àhnliche Vegetations- briefly; Larix Iaricina, Populus and Juniperus grande partie similaires durant l'Holocène. Sequenzen wâhrend des Holozan. Nach der were also important elements of the land­ Après la déglaciation, survenue vers 6000 BP, Enteisung, kurz nach 6000 Jahren v.u.Z., scape. A maximum of AInus crispa and la végétation de la région a été dominée par dominierten eine kurze Zeit lang Pfianzen der Betula was followed by a period dominated les plantes herbacées et arbustives de la Busch- und Gras-Tundra; Larix laricina, by Picea. In the northernmost site, the for­ toundra. Larix laricina, Populus et Juniperus Populus und Juniperus waren auch wichtige ests opened in response to neoglacial cool­ ont aussi constitué des éléments importants Elemente der Landschaft. Auf ein Maximum ing during the past 1000 years. Today only du paysage. Un maximum 6'AInus crispa et von AInus crispa und Betula folgte eine von black spruce (Picea mariana) grows in north­ de Betula a été suivi par une période domi­ Picea beherrschte Période. Im nôrdlichsten western Québec and there is no evidence née par Picea. Dans le site le plus nordique, Teil Ôffneten sich die Wâlder wàhrend der that white spruce (P. glauca) ever migrated les forêts se sont ouvertes durant les 1000 letzten 1000 Jahre als Reaktion auf eine into the region. dernières années en réponse au refroidisse­ neoglaziale Abkûhlung. Heute wâchst nur die ment néoglaciaire. Actuellement, seule l'épi- schwarze Fichte (Picea mariana) in Nordwest- nette noire (Picea mariana) croît au nord- Québec und es gibt keinen Beleg dafùr, daR ouest du Québec, et les résultats laissent die WeiRtanne (Picea glauca) jemals in die croire que l'épinette blanche (P. glauca) ne Region wanderte. s'est jamais établie dans la région. Manuscrit reçu le 11 octobre 1995 ; manuscrit révisé accepté le 30 avril 1996 * e-mail address: [email protected] ** present address: PRINGEPA, CONICET, Casilla de Correo 128, 3400 Corrientes, Argentina 342 K. GAJEWSKI, S. GARRALLA and V. MILOT-ROY INTRODUCTION A late Holocene cooling (Neoglaciation) is interpreted from proxy-climate data from a number of sites in the northern part Studies of past positions of arctic treeline of North America of North America. Richard (1981), Lamb (1985) and Gajewski have indicated that significant displacements occurred in et ai (1993) have identified an opening of the forest-tundra western Canada during the Holocene. These changes include in response to this cooling in eastern North America. The data a northward advance of Picea in the MacKenzie Delta region presented here will further detail how this cooling influenced in the early Holocene (10 000 yr BP), followed by a retreat the vegetation at the transition from lichen woodland to forest- after 7000 yr BP (Spear, 1983, 1993; Ritchie, 1984). A simi­ tundra. lar sequence has been found in central Canada, but it oc­ curred later, with an advance and subsequent retreat between METHODS 5500 and 3500 yr BP (Nichols, 1975; Moser and MacDonald, 1990). In eastern Canada, Picea arrived at its present-day Sediment cores were collected with a Livingstone square- limit shortly after déglaciation less than 6000 yr BP. Treeline rod piston sampler from a raft which was anchored at three has not since retreated southward, although pollen records points in the lake. The uppermost sediment was collected with indicate opening of the forest-tundra during the past 2000 a clear plastic tube which had been fitted with a piston. The years (Richard, 1981; Gajewski et ai, 1993). Lamb (1985) tube was kept vertical until sediments were extruded in the found a decrease in the altitude of treeline in the past 3000 laboratory at the field station. years in Labrador. Weight-loss-on-ignition was estimated by drying one-mL Climatic changes can be inferred from these variations, subsamples overnight at 1000C and then igniting them for as the location of treeline is associated with the mean posi­ three hours at 550 0C. Bulk sediment samples were submit­ tion of the arctic front in July (Bryson, 1966). However, esti­ ted for radiocarbon dating after carefully cleaning the core mating past climates from the reconstruction of treeline move­ surface.One-mL subsamples of the sediment were processed ment has proven difficult. Due to difficulties of access, few for pollen analysis using standard methods as described in paleoecological sites have been analyzed and there are large Gajewski et ai (1993). This includes treatment of the sedi­ intervening areas with no treeline data. At most sites, sedi­ ment with 10% HCI, 10% KOH, HF and acetolysis solution, mentation rates are low and the sediments are relatively in­ and mounting the residue in silicon oil. The pollen sum varies organic, limiting the temporal resolution and precision of the between 480 and 955 grains per spectrum. Species discrimi­ pollen record. Consequently, only broad-scale inferences can nation of Picea pollen is discussed in Appendix 1. be made when correlating vegetation changes between sites. Our work provides additional sites in northwestern Québec STUDY AREA to improve the spatial resolution of the regional vegetation reconstructions. In northwestern Québec, the present-day transition from open forest to tundra occurs over two degrees of latitude In a previous study (Gajewski et ai, 1993) we presented through a broad forest-tundra, which is a mosaic of tundra four pollen diagrams from the region, one from each of the and forest communities (Payette, 1983). This forest-tundra is vegetation zones making up the forest - tundra transition (li­ further subdivided into a northern shrub and a southern ar­ chen woodland, forest-tundra forest subzone, forest-tundra boreal subzone (Fig. 1), depending on the predominant form shrub subzone, shrub-tundra). The broad-scale similarities of of the spruce trees present. The density of trees on the land­ the three diagrams from the lichen woodland and forest-tundra scape decreases irregularly from south to north (Payette, were noted. A fourth pollen diagram from the tundra showed 1983). no changes during the past 6000 years, and further studies confirmed that Picea had never been north of its present day Lake GB1 (informal name) is located on top of a hill just to limit in the past 6000 years (Gajewski and Garralla, 1992). the south of the valley of the Grande Rivière de la Baleine. One of the questions to be addressed here is: how repre­ The regional forests are an open lichen woodland dominated sentative is one pollen diagram of the vegetation history of by black spruce {Picea mariana); larch (Larix laricina) is also its vegetation zone? Does the low density of available pollen present although less abundant.
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