A 2233-year tree-ring chronology of subarctic black spruce (Picea mariana): growth forms response to long-term climate change

Abstract

We present the longest tree-ring chronology to date in northeastern North America (2233 years; 227 BCE -2005 CE), resulting from several research projects conducted at the subarctic treeline in northern Quebec. This raw chronology of tree-ring width includes 464 black spruce (Picea mariana (Mill.) B.S.P.) shrubs (krummholz) growing in wetlands and preserved within peatlands. An indexed series of 152 erect black spruce trees that have lived in wetlands is also presented, covering the period 216 BCE to 1619 CE. We compared these chronologies to a tree-ring series including 116 black spruce trees and krummholz having grown on well-drained lichen woodlands over the period 1304-2000 CE. These chronologies highlight the major climatic periods of the last two millennia. Floating chronologies dating from 2500 to 3500 years ago were also developed from trees preserved in frozen peat. Growth rings from this period are much wider than those of the last 2233 years, suggesting warm climatic conditions and permafrost-free peatlands during the transition from mid-to late Holocene. The three subarctic chronologies presented here underscore the relevance and usefulness of tree growth rings and growth forms as ecological tools to assess the influence of climate on subarctic ecosystems. RÉSUMÉNous présentons une synthèse des recherches menées à la limite des arbres du Québec subarctique qui ont permis la confection d'une série dendrochronologique couvrant 2233 ans, entre l'an 227 AEC (AEC 'avant l'ère courante', soit avant l'an 0 de notre ère) et l'an 2005 EC (EC 'ère courante', soit après l'an 0 de notre ère). Il s'agit de la plus longue série produite à ce jour dans le nord-est de l'Amérique du Nord. Cette série de largeur de cernes a été confectionnée à partir de 464 épinettes noires (Picea mariana (Mill.) B.S.P.) arbustives (krummholz) établies dans des milieux humides et préservées dans des tourbières. Une série indicée de 152 épinettes noires arborescentes ayant vécu dans des milieux humides est également présentée. Elle couvre la période 216 AEC à 1619 EC. Ces séries sont comparées à une série confectionnée à partir de 116 épinettes noires (arbres et arbustes) de sols bien drainés de pessières à lichens couvrant la période 1304-2000 EC. Les séries dendrochronologiques mettent en relief les grandes périodes climatiques des deux derniers millénaires. Des chronologies flottantes datées entre 2500 et 3500 ans avant aujourd'hui ont été construites à partir d'arbres ayant poussé dans des tourbières maintenant sous l'influence du pergélisol. Les cernes de croissance des arbres de cette période sont beaucoup plus larges que ceux des 2233 dernières années, suggérant l'influence d'un climat plus chaud qu'aujourd'hui, au passage de l'Holocène moyen à l'Holocène supérieur. Les chronologies subarctiques présentées dans ce travail soulignent la pertinence et l'utilité des formes de croissance et des cernes de croissance des arbres comme outils écologiques pour évaluer l'influence du climat sur les écosystèmes subarctiques.

Pollen in Polar Ice Implies Eastern Canadian Forest Dynamics Diverged From Climate After European Settlement

“…The ACT11d site is highly sensitive during the pine flowering season to this area (values of 200–1,000 μg m −2 yr −1 /(kg s −1 )) based on FLEXPART simulations (Figure 1). There is no evidence that the northern tree line in eastern Canada, mainly composed of spruce, has shifted geographically over the past millennium, so compositional changes in boreal forests (i.e., density of pine trees and pine pollen productivity, Viau & Gajewski, 2009), as well as southwards expansion into temperate regions (Lafontaine‐Boyer & Gajewski, 2014; Sanger et al., 2021), may have driven the observed increases in pine pollen rather than northward expansion of boreal forests (Delwaide et al., 2021). In addition, the colder conditions at the beginning of the LIA (Carcaillet & Richard, 2000) may have favored pine expansions in drying wetland areas in eastern Canada that subsequently provided suitable growth conditions in formerly wet soils for the fast‐spreading pioneer species.…”

“…The conifer pollen increase after 1400 CE (Figure S6 in Supporting Information ) is consistent with several local lake sediment‐based reconstructions (from e.g., Lac Brulé, Lac Noir, and Clear Pond) interpreted as local vegetation responses to the onset of the LIA in the North American boreal forest biome (Gajewski, 1988; Viau & Gajewski, 2009; Williams et al., 2018). Although some records along the northern margin of boreal forests indicate unfavorable conditions for conifers (Delwaide et al., 2021) in response to cooling conditions during the LIA, vegetation change recorded in ACT11d indicates an increase of pine pollen, possibly derived from vast Pinus banksiana stands in the eastern Canadian boreal forest belt or white pine ( Pinus strobus ) further south in mixed conifer forests (Flora of North America, 1993). For example, pine expanded relative to other conifer taxa around 1400 CE at Lac Brulé, Lac Noir, and Tawny Pond; lakes in southern Québec and Ontario that are today located in the mixed conifer belt south of the boreal forest (Figure S5 and S6 in Supporting Information ) (Lafontaine‐Boyer & Gajewski, 2014; Williams et al., 2018).…”

Millennial-Scale Solar Variability in Tree Rings of Northern Fennoscandia at the End of the Holocene

“…Millennial growth tree-ring chronologies are useful to reconstruct long-term climatic variations. To date, some tree-ring chronologies based on living and dead (subfossil) trees are currently available for the last several millennia (Naurzbaev and Vaganov 2000;Grudd et al 2002;Buckley et al 2004;Cook, 2006;Helama et al 2008;Arseneault et al 2013;Salzer et al 2019;Stahle et al 2019;Büntgen et al 2020;Pearl et al 2020;Delwaide et al 2021).…”