Reconstructed high-resolution forest dynamics and human impacts of the past 2300 years of theParc national de Mont-Orford, southeastern Québec, Canada

Abstract

We used a high-resolution lacustrine pollen record from Étang Fer-de-Lance (45°21′21.9′N, 72°13′35.3′W), southeastern Québec, Canada, together with microcharcoal, to infer forest dynamics and human impacts over the past 2300 years. The lake is located in the eastern sugar maple-basswood forest domain of the Northern Temperate Forest of eastern North America. We found that the pollen percentages and influxes of Fagus grandifolia (American beech) and Tsuga canadensis (eastern hemlock) significantly declined over the past 700 years. Over the last millennium, the pollen percentages and influxes of the Picea species ( P. glauca, P. mariana, P. rubens) (white, black, and red spruce), and Pinus strobus (eastern white pine) significantly increased. We showed that these shifts in forest composition are being driven by changes in regional climate. In addition to the pollen percentage changes, the Medieval Climate Anomaly (AD 800–1300) appeared as increased pollen influxes and the Dark Ages Cold Period (AD 400–700) and Little Ice Age (AD 1400–1800) appeared as decreased pollen influxes. The signal for human modification of the landscape first appeared at ~AD 1550–1650 as increases in Ambrosia (ragweed) and Poaceae (grasses) from possible Indigenous agriculture. The signal of European settler landscape modification appeared at ~AD 1770 as the beginning of a steep, “classic” Ambrosia rise. It intensified over the subsequent 250 years as further increases in non-arboreal pollen taxa and early successional Acer (maple) species. Microcharcoal analysis showed that fire was a re-occurring event in the sugar maple-basswood domain, but had little impact on forest composition.

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.…”