Postglacial vegetation history related to temperate species (yellow birch and white pine) in a mixed boreal forest in Quebec

English Abstract:

Our knowledge about the postglacial vegetation history of the central portion of the balsam fir (Abies balsamea)-paper birch (Betula papyrifera) bioclimatic domain in Quebec remains fragmentary. The Haute-Mauricie region is of particular interest due to the presence of small forest stands dominated by yellow birch (Betula alleghaniensis) with the occasional presence of white pine (Pinus strobus), two temperate species located beyond their continuous and contemporary distribution range. A paleoecological study was conducted to reconstruct the main phases of the regional vegetation history in order to determine whether these species represents a priority for biodiversity preservation within an ecosystem-based management approach. We tested the hypothesis that yellow birch and white pine were more abundant during the Holocene climatic optimum, and that their distribution range was subsequently fragmented during the Neoglacial period. The distribution of yellow birch and white pine was first mapped over an area of 2000 km². Pollen analysis of a non forested peatland as well as pollen and macrofossil analysis of a thick forest humus from a forest stand were then conducted. The peatland and humus yielded temporal sequences of respectively 7940 and 2830 years. The results show that a balsam fir forest was present regionally 8000 years ago. Around 7500 BP, white pine and yellow birch were more abundant under a relatively warm climate. An increase in abundance of certain boreal species (Picea mariana, Pinus banksiana) and Betula papyrifera occurred during the Late Holocene. Our results suggest that the continuous distribution range of yellow birch and white pine once extended farther north than it does today, becoming fragmented during the Late Holocene. Today’s patches therefore represent remnants of an early to mid-Holocene temperate forest, and hence an important component of the region’s biodiversity that must be considered in ecosystem-based management plans.