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Behnaz Pirzamanbein . Photo

Behnaz Pirzamanbin

Associate senior lecturer

Behnaz Pirzamanbein . Photo

Holocene land cover change in North America : Continental trends, regional drivers, and implications for vegetation-atmosphere feedbacks

Author

  • Andria Dawson
  • John W Williams
  • Marie-José Gaillard-Lemdahl
  • Simon J. Goring
  • Behnaz Pirzamanbein
  • Johan Lindström
  • R. Scott Anderson
  • Andrea Brunelle
  • David Foster
  • Konrad Gajewski
  • Daniel G. Gavin
  • Terri Lacourse
  • Thomas A. Minckley
  • Wyatt Oswald
  • Bryan Shuman
  • Cathy Whitlock
Show all

Summary, in English

Land cover governs the biogeophysical and biogeochemical feedbacks between the land surface and atmosphere. Holocene vegetation-atmosphere interactions are of particular interest, both to understand the climate effects of intensifying human land use and as a possible explanation for the Holocene temperature conundrum, a widely studied mismatch between simulated and reconstructed temperatures. Progress has been limited by a lack of data-constrained, quantified, and consistently produced reconstructions of Holocene land cover change. As a contribution to the Past Global Changes (PAGES) LandCover6k Working Group, we present a new suite of land cover reconstructions with uncertainty for North America, based on a network of 1445 sedimentary pollen records and the REVEALS pollen-vegetation model (PVM) coupled with a Bayesian spatial model. These spatially comprehensive land cover maps are then used to determine the pattern and magnitude of North American land cover changes at continental to regional scales. Early Holocene afforestation in North America was driven by rising temperatures and deglaciation, and this afforestation likely amplified early Holocene warming via the albedo effect. A continental-scale mid-Holocene peak in summergreen trees and shrubs (8.5 to 4 ka) is hypothesized to represent a positive and understudied feedback loop among insolation, temperature, and phenology. A last-millennium decrease in summergreen trees and shrubs with corresponding increases in open land was likely driven by a spatially varying combination of intensifying land use and neoglacial cooling. Land cover trends vary within and across regions, due to individualistic taxon-level responses to environmental change. Major species-level events, such as the mid-Holocene decline in Tsuga canadensis (eastern hemlock), may have altered regional climates. The substantial land cover changes reconstructed here support the importance of biogeophysical and biogeochemical vegetation feedbacks to Holocene climate-carbon dynamics. However, recent model experiments that invoke vegetation feedbacks to explain the Holocene temperature conundrum may have overestimated land cover forcing by replacing Northern Hemisphere grasslands >30° N with forests, an ecosystem state that is not supported by these land cover reconstructions. These Holocene reconstructions for North America, along with similar LandCover6k products now available for other continents, serve the Earth system modeling community by providing better-constrained land cover scenarios and benchmarks for model evaluation, ultimately making it possible to better understand the regional- to global-scale processes driving Holocene land cover, carbon cycle, and climate dynamics.

Department/s

  • Department of Statistics
  • MERGE: ModElling the Regional and Global Earth system
  • eSSENCE: The e-Science Collaboration
  • LTH Profile Area: Aerosols
  • BECC: Biodiversity and Ecosystem services in a Changing Climate
  • Mathematical Statistics
  • LU Profile Area: Nature-based future solutions

Publishing year

2025-11-06

Language

English

Pages

2031-2060

Publication/Series

Climate of the Past

Volume

21

Issue

11

Document type

Journal article

Publisher

Copernicus GmbH

Topic

  • Climate Science
  • Other Mathematics

Status

Published

ISBN/ISSN/Other

  • ISSN: 1814-9332