Preprints
https://doi.org/10.5194/cp-2024-6
https://doi.org/10.5194/cp-2024-6
20 Feb 2024
 | 20 Feb 2024
Status: a revised version of this preprint is currently under review for the journal CP.

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

Andria Dawson, John W. Williams, Marie-José Gaillard, Simon J. Goring, Behnaz Pirzamanbein, Johan Lindstrom, R. Scott Anderson, Andrea Brunelle, David Foster, Konrad Gajewski, Dan G. Gavin, Terri Lacourse, Thomas A. Minckley, Wyatt Oswald, Bryan Shuman, and Cathy Whitlock

Abstract. 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 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 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 seasonality. A last-millennium decrease in summergreen trees and shrubs with corresponding increases in open land likely was 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 of eastern hemlock, may have altered regional climates. The substantial land-cover changes reconstructed here support the importance of biogeophysical vegetation feedbacks to Holocene climate dynamics. However, recent model experiments that invoke vegetation feedbacks to explain the Holocene Conundrum may have overestimated the 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 dynamics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Andria Dawson, John W. Williams, Marie-José Gaillard, Simon J. Goring, Behnaz Pirzamanbein, Johan Lindstrom, R. Scott Anderson, Andrea Brunelle, David Foster, Konrad Gajewski, Dan G. Gavin, Terri Lacourse, Thomas A. Minckley, Wyatt Oswald, Bryan Shuman, and Cathy Whitlock

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2024-6', Anonymous Referee #1, 04 Apr 2024
    • AC2: 'Reply on RC1', Andria Dawson, 16 May 2024
  • RC2: 'Outstanding achievement; a few points require further clarification and improved presentation', Jed Kaplan, 06 Apr 2024
    • AC1: 'Reply on RC2', Andria Dawson, 16 May 2024
Andria Dawson, John W. Williams, Marie-José Gaillard, Simon J. Goring, Behnaz Pirzamanbein, Johan Lindstrom, R. Scott Anderson, Andrea Brunelle, David Foster, Konrad Gajewski, Dan G. Gavin, Terri Lacourse, Thomas A. Minckley, Wyatt Oswald, Bryan Shuman, and Cathy Whitlock

Model code and software

Project workflow in R Andria Dawson et al. https://github.com/andydawson/reveals-na

Neotoma Lake Size Workflow Simon Goring et al. https://github.com/NeotomaDB/neotoma_lakes

Andria Dawson, John W. Williams, Marie-José Gaillard, Simon J. Goring, Behnaz Pirzamanbein, Johan Lindstrom, R. Scott Anderson, Andrea Brunelle, David Foster, Konrad Gajewski, Dan G. Gavin, Terri Lacourse, Thomas A. Minckley, Wyatt Oswald, Bryan Shuman, and Cathy Whitlock

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Short summary
Holocene vegetation-atmosphere interactions provide insight into intensifying land use impacts and the Holocene Conundrum- a mismatch between data- and model- inferred temperature. Using pollen records and statistical modeling, we reconstruct Holocene land cover for North America. We determine patterns and magnitudes of land cover changes across scales. We attribute land cover changes to ecological, climatic, and human drivers. These reconstructions provide benchmarks for Earth System Models.