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Low-elevation forest extent in the western United States constrained by soil surface temperatures

Nature Geoscience volume 17, pages 1249–1253 (2024)Cite this article

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Abstract

Climate change and disturbance threaten forested ecosystems across the globe. Our ability to predict the future distribution of forests requires understanding the limiting factors for regeneration. Forest canopies buffer against near-surface air temperature and vapour pressure deficit extremes, and ongoing losses of forest canopy from disturbances such as wildfire can exacerbate climate constraints on natural regeneration. Here we combine experimental, empirical and simulation-based evidence to show that soil surface temperatures constrain the low-elevation extent of forests in the western United States. Simulated potential soil surface temperatures predict the position of the low-elevation forest treeline, exhibiting temperature thresholds consistent with field and laboratory studies. High-resolution historical and future surface temperature maps show that 107,000–238,000 km2 (13–20%) of currently forested area exceeds the critical thermal threshold for forest regeneration and this area is projected to more than double by 2050. Soil surface temperature is an important physical control on seedling survival at low elevations that will likely be an increasing constraint on the extent of western United States forests as the climate warms.

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Fig. 1: SST response functions.
Fig. 2: Soil surface temperatures contain low elevation forests.
Fig. 3: Projected change in modelled forest cover between 1982–2018 and 2050.

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Data availability

All data that support the findings of this study are openly available at the references provided. New and derived datasets, including seedling experiments and 30 m gridded surface temperature predictions, are available via Figshare at https://doi.org/10.6084/m9.figshare.26950843 (ref. 51).

Code availability

The data and code that support the findings of this study are available via Figshare at https://doi.org/10.6084/m9.figshare.26950843 (ref. 51).

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Acknowledgements

Computational resources from the University of Montana’s Computational Ecology Lab, NASA Pleiades HPC cluster and the Griz Shared Computing Cluster contributed to this research (NSF award numbers 2018112 and 1925267). We thank the editors and three anonymous reviewers for comments and feedback that improved the final manuscript. We thank the Montana Climate Office for access to soil moisture observations. This work was supported with funding from the National Aeronautical and Space Administration (grant 80NSSC19K00181) and the USDA NIFA (grant 2022-67019-36438).

Author information

Authors and Affiliations

  1. USDA Forest Service Rocky Mountain Research Station, Missoula, MT, USA

    Zachary A. Holden

  2. Franke College of Forestry and Conservation, University of Montana, Missoula, MT, USA

    Solomon Z. Dobrowski & Zachary Hoylman

  3. Department of Community and Public Health Sciences, University of Montana, Missoula, MT, USA

    Alan Swanson & Allen Warren

  4. Montana Climate Office, Franke College of Forestry and Conservation, University of Montana, Missoula, MT, USA

    Zachary Hoylman

  5. Washington Department of Natural Resources, Olympia, WA, USA

    Drew Lyons

  6. Geosciences Department, University of Montana, Missoula, MT, USA

    Marco Maneta

Authors
  1. Zachary A. Holden
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  4. Zachary Hoylman
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Contributions

Z.A.H., S.Z.D. and M.M. designed the research. Z.A.H., D.L., A.S., A.W. and S.Z.D. performed the research and data analysis. S.Z.D, Z.A.H., Z.H., M.M. and A.S. wrote the manuscript. All authors contributed to revising the final manuscript.

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Correspondence to Zachary A. Holden.

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Nature Geoscience thanks Courtney Collins, Florian Zellweger and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Xujia Jiang, in collaboration with the Nature Geoscience team.

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Supplementary methods, Figs. 1–12 and Tables 1–5.

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Holden, Z.A., Dobrowski, S.Z., Swanson, A. et al. Low-elevation forest extent in the western United States constrained by soil surface temperatures. Nat. Geosci. 17, 1249–1253 (2024). https://doi.org/10.1038/s41561-024-01577-0

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