Increasing fire and the decline of fire adapted black spruce in the boreal forest

Jennifer L. Baltzer*, Nicola J. Day, Xanthe J. Walker, David Greene, Michelle C. Mack, Heather D. Alexander, Dominique Arseneault, Jennifer Barnes, Yves Bergeron, Yan Boucher, Laura Bourgeau-Chavez, Carissa D. Brown, Suzanne Carriere, Brian K. Howard, Sylvie Gauthier, Marc Andre Parisien, Kirsten A. Reid, Brendan M. Rogers, Carl Roland, Luc SiroisSarah Stehn, Dan K. Thompson, Merritt R. Turetsky, Sander Veraverbeke, Ellen Whitman, Jian Yang, Jill F. Johnstone

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Intensifying wildfire activity and climate change can drive rapid forest compositional shifts. In boreal North America, black spruce shapes forest flammability and depends on fire for regeneration. This relationship has helped black spruce maintain its dominance through much of the Holocene. However, with climate change and more frequent and severe fires, shifts away from black spruce dominance to broadleaf or pine species are emerging, with implications for ecosystem functions including carbon sequestration, water and energy fluxes, and wildlife habitat. Here, we predict that such reductions in black spruce after fire may already be widespread given current trends in climate and fire. To test this, we synthesize data from 1,538 field sites across boreal North America to evaluate compositional changes in tree species following 58 recent fires (1989 to 2014). While black spruce was resilient following most fires (62%), loss of resilience was common, and spruce regeneration failed completely in 18% of 1,140 black spruce sites. In contrast, postfire regeneration never failed in forests dominated by jack pine, which also possesses an aerial seed bank, or broad-leaved trees. More complete combustion of the soil organic layer, which often occurs in better-drained landscape positions and in dryer duff, promoted compositional changes throughout boreal North America. Forests in western North America, however, were more vulnerable to change due to greater long-term climate moisture deficits. While we find considerable remaining resilience in black spruce forests, predicted increases in climate moisture deficits and fire activity will erode this resilience, pushing the system toward a tipping point that has not been crossed in several thousand years.

Original languageEnglish
Article numbere2024872118
Pages (from-to)1-9
Number of pages9
JournalProceedings of the National Academy of Sciences of the United States of America
Volume118
Issue number45
DOIs
Publication statusPublished - 9 Nov 2021

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS. This synthesis is an outcome of a working group meeting held in Flagstaff, AZ in 2017, funded by NASA Arctic Boreal Vulnerability Experiment (ABoVE) Grant NNX15AT71A to M.C.M. with support from the Bonanza Creek Long Term Ecological Research (BNZ LTER) program funded by NSF (DEB-1636476) and the US Department of Agriculture Forest Service (RJVA-PNW-01-JV-11261952-231). Additional, project-specific funding sources not already acknowledged in the references in SI Appendix, Table S1 are NASA ABoVE Grant NNX15AU56A to B.M.R., NSF Office of Polar Programs Grant 1708307 to H.A., and Fonds de recherche du Québec Nature and Technologies Concerted-Action Grant to L.S. Dedicated research time for J.L.B. was provided by the Canada Research Chairs program. We thank B. Lee and Cryo-dragon Inc. for graphic arts services.

Publisher Copyright:
© 2021 National Academy of Sciences. All rights reserved.

Keywords

  • Climate change
  • Ecological state change
  • Resilience
  • Tree regeneration
  • Wildfire

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