High-latitude regions have experienced rapid warming in recent decades, and this trend is projected to continue over the twenty-first century1. Fire is also projected to increase with warming2,3. We show here, consistent with changes during the Holocene4, that changes in twenty-first century climate and fire are likely to alter the composition of Alaskan boreal forests. We hypothesize that competition for nutrients after fire in early succession and for light in late succession in a warmer climate will cause shifts in plant functional type. Consistent with observations, our ecosystem model predicts evergreen conifers to be the current dominant tree type in Alaska. However, under future climate and fire, our analysis suggests the relative dominance of deciduous broadleaf trees nearly doubles, accounting for 58% of the Alaska ecosystem’s net primary productivity by 2100, with commensurate declines in contributions from evergreen conifer trees and herbaceous plants. Post-fire deciduous broadleaf tree growth under a future climate is sustained from enhanced microbial nitrogen mineralization caused by warmer soils and deeper active layers, resulting in taller trees that compete more effectively for light. The expansion of deciduous broadleaf forests will affect the carbon cycle, surface energy fluxes and ecosystem function, thereby modifying important feedbacks with the climate system.
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Data products in this study are archived at http://ngee-arctic.ornl.gov. Additional data that support the findings of this study can be found from the corresponding author upon request.
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This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory as part of the Next-Generation Ecosystem Experiments in the Arctic (NGEE-Arctic) project and the RUBISCO Scientific Focus Area. B.M.R. was funded by NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE) and Carbon Cycle Science programmes (NNX17AE13G).
The authors declare no competing interests.
Peer review information: Nature Plants thanks Emeline Chaste and Winslow Hansen and other, anonymous, reviewers for their contribution to the peer review of this work.
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