Expansion of high-latitude deciduous forests driven by interactions between climate warming and fire


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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Fig. 1: The model broadly reproduced the current tree composition of the Alaskan boreal forest.
Fig. 2: Modelled post-fire trajectories under the twentieth century climate differed from those under the twenty-first century climate.
Fig. 3: Deciduous broadleaf trees become dominant around 2058 because of interactions between increased soil temperatures, mineralization and fire.
Fig. 4: Deciduous broadleaf trees increase and evergreen conifer trees decrease in interior Alaska by 2100 because of warming and fire in the boreal forest.

Data availability

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).

Author information




All authors contributed to this work. Z.A.M., W.J.R. and J.T.R. designed the model experiments and implementation of regional fire regime. Z.A.M performed the simulations and analysed the results. Z.A.M., W.J.R., J.T.R., R.F.G. and B.M.R. contributed extensively to the contents of the manuscript.

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Correspondence to Zelalem A. Mekonnen.

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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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Supplementary Information

Supplementary Information I (Supplementary Figs. 1–14, Supplementary Tables 1–4 and Supplementary References) and Supplementary Information II (model development and definition of variables, and Supplementary References).

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Mekonnen, Z.A., Riley, W.J., Randerson, J.T. et al. Expansion of high-latitude deciduous forests driven by interactions between climate warming and fire. Nat. Plants 5, 952–958 (2019). https://doi.org/10.1038/s41477-019-0495-8

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