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Even modest climate change may lead to major transitions in boreal forests


The sensitivity of forests to near-term warming and associated precipitation shifts remains uncertain1,2,3,4,5,6,7,8,9. Herein, using a 5-year open-air experiment in southern boreal forest, we show divergent responses to modest climate alteration among juveniles of nine co-occurring North American tree species. Warming alone (+1.6 °C or +3.1 °C above ambient temperature) or combined with reduced rainfall increased the juvenile mortality of all species, especially boreal conifers. Species differed in growth responses to warming, ranging from enhanced growth in Acer rubrum and Acer saccharum to severe growth reductions in Abies balsamea, Picea glauca and Pinus strobus. Moreover, treatment-induced changes in both photosynthesis and growth help explain treatment-driven changes in survival. Treatments in which species experienced conditions warmer or drier than at their range margins resulted in the most adverse impacts on growth and survival. Species abundant in southern boreal forests had the largest reductions in growth and survival due to climate manipulations. By contrast, temperate species that experienced little mortality and substantial growth enhancement in response to warming are rare throughout southern boreal forest and unlikely to rapidly expand their density and distribution. Therefore, projected climate change will probably cause regeneration failure of currently dominant southern boreal species and, coupled with their slow replacement by temperate species, lead to tree regeneration shortfalls with potential adverse impacts on the health, diversity and ecosystem services of regional forests.

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Fig. 1: Cumulative survival (percent) to 2016 by species and warming and rainfall treatments, averaged across sites and seedling cohorts.
Fig. 2: Growth (stem biomass per plant in 2016) by species and warming and rainfall treatments, averaged across sites and seedling cohorts.
Fig. 3: Relationships between climate treatment effects on different response metrics.
Fig. 4: Compositional pie charts for relative abundance in 2016 calculated from the stem biomass for each species relative to the total biomass of all species in the same treatment.
Fig. 5: Treatment temperature relative to temperature at the historic range margin influences species response to experimental warming.

Data availability

To create the panels of Extended Data Fig. 8, we used high-resolution gridded data of month-by-month variation in climate (January 1901–December 2020) from the Climatic Research Unit Time Series version 4.05 (CRU TS4.05), available at We also used species distribution data from the Climate Change Tree Atlas, available at (see refs. 39,40). The data used in the analyses of this work, as well as spreadsheets with the data used in the main-text and Extended Data figures, are available from the Data Repository for University of Minnesota (DRUM) at Source data are provided with this paper.


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We thank the many field assistants who were involved in implementing and maintaining the experimental facility, the experimental planting and the measurements presented in this paper. This research was supported by the US Department of Energy, Office of Science, and Office of Biological and Environmental Research award number DE‐FG02‐07ER64456; Minnesota Agricultural Experiment Station MN-42-030 and MN-42-060; the College of Food, Agricultural and Natural Resources Sciences and Wilderness Research Foundation, University of Minnesota; and the National Science Foundation, Biological Integration Institutes grant NSF-DBI-2021898.

Author information

Authors and Affiliations



P.B.R., R.A.M., S.E.H. and R.L.R. conceived and designed the original experiment. A.S., R.L.R., K.E.R. and R.B. collectively implemented the experiment; supervised or performed acquisition of all tree growth and survival data, as well as associated temperature and rainfall data; and curated all data. P.B.R. developed the idea for this study, carried out all analyses, constructed the figures and tables with assistance from R.B. and wrote the first draft. All authors contributed to the interpretation of the results and were involved in writing and editing subsequent drafts. P.B.R. and R.A.M. were responsible for acquiring the funding for the project, and P.B.R. was responsible for all project supervision and administration.

Corresponding author

Correspondence to Peter B. Reich.

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The authors declare no competing interests.

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Nature thanks Arun Bose and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Percent of individuals of the cohorts planted in 2012 and 2013 surviving over time, by species, warming, and rainfall treatments.

The cohorts were planted in the spring, and censused in the fall of that year and of each subsequent year. See Extended Data Table 4 for Wald test statistics. Sample sizes shown in Extended Data Table 3.

Source data

Extended Data Fig. 2 Growth (mean stem biomass per plant) over time by species and warming and rainfall treatments for plants of the 2012 and 2013 cohorts.

The cohorts were planted in spring, and censused in the fall of the same year and fall of each subsequent year. Each point represents the mean stem biomass per plant (± SE) of the survivors. Sample sizes shown in Extended Data Table 3.

Source data

Extended Data Fig. 3 Warming response of biomass growth in relation to warming response of survival.

Relationship among species of the percent change in cumulative stem biomass growth in + 3.1 °C warming (relative to biomass in ambient temperatures) to the percent change in cumulative survival in + 3.1 °C warming (relative to survival in ambient temperatures) for years 2013–2016 for plants in ambient rainfall treatments. Each line represents the regression for a different year; the fits are not intended to convey a biological function but to illustrate the association of growth and survival. The pointed–gray horizontal line represents the average growth for ambient temperature plants considered as reference for growth. Relationships were similar (i.e., growth and survival responses compared to ambient grown plants were positively associated) for plants in low rainfall treatment and for plants in the intermediate warming treatment. Sample sizes shown in Extended Data Table 3.

Source data

Extended Data Fig. 4 Relationship between warming response and species latitude.

Relationships between the percent change in cumulative survival or cumulative biomass growth in + 3.1 °C treatment relative to ambient temperature treatment for plants in ambient rainfall treatment (as in Extended Data Fig. 3) and latitude for years 2013–2016. In each row, different symbols (corresponding to those used in Extended Data Fig. 3) represent the different years. Each point within a panel represents a species according to their geographic center of latitudinal distribution in central North America23. From left to right: Acer rubrum, Quercus rubra, Quercus macrocarpa, Acer saccharum, Pinus strobus, Betula papyrifera, Abies balsamea, Pinus banksiana, and Picea glauca. Each line represents the regression for a different year; the fits are not intended to convey a biological function but to illustrate the association of growth or survival response to warming with species distributions. The pointed–gray line represents the average growth for ambient temperature plants considered as reference for growth. Relationships were similar (i.e., growth and survival responses compared to ambient grown plants were both associated with species distributions) for plants in low rainfall treatment and for plants in the intermediate warming treatment. Sample sizes shown in Extended Data Table 3.

Source data

Extended Data Fig. 5 Relationship between photosynthetic response to warming and species stomatal sensitivity to soil moisture.

Relationships between change in net photosynthesis due to climate treatments and (left) the sensitivity of stomatal conductance to soil moisture for nine species in two different rainfall regimes and (right) the sensitivity of stomatal limitation to VWC for nine species in two different rainfall regimes. For both x–axes we use the slope of the relevant metric versus VWC. For net photosynthesis measured on plants in + 3.1 °C warming in both ambient and reduced rainfall, the effects are characterized as the change relative to plants in the ambient temperature–ambient rainfall plots. Lines and 95% confidence intervals shown for either linear correlation or logarithmic fits. Sample sizes for the different species and treatments showing the values for ambient rainfall followed by the reduced rainfall treatment: A. balsamea (85, 65), A. rubrum (160, 156), A. saccharum (164, 160), B. papyrifera (156, 146), P. glauca (138, 128), P. banksiana (119, 115), P. strobus (136, 136), Q. macrocarpa (160, 162) and Q. rubra (166, 166).

Source data

Extended Data Fig. 6 Stem mass in relation to climate treatments.

Stem mass per unit ground area (combines survival and growth) by species and warming and reduced rainfall treatments in 2016. Error bars show ± SE calculated from the data aggregated by plot (n = 6). Sample sizes shown in Extended Data Table 3.

Source data

Extended Data Fig. 7 Warming response in relation to species abundances.

Effects of warming and rainfall treatments on different response metrics in relation to species relative abundance in northeastern Minnesota, USA. For growth, survival and photosynthesis measured on plants in + 1.6 °C, + 3.1 °C warming in both ambient and reduced rainfall, the effects are characterized as the change relative to plants in the ambient temperature, ambient rainfall plots. Total number of individuals per species in 2019 is across all U.S. FIA plots in the MNDNR Ecological Classification System Zone 212 (which covers most of northeastern Minnesota). The sample sizes are the same as described in the Fig. 3 for the middle and bottom row panels.

Source data

Extended Data Fig. 8 Location of average experimental treatment climate in relation to the climate range of each species.

Each panel corresponds to one experimental species and the contour lines contain the average May 1st to September 30th precipitation and temperature conditions of the 95% central points extracted from the 0.5º pixels climate dataset of the mid–continental range39 (88º W–98º W) of North America that overlaps with the range of each species shown in the North America atlas40. Each contour represents the average of 30 years and they are calculated for every period from the most recent (1991–2020) to as far back as 1941–1970. The data points show the mean 5–year average May 1st–September 30th rainfall and temperature for each climate treatment at each site.

Source data

Extended Data Table 1 Description of the environmental conditions related to the experimental treatments
Extended Data Table 2 Information about the species used in this experiment
Extended Data Table 3 Replications for each combination of species and treatments used in the experiment
Extended Data Table 4 Modeled proportional hazards for survival and growth for the experimental treatments
Extended Data Table 5 Results for the Wald test for survival of individuals planted in the cohorts of 2012 and 2013

Supplementary information

Source data

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Reich, P.B., Bermudez, R., Montgomery, R.A. et al. Even modest climate change may lead to major transitions in boreal forests. Nature 608, 540–545 (2022).

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