Climate change is increasing the intensity and frequency of extreme heat events. Ecological responses to extreme heat will depend on vegetation physiology and thermal tolerance. Here we report that Larix sibirica, a foundation species across boreal Eurasia, is vulnerable to extreme heat at its southern range margin due to its low thermal tolerance (Tcrit of photosynthesis: ~ 37–48 °C). Projections from CMIP6 Earth System Models (ESMs) suggest that leaf temperatures might exceed the 25th percentile of Larix sibirica's Tcrit by two to three days per year within the next two to three decades (by 2050) under high emission scenarios (SSP3-7.0 and SSP5-8.5). This degree of warming will threaten the biome's continued ability to assimilate and sequester carbon. This work highlights that under high emission trajectories, we may approach an abrupt ecological tipping point in southern boreal Eurasian forests substantially sooner than ESM estimates that do not consider plant thermal tolerance traits.

Data can be opened using a text editor or Microsoft Excel. Codes can be opened using a mix of R, Matlab, and Python.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: 1737788Funding provided by: National Oceanic and Atmospheric AdministrationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000192Award Number: NA18NWS4620043BFunding provided by: H2020 Marie Skłodowska-Curie ActionsCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010665Award Number: 101031748Funding provided by: National University of MongoliaCrossref Funder Registry ID: http://dx.doi.org/10.13039/100016993Award Number: P2019-3634Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: OISE-1743738

Ecophysiological data were collected using a Jr. PAM Chlorophyll Fluorometer and a mass spectrometer. Climate model data comes from CMIP6.