Climate Warming Will Reduce Boreal Forest Litterfall, but the Response Differs Among Plant Functional Types

ABSTRACT Boreal forests are critical carbon sinks increasingly threatened by climate change. More than two‐thirds of this boreal carbon is stored in soil and litter, highlighting the crucial role of litterfall for carbon and nutrient cycling. Boreal forests have stands of different plant functional types (deciduous, evergreen, and mixed), and we lack information on their contributions to litterfall production. This hinders our understanding of spatiotemporal variations in boreal litterfall production, and thus predictions under future climate scenarios. Here, we synthesized boreal litterfall data from published studies and applied generalized additive models to (1) examine stand age‐ and temperature‐related litterfall dynamics across plant functional types and (2) project future trends under climate change, using two climate scenarios CMIP6 climate scenarios (SSP2‐4.5 and SSP5‐8.5). Mean litterfall production was 1959 kg ha −1 year −1 , with deciduous forests showing the greatest litterfall production. Litterfall production increased with stand age, then declined, peaking at 60 years for evergreen forests and 150 years for mixed forests. Deciduous forests showed no significant age‐related trends in litterfall. Critical temperatures may affect litterfall production; for evergreen forests, the threshold is 5°C, above which litterfall production stabilized, with no threshold for deciduous nor mixed forests. The two CMIP6 climate scenarios predicted widespread declines in boreal litterfall production by the end of the 21st century. The decline in litterfall production was pronounced under SSP5‐8.5, with 70% of boreal forests projected to experience litterfall declines exceeding −20%. Synthesis: Our study highlights the importance of incorporating specific plant functional types and stand age dynamics in predictive models of litterfall production. The findings provide a robust foundation for predicting future changes in boreal litterfall production, thereby advancing the understanding of vegetation‐climate interactions in these forest ecosystems.