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.
In a study published in Ecology and Evolution, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators synthesized data from 57 published studies spanning 1974 to 2024, encompassing 277 forest sites across the northern boreal zone. Using generalized additive models and CMIP6 climate projections (SSP2-4.5 and SSP5-8.5), they examined how litterfall production varies among plant functional types—deciduous, evergreen, and mixed forests—and how it responds to stand age, temperature, and precipitation.
They found that boreal forests produce an average of 1,959 kg of litterfall per hectare per year, with deciduous forests outperforming evergreen stands. Litterfall in evergreen and mixed forests followed a hump-shaped relationship with stand age, peaking at about 60 years for evergreens and 150 years for mixed forests, then declining. Deciduous forests showed no significant age-related trend.
Critically, they identified a temperature threshold for evergreen forests: litterfall increased with mean annual temperature up to about 5°C, beyond which it plateaued. Deciduous and mixed forests did not exhibit a clear temperature threshold in the main model, though separate climate-focused analyses revealed more complex responses.
“Lower litterfall production may limit soil organic carbon accumulation, while higher temperatures accelerate soil respiration,” said the researchers. “Together, these processes may weaken the boreal carbon sink and contribute to positive climate feedbacks.”
Their findings highlight the importance of accounting for PFTs and physiological thresholds when investigating the litterfall dynamics in forests and the potential impact of climate warming on the contribution of litterfall to carbon and nutrient cycling.
