Scientists have uncovered the mechanism by which temperate forest canopy structure influences autumn phenology, providing a scientific foundation for predicting how autumn phenology will respond to climate change and its impact on the forest's carbon sequestration capacity.

Autumn phenology refers to the seasonal changes in organisms, such as plants and animals, during autumn, influenced by factors like temperature, light and precipitation.

Studying autumn phenology is essential for understanding the effects of climate change, assessing ecosystem health, and predicting species' adaptability.

While previous research has generally indicated that macroclimate is the primary driver of temporal and spatial variation in autumn phenology, significant local differences in the phenology of the same tree species can still occur, even in areas with similar macroclimatic conditions. The mechanisms behind this local variation in temperate forests have remained unclear.

Researchers from the Institute of Botany under the Chinese Academy of Sciences studied six northern temperate forest sites, using laser radar and high spatiotemporal resolution imagery to quantify autumn phenology and canopy structure. They discovered a significant and consistent relationship between the two.

The canopy structure influences autumn phenology by regulating microclimate factors, such as radiation and temperature within the forest, according to Su Yanjun, a researcher at the institute.

"A complex canopy structure can, on one hand, weaken light penetration within the forest, reducing the intensity of photosynthesis and delaying the time at which plants reach carbon saturation," Su explained.

"On the other hand, it can enhance the buffering effect of temperature, slow down the rate of cold accumulated temperature and reduce the risk of plants from getting frost damage. All of these factors may delay the onset of autumn phenology," he added.

The study also found that incorporating the "canopy structure-microclimate-autumn phenology" mechanism into traditional phenology models significantly improves their predictive accuracy. Traditional models that exclude this mechanism often overestimate the effect of global warming on delaying autumn phenology.

The study was published in Nature Climate Change.