It might seem obvious that it’s the changing season that triggers the shift in leaf colour in forests, but new research in Nature Climate Change shows that it’s a bit more complicated. Wu and colleagues studied sites in China and the USA using satellite images, laser scanning technology, and temperature sensors to study autumn leaf changes. They found that denser forests with taller trees showed different timing in leaf colour changes compared to more open forests. It’s not just an aesthetic matter. The timing of leaf changes affects how effectively they can capture carbon.
Wu and colleagues found that autumn came later to denser forests. Part of this is due to forests creating an environment, with denser forests creating more stable temperatures and reduced light levels for trees growing underneath. Light was particularly important with light levels having a stronger effect on when leaves started changing colour than temperature differences. This means that understorey trees are affected the most by forest structure.
The data came from satellite images, that could track the colour of forests on an almost daily basis. They combined this with airborne laser scanning to calculate the forest height and density. Finally, temperature sensors were placed at different heights in the forests to measure how forest structure affected local climate. All put together this allowed them to track what changed when autumn came.
Wu and colleagues see their work as a companion to work on spring phenology where people track leaf-out and the greening of the forest. Autumn, they argue is less studied. People know that temperature and day length matter, but Wu and colleagues were also looking to explain local variations. Understanding these variations could help plug gaps in future climate models.
Wu, X., Niu, C., Liu, X., Hu, T., Feng, Y., Zhao, Y., Liu, S., Liu, Z., Dai, G., Zhang, Y., Van Meerbeek, K., Wu, J., Liu, L., Guo, Q., & Su, Y. (2024). Canopy structure regulates autumn phenology by mediating the microclimate in temperate forests. Nature Climate Change. https://doi.org/10.1038/s41558-024-02164-2
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