It had been assumed that a warming climate would lead to a longer growing season for our deciduous trees, followed by a later autumnal leaf-fall. However, research has indicated that this might not be so.
Researchers used leaf-fall data collected between 1948 and 2015, combined with the results from experiments examining the role that CO2 and sunlight play in leaf-fall’s timing, to model what would happen by the year 2100 if our carbon emissions stay as high as they are now.
The experiments and the 67-year tree record suggest that higher CO2 levels, temperatures and sunlight levels are driving the leaves to be more productive in spring and summer, but are actually hastening their demise and fall in autumn. The conclusion seems to be that deciduous trees have a limit to how productive they can be in a single growing season; if earlier springs bring trees into leaf sooner, that limit is also reached sooner, resulting in an earlier leaf-fall.
This year, some of the park’s oak trees have held on to their leaves right to the end of November. These experiments seems to imply that this is an aberration rather than the beginning of a trend, perhaps the result of 2020’s exceptionally wet summer and below average levels of sunshine.
All images taken in the park by DKG.