Delayed autumn senescence

from https://www.flickr.com/photos/andrewsteele/4082262513https://www.flickr.com/photos/andrewsteele/4082262513

The growing season at mid-to-high latitudes has been lengthening as a result of climate change. This is primarily due to an advancement of spring, but it's also partly due to a delay in autumn phenologies (IPCC, 2007). Indeed, we're having quite a mild autumn this year, and it seems natural to conclude that this would cause leaves to retain their leaves for longer, and to change colour later. However, changes in autumn phenologies are less well understood than spring ones. I touched on this in my previous post. Advancing spring phenologies correlate well with rising temperatures, but delayed autumn phenologies correlate less well, which implies that there are other factors playing a role.

Similarly to some instances of bird migration and mammal hibernation, in many trees, growth cessation, the first stage in winter dormancy, is initiated by day length (Wareing, 1956). It was thought that Populus' autumn phenologies are controlled by photoperiod. But Taylor et al. (2007) performed an experiment where Populus trees were grown with elevated CO2 (550ppm, we're now at ~400ppm) and found that this delays autumn leaf colour changes and leaf fall. Rhode at al. (2011) found that Populus trees also found that temperature had an effect. However, these studies are all done on one species and it's fairly certain that there will be species-specific responses to the same environmental changes.