November already and as we lose an hour with the clocks back to GMT times for another six months, it now seems to darken very early. I used to worry, as a very young lad in late October, if it would be dark enough for fireworks at 7.30pm (my usual bedtime) by November 5th, but it always was! Something else I recall is that by then we would have gathered up huge piles of leaves ready to burn on the nights bonfire but recently many trees still seem yet to have shed their leaves by this date. So are we really seeing later leaf fall or is my old memory playing tricks?

Well, official research does seem to suggest that over the last thirty years, leaves have started to change colour and fall later in the year, a phenomenon that scientists now attribute directly to rising levels of atmospheric carbon dioxide.

Gail Taylor from the University of Southampton and her colleagues studied the growth and leaf fall of Populus trees (a genus which includes the poplar tree). The trees were grown in plots under either current or elevated atmospheric carbon dioxide levels and their colour was monitored using remotely sensed images of 'canopy greenness.' Leaves turned yellow later in the year under higher carbon dioxide concentrations, even when exposed to the same temperatures. The researchers think that the change in leaf colour is probably due to the effect of carbon dioxide on plant physiology.

Whereas we know that the earlier springtime leaf growth is strongly related to temperature, the belated autumn leaf fall is not in fact as even in our colder Autumns the leaves are falling later. However, deciduous trees are staying greener for longer than they were 30 years ago owing to the earlier arrival of new leaves and these later leaf falls. Which means later raking in the garden, well into December. However, there is also a suggestion by some horticulturalists that as many gardeners have given up on their seasonal gardening by then, leaves are getting left now to mulch and rot 'in situ' over the winter and spring. This allows some space for some animals to hiberate in as well as a better natural garden compost, so enriching the soil naturally, so in fact on some levels it may not be such a bad thing after all. Every cloud has a silver lining and all that..