Susan J. Meades wrote:
>> Hi,
>> One of my students noticed that although most of the sugar maples here
> in northern Ontario have turned gold and red (and have since dropped
> their leaves), some of the sugar maples in town are still green. Someone
> told her that it was due to the trunks being damaged, but I think it
> probably is the source of these maples. Trees planted in the city are
> often garden stock from southern Ontario, where leaves don't turn as
> early (southern ecotypes). We've already had several frosts and 10 cm
> of snow last week, so these city maples now have dead green leaves
> hanging from the twigs. Does anyone have an accurate explanation for
> this phenomenon?
>> Thanks,
>> Sue Meades
> Sault Ste. Marie, ON
One possibility is that the trees growing in the city are exposed to
street lamps that are artificially extending the daylength. Fall leaf
abscission and senescence is a short-day, photoperiodically induced
phenomenon, and is only hastened by low temperatures.
Gerald F. Deitzer
University of Maryland
