Here are my SIMB photos for October. It has been a very curious few
weeks. As you can see, many leaves are still on our trees - the leaves are
only just falling off the trees, which by several accounts, is 7-10 days
late. This is especially evident if you compare these photos I am sending
to you with those from previous Octobers. Some of the trees - mostly the
aspen - still have many green leaves attached. Some of these trees are
actually loosing leaves but they are falling green, not the usual gold.
So what has been happening to cause this?
Here are some thoughts based on my discussions with various scientists. We
had a very late spring followed by an extremely hot and dry summer - broke
the record for the number of days exceeding 80F (26.6 C. I used F in this
case since the National Weather Service reports their recorded temperatures
in F). Then, starting around 15 August, we received a lot of rain.
According to my records, between 15 Aug - 15 Sep we received 86.4 mm of
rain! That is after only 42 mm of rain during 1 June - 15 Aug. This could
mean that after a very stressful summer of little production/ growth, the
trees, especially the aspen, were "making up" for lost time by keeping
their leaves longer than usual so they could continue to make sugar to
store for the winter. The reason some of the leaves are falling green is
that although the leaves are continuing to photosynthesize to produce
sugar, perhaps leaf abscission (creating a scar to pinch off nutrient
supply to the leaf and then the leaf falls) is triggered by photo period
and so the leaf falls while it is still green. This is all a guess but
perhaps explains why we are experiencing such a late leaf fall.
It has been quite lovely to have such a long and late autumn. We rarely get
to experience the fall colors for as long as we have this year.
