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fall leaf color

Rod Savidge savidge at unb.ca
Mon Nov 15 15:30:00 EST 1999

At 02:50 PM 14/11/1999 GMT, you wrote:
>Does anyone know why one tree can have an assortment of fall leaf color
(on one
>individual, that is)? Sugar Maple, for example, can go the spectrum from
>to deep red. Any answers?

Dear Kellie,

Aesthetics is one of many areas in forestry receiving zilch for financial
support.  Consequently, there isn't really very much known with any
certainty.  Piecing various pieces of physiological information together,
my thinking (essentially a hypothesis) is that the primary factor
determining variation within the individual tree is water availability.
Photoperiod (short days) seems to be the primary trigger for leaf colour
change, but cool nights (presumably for starch hydrolysis) and warm days
(elevated metabolism) are also important for anthocyanin biosynthesis, not
so critically important for green chlorophylls to degrade to yellow
carotenoids.  Starch hydrolysis and metabolism in general are a function of
water potential in (i.e., water availability to) the leaves.   The most
brilliant and varied autumn colours always are found when the soil has been
recharged with water in late summer - early autumn.   If you study old
maple trees carefully, you will see that each major branch appears to be
linked to a major root (often times this can be readily seen in terms of
spiralling in the stem axis linking branches to roots).  Presumably, some
roots are in soil better enriched in water than others.  Also, when
comparing individual leaves on a single branch, it is possible that some
leaves have greater osmotic potential thus greater ability to pull in water
than others.  

   Rod Savidge, PhD, Professor       |         E-mail: savidge at unb.ca
   Faculty of Forestry and          \|/
   Environmental Management       \  |  /      Phone:  (506) 453-4919
   University of New Brunswic     _\/|\/_
   Fredericton, NB CANADA           \|/        Fax:    (506) 453-3538
   E3B 6C2                           |

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