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Tt: Re: When the leaves fall
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> From: "Mark Stephens" <marks@entekird.com>
> To: "Community_Forestry" <Treetown@Majordomo.Flora.Com>
> Date: Tue, 14 Oct 1997 07:53:25 -0400
> -----------------------------------------------------------------------
> <snip>
> Why leaves fall at different times? Cultivars come from all over the US
> and Canada. I would _guess_ they are on their own schedule. <snip>
I would tend to agree with the "origin of the cultivars" hypothesis. Our
town has an excessive number of Norway maples, and each of the cultivars
seems to have its own timing. Some have already turned and fallen but the
almost all specimens of the most common cultivar still have green leaves.
> From: RT Ellsberry <rtells@Flora.Com>
> To: Community Forestry <Treetown@Majordomo.Flora.Com>
> Cc: Michael Laurenson <EmElle@HarbourMoon.Ca>
> Date: Tuesday, October 14, 1997 12:32 AM
> Subject: Tt: When the leaves fall ...
>
> > ----------------------------------------------------------------------
> <snip>
> > But first this
> > digression: Fall color is itself a beautiful and complex bio-
> > chemical phenomenon, made all the more fascinating when one
> > concludes that foliage color probably provides no knowable
> > evolutionary advantage for a tree -- that it's simply a lucky
> > (for us) side-effect of other processes ... or is it ?
In fact, there probably are evolutionary advantages for fall color change.
The yellow carotenoid pigments (accessory photosynthesis pigments that
increase the wavelengths of light usable by the plant) and brown
xanthophyll pigments are present in the leaf throughout the year but
hidden by all the chlorophyll. The breakdown and recycling of chlorophyll
in the fall allows the plant to recoup energy before leaf fall but also
allows the other pigments to be seen. Anthocyanins and betacyanins are
responsible for the red color-- sugar accumulation in the fall favors
their production though I'm not sure what, if any, their function is.
(Someone told me once they act as a UV-blocking "sunscreen" which the
leaves need once the chlorophyll is gone-- but please don't quote me on
this one.)
So... plants change color in the fall because it is energetically
beneficial to them. We get a great show as a by-product.
Marianna Wood
Biological and Allied Health Sciences
Bloomsburg Univeristy
Bloomsburg PA
PS-- I'm an animal ecologist. Perhaps someone more botanically inclined
could provide more or better details about fall color change; I'm always
looking for enlightenment!
References: