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Re: leaves



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> From: Bonnie Blackwell, x 3332 <bonn@qcvaxa.acc.qc.edu>
> To: dinosaur@usc.edu
> Subject: leaves
> Date: Wednesday, October 16, 1996 1:24 PM
> 
> I have always understood that shedding leaves by trees (and note that
> gingkoes do it too!!) is a response to cold weather.  whether this is
> true or not i am not sure, but if it is, then one would not
> expect the leaves to drop in the late K because temperatures even in
> places like alaska were too warm.  if, however, the dropping leaves
> is a response to either low light levels or drier conditions (which
> in winter come from having snow rather than rain), then we would
> expect leaves to have dropped, but not necessarily in the "autumn"
> as defined by astronomical definitions in the case of dryness.
> b

Bonnie:
Last year in West Virginia, we were "lucky' enough to have a hole in the
ozone over part  of our state for part of the summer. It was widely
reported, and there were several articles in the local papers. Anyway-
leaves turned brown-not red or yellow or anything but stayed on the trees
(for the most part) until autumn. This occured during the summer.  Two
young walking stick willows in my yard died as a result. I would be
interested in knowing whether or not this occurs in Tiera Del Fuego & Peru,
as I have read that they have an almost constant ozone hole overhead.

I have always understood that leaves change colors and drop off as a result
of trees pulling the chlorofil out of the leaves. A defense mechanism
against loosing their cache of food to freezing temperatures. What you are
left with is the part of the leave that wasn't  green to begin with- the
structural or skeletal part. 

Regardless of why they change colors, I think an important question to ask
is this: Do dead (brown,red, yellow, whatever) leaves have any nutritious
value?
Certainly, during periods when the Earth had more volcanic activity (
therefore more climatic differences) leaves might have died at  times other
that autumn.    

What would long necked herbiforous dinos have eaten if the leaves fell too
early? A review of current long necked herbivores (Girraffes, for example) 
might be in order. Can the forage from the ground sufficient to sustain
themselves?

Another question- aren't there some non-needle trees (Live Oaks might be a
good example) that don't loose their leaves in the autumn? I think that
they kind of shed year round, but may be mistaken.