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TT: RE: Fall color peaking in Baltimore

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 On Tue, 4 Nov 1997, Thomas W. Kimmerer wrote:

> ... The temperatures of this fall would tend to delay peak coloration.
> The onset of autumn, the withdrawal of nutrients from the leaves into
> the tree, is set by daylength, not by temperature (many ornamentals have
> odd coloration timing if they come from other latitudes).  However, the
> duration of leaf color change, and the interval between onset of autumn
> and leaf drop is a function of temperature, particularly of minimum
> night temperatures.  That's why cold, clear nights give us the most
> intense colors, and why New England has a "brighter" autumn than the
> South ...

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 I'm probably not the only one in TreeTown who thinks often about
 Tom Kimmerer's evocative commentaries on tree physiology.  Gary, I
 and other listees are (returning) students at Towson U., north of
 Baltimore, where we enjoy an astonishing 'academic forest' of
 well-cared-for and old-growth trees -- not being a true 'arboretum'
 campus (which could be the subject of another great thread :) ...

 OK, I'll break here for a moment.  Towson U. has awesome Sycamores,
 American Beeches, (Yellow) Tulip Poplars, mixed native Oaks & Maples
 which have, for a hundred years, had buildings and roads landscaped
 around them ! Plus a variety of 'introduced' ornamentals, particularly
 Japanese Red Maple (many colorful cultivars), European Beech, Japanese
 Zelkova, and one prominent, maturing specimen in the middle of campus
 which I think is a Bald-Cypress, but which Gary might correct me on.
 The Towson squirrels are more conspicuous than the birds, and much
 more numerous than the school mascot, which happens to be the tiger ...

 A walking tour of Towson U. is highly recommended, lacking perhaps
 in American Elms :( ... I've heard that there are also lots of Pecans,
 and I don't know if they are native or not, at least this far north.
 I haven't noticed many Magnolias.  Purple Norway Maples are also common.
 The forestry crews seem to keep the Ailanthus out pretty well (or is
 that a function of such broad diversity?)

 Apologies for making this so long.  Looking at the remaining leaves
 this time of year, it's obvious that bright sun hitting them ac-
 celerates (amplifies) their coloration.  Somehow the trees have a
 'memory' of the current climatic conditions (to borrow a computer
 term).  So what I'm wondering is, where are these 'memories' recorded?
 My naive guess is in the leaves themselves, that the biology of one
 single leaf triggers when it changes color and drops, independent of
 its peers.  Otherwise the entire tree, or at least large sections
 of it, would 'fall' all at the same time, which does not appear to
 be the case (for most resident deciduous species).

 Thanks for letting me go off so.  It's a beautiful autumn :) ...

 Richard@Flora.Com

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