Sudden Ginkgo leaf fall

A number of people noticed this year that the leaves of ginkgo trees turned bright yellow, as usual, and then suddenly dropped all their leaves literally overnight leaving a golden carpet of leaves around the trees. This is actually pretty normal too, but usually it happens along with a lot of other trees dropping leaves, so fewer people notice.  2016 has been a long warmish fall with no good hard frosts before there was a very cold overnight freeze.  What happens is this. The shorter, cooler days stops the production of chlorophyll that ordinarily masks the yellow pigments (carotenoids, xanthophylls) and the leaves turn yellow. This is pretty common for lots of trees. At the base of the leaf stalk deciduous trees form a week place called an abscission zone, and in most trees a bit of back and forth bending in the wind causes the leaf to fall.  Gingko makes such a zone, but some of the vascular tissue remains connected and it takes a freeze, forming some ice crystals, to break the residual vascular connection, so after such a freeze, the leaves all fall at once. One day ginkgo trees have yellow leaves, the next day the trees are bare and the ground carpeted with ginkgo leaves. 

Suddenly deciduous

Last night it froze; the low temperature was 25 F.  Up until now only the lightest of frosts had happended, so lots of trees still have green leaves.  Under these circumstances a number of tree species will drop their leaves all at once including hackberry and black walnut, and most definitely ginkgo.  What causes tree leaves to drop is an abcission layer, an anatomically weak zone that forms in the fall at the base of the leaf stalk.  Trees like ginkgo still hang on to their leaves until a freeze, and then, perhaps as a result of ice crystal formation, the weak connection is broken and as the temperature goes up a few degrees, all the leaves fall at once.  TPP sort of wishes other trees did the same because then you'd be done with it, but some of our big trees hang on to leaves so tenaciously you end up raking in the spring.  The areas under the suddenly deciduous trees were just a carpet of dropped leaves this morning, and most people won't even notice. And leaves were still falling like rain.  Most other trees drop leaves more gradually as the abcission zone matures.  All trees drop leaves, but when they drop them all seasonally, they are deciduous.  Otherwise they are evergreen, which is not synonymous with conifers because some are deciduous.

Who took the preserved ginkgo?

Specimens are always a problem, and how can you teach students about organisms if you can't put the organism, or at least significant pieces thereof, into their hot little hands?  Let's say you want your students to understand the reproductive structures of a ginkgo, using them to compare to those of conifers, so you have to have specimens.  Now with this in mind, TPP had collected pollen cones and ovulate structures from ginkgo trees and preserved them in ethanol, two half gallon jars of pickled ginkgo, enough to last for years.  The other reason this is necessary is that ginkgo trees don't produce these structures except once a year, usually in the last week of the semester on average, and the lab class is always at a different time of year.  So you go to the cupboard, and there's only one jar; it says ovulate ginkgo on the lid's label, but it's actually pollen cones. Where the bloody hell is the other jar?  Someone used them, and accidentally switched the lids, but for reasons as yet undetermined, did not replace the other jar.  The problem with this is that by the time you figure this out, it's too late.  Even if this had been know at the beginning of the semester, it makes no difference because you can't just go out and buy pickled reproductive structures of ginkgo.  They're only good for just one thing, teaching, and nobody who teaches knows anything.  Something is very suspicious, very suspicious indeed.  There are only so many classes that would use such specimens, and only certain people instruct those classes, so the number of suspects is pretty finite.  Some wandering gypsies didn't make off with them and no ransom notes have been received.  Ginkgo?  Oh, yeah, them trees.  Seems my colleagues have pretty good alibis or very convenient memories.  Guess some things should be kept under lock and key, but TPP is just so trusting.  Now to remember that new specimens are needed when the ginkgo pollination season rolls around again. 

Real ginkgo forests

Ginkgoes and ginkgophytes (ginkgo like plants) have been around for a long time, 275 million years or so dating back to the Permian.  Presently a single species, Ginkgo biloba, is all that is left, but far from nearing extinction, its ornamental value has redistributed this species around the world.  All of these ginkgo trees are descendants of offspring from some sacred groves of trees protected by monastaries in China, and botanists have speculated for some time about whether ginkgo actually still exists in the wild or whether it persists just as a cultivated plant.  A report in the most recent issue of the American Journal of Botany (August, 2012, v. 99(8): 1408–1414.) has determined that a glacial refugium in the Dalou Mountains harbors natural fragments of ginkgo forest.  The composition of these forests finds that the same plants are still growing with ginkgo as found in the fossil record.  The image is of an 878 year old tree bearing some red feng shui flags for good fortune.  The oldest ginkgo in North America is in Bartram's Garden.  How cool is that?  Maybe next they'll find Glossopteris alive. 

Bartram's Garden - a botanical Mecca

Perhaps it should be Bartrams' Garden (rather than Bartram's Garden because although the garden was started by John Bartram (1699-1777), his son William (1739-1823) inherited not only the garden but his Father's interest in botany and natural history.  Although John Bartram had limited education, Linnaeus, one of the foremost scientists of the day, called him the "greatest natural botanist in the world".  The Bartrams were responsible for collecting and introducing an estimated 150-200 new species to science via specimens sent to Europe collected in the eastern states from upstate New York to Florida and west to the Ohio River.  These included the famous Franklinia alatamaha (named by William to honor Ben Franklin, a friend and associate of his Father).  Franklinia had a very limited distribution and has been extinct in the wild since about 1800, and all the specimens of this beautiful tree alive today are descended from seeds the Bartrams collected and propagated in their garden, North America's first real botanic garden.  Bartram's garden is small, probably occupying no more than 10-12 acres although the property is 3 or 4 times bigger, and it is located just 3 miles from downtown Philadelphia on the bank of the Schuykill River.  This is not a particularly impressive garden in terms of being well kept or having extraordinary diversity (see BGT participants: Mrs. Phactor, Dean of Green & lovely wife Carol,  in the arboretum), but it has a great quality to it.  John's house, built by his own hands, still stands strong, the mark of an excellent stone mason, and a few trees of distinction are still found there.  The oldest Ginkgo in North America grows there, the last of the first three to be introduced to North America from China (via London).  Another notable specimen is a huge (largest in N. America?) yellow wood tree (Cladrastis kentukea) (see image of the tree in flower!) another species collected by the Bartrams.  The Garden is part of the Philadelphia park system now (since 1891) and is surrounded by a rather shabby run-down neighborhood.  But how can you not go and pay homage to this important part of botanical history?  

Ginkgo - coincidence of the day

So the Phactor was deep in concentration this morning working at constructing a photographic plate to illustrate ginkgo leaves and reproductive structures, and the telephone rings. It's a reporter from the student newspaper. "Can I ask you some questions about the smelly tree in front of the music building?" The ginkgo? "Yes, why does it smell?" Perhaps the tree is a non-vocal music critic. Pause. "Oh, ha ha, yes, I get it, but why do the fruits smell so bad?" They aren't fruits; they're seeds with a soft, fleshy outer seed coat. "But they're like fruits." No, they are seeds not fruits. "Everyone calls them fruits." Yes, so why not begin correcting their mistake? The problem is that the tree is not growing in its natural environment, so we really don't know how the smelly seed coat functioned. But think of this. Crap smells and so does carrion, but dung beetles and flies are attracted to these smells, so smelling bad is just a human perspective. "Do you think the smelly mess is a good enough reason to cut the tree down?" No. But wanting to cut down a 110 year old ginkgo tree because it bothers you for 2 weeks is a good argument for a making nature appreciation a required course. "Other ginkgo trees on campus aren't smelly; why is that?" Why don't men get pregnant? Some trees make pollen, some make seeds. "Why did they plant such a tree there?" At the sapling stage when trees can be transplanted is too young for them to be identified as either pollen or seed trees. "What if the cutting the tree was put to a student vote?" Where did you ever get the idea a democratic process would ever be involved in making such a decision? And you should know that the person who actually gets to have and use a chainsaw on this campus loves that tree. "Thank you for all your help, but I've got to get going now." What a coincidence.