I've been following the recent postings with great interest, and I apologize for not having time to say anything about fall colors from a physiologic standpoint. Too busy with teaching and new baby. I just had the pleasure of driving from Kentucky to Washington D.C. via the Shenandoah Valley, and back via Western Maryland. So I got a real eyeful of fall colors. I noticed some striking differences between this year and several previous years. Fall is much patchier this year. In Western Maryland and West Virginia, you could see yellow-poplars in full glory in one hollow, entirely green in another, and brown in another. Same with oaks and hickories. I suspect that the reasons are: 1) we are having a very long fall with no sharp temperature drops; 2) many areas in the east had serious droughts in July and/or August. 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. The drought effects are more complex, but basically trees that go into autumn in poor physiologic condition will have poor colors. The most intense colors are in years when a good growing season is followed by a dry autumn. In many areas of the Eastern Deciduous Forest (EDF), the dry period came early this year. Lexington's urban forest got hammered in late July, with many trees wilting and some trees with abnormal late-season shoot growth. The irregular distribution of drought in mid-summer may explain the patchiness of fall coloration. All in all, this has been a particularly glorious prolonged autumn throughout the EDF. And all you New Englanders can keep your gaudy colors - here in the heart of the EDF, with the highest temperate species diversity in the world, we have the subtlety and richness of colors that result from our amazing mix of species. Two last observations: 1) one can't help but notice the great beauty of hickories in the fall, and wish they could have more of a place in the landscape; and 2) there are an amazing number of non-native trees in the Shenandoah valley, and on the edges of Shenandoah National Park. Ailantus altissima is especially abundant. Cheers, Tom Kimmerer Forest Biologist University of Kentucky Lexington KY 40546 Visit the TreeWeb: http://quercus.uky.edu tkimmer@pop.uky.edu
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