As much as I favor native trees, I think it might be hasty to blame the breakup of the Lansing Norway maples on their status as aliens. Anytime we get wet snow before the leaves are out of the trees, there is serious danger of breakup due to overloading of the canopy. I have seen this in native as well as non-native trees. It does seem to occur more often in planted trees than in forest trees. The secret to the problem is latitude of origin, not country. In most years, trees will lose their leaves before the first snowfall, except in those rare years in which a late autumn is combined with an early snowfall. This year does appear to be an unusual one, as I pointed out in my previous discussion about the Shenandoah Valley. The problem is compounded when we move trees more than a few degrees in latitude. In that case, it is very easy to mess up the trees' photoperiod timing. Trees contain an internal clock, called phytochrome, which measures the length of the night. When the night length increases beyond a critical point, which is different for each species, the tree is signaled to prepare for dormancy, including leaf abscission. When we move trees north or south, they can get their photoperiod timing messed up. Forest geneticists have strict rules about the distance over which trees can be moved in tree breeding programs, and have established breeding zones for each species. The horticulture industry has never paid much attention to this, to my knowledge, though it probably enters indirectly into hardiness zone determination. All other things being equal, we would expect, for example, a sugar maple from a particular location to perform better in that location than a tree of the same species from 200 miles N or S. Another argument for local planting stock? It would be interesting to know what the urban foresters on our list have observed over the years about this kind of damage in local vs. non-local trees. This is where being a good naturalist can really pay off over a long period. So, what have y'all observed? Cheers, Tom Kimmerer Forest Biologist University of Kentucky 105 TP Cooper Bldg Lexington KY 40546 Ph (606)257-1824 Fax (606)323-1031 Tkimmer@pop.uky.edu http://quercus.ca.uky.edu
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