Courtesy Twin Cities NaturalistCheck out this week's Phenology Roundup where professional naturalist Kirk Mona of Twin Cities Naturalist discusses what's been seen around the Twin Cities area in the last week. Phenology is the science of the seasons. It looks at how and when nature changes according to seasonal climatic conditions.
If the leaves ever actually fall from the trees this autumn, it will be the last fall for us to use standard garbage bags to bundle them up here in the Twin Cities metro area. We're going green with yard wastes starting with in the spring due to a new state law. Read all about it here.
Oh, sure. Autumn looks pretty, with its big flashy colors and brilliant blue skies. But that’s just a mask it wears to disguise its true, evil intentions. Everything good in the world is dying, all around us, and there’s nothing we can do about it. In fall the nights grow longer, the days colder. Beaches close. Bicycles get packed away for the season. The two most perfect inventions of the mind of man – daylight saving time and baseball – both come to a close. It is the end of life as we have known it. And all we have to look forward to are endless months of icicle winds, lowering skies, and – worst of all – football.
The fiery colors of Autumn are the flames of a funeral pyre, a sign of death and decay. According to Susan Carpenter, native plant gardener at the University of Wisconsin-Madison Arboretum, leaves depend on the chemical auxin to keep open the tubes that supply water, sugar and nutrients. But the cooler temperatures and shorter days of Autumn shut off auxin production. The tubes are cut off, and the leaf strangles and dies. Chlorophyll, the green chemical that gives leaves their summer color, disintegrates, leaving behind two other chemicals: yellow carotene and red anthocyanin. Different tree species contain these chemicals in different amounts, resulting in the various colors we see.
Trees are at their most colorful when a cool, wet summer is followed by a sunny, dry fall. Rainfall promotes tree growth, and moderate temperatures prevent scorching in the summer sun. Extra sunlight in the fall allows trees to continue producing their chemicals right up to the end.
Here in Michigan, we had pretty much the opposite – a summer of drought and searing temperatures, followed by a fairly wet fall. The trees have been pretty brown since mid-September, though a few of them are making a late run at color. Don’t bother, boys. We’re depressed enough as it is.