We have had a wonderful display of fall leaves this year. Fall leaf colour is the result of leaf senescence, the process by which trees recover valuable mineral nutrients such as phosphorus and nitrogen from leaves before winter. Leaves change colour when chlorophyll synthesis stops and the current chlorophyll degrades, revealing the yellow carotenoids in the leaves. Anthocyanins, which are produced in some leaves as the chlorophyll breaks down, give red and purplish tints. Dry, sunny days and cool nights promote the formation of anthocyanins.
The forest is beginning to open up as the leaves drop from the trees and the undergrowth dies back. The dense green forest of just a month ago has been replaced by the bare branches of trees and a carpet of colored leaves underfoot.
Not all the trees in the forest are bare. Some tree species hang on to their leaves a bit longer than others, and the copper leaves that now stand out in the forest make the American Beech (Fagus grandifolia) trees easy to find. Some beech leaves will persist through the winter. The dead leaves that are retained are termed marcescent, and are most common on beeches and oaks. For more on marcescent leaves, see Dressed for Winter
The leaves of some of the smaller beech trees were yellow, rather than copper. It is usually the youngest trees that retain dead leaves, so perhaps this difference in marcescence is reflected in the different leaf colours. Thanks to Birdgirl for this suggestion!
Beeches are trees of the climax forest, often found growing with larger trees like sugar maple, red oak, white ash and white pine, where they thrive in the shade of their bigger cousins. They are slow growers, but can live to be 200 to 300 years old. Beech trees often re-propagate by producing a colony of clones that sucker from the roots of the adult tree.
Like other species such as the White Elms (Ulmus americana), which were decimated by Dutch Elm Disease as the result of a fungus imported from Europe, and the American Chestnut (Castanea dentata), nearly wiped out by an imported Asian bark fungus (Cryphonectria parasitica), beech trees have also been attacked by a foreign invader. The beech scale (Cryptococcus fagisuga), a tiny insect with formidable piercing and sucking mouth mechanisms, arrived in America with an imported European Beech and, along with a companion fungus, has laid waste to beeches across eastern North America.
Beeches have beautiful, smooth grey bark. They make an inviting surface for initial-carvers, but the wound inflicted by this destructive practice can provide an entry point for disease. Below, the bark of this Shagbark Hickory (Carya ovata), growing close to the beech tree in the opening photograph, provides an interesting contrast to the smooth beech bark.