Friday, February 15, 2008
Biodiversity Corner - Butternut, or identifying trees in winter
Since the fall I have been wondering about a broken tree at the edge of the Towle Field. The tree is wrapped around with oriental bittersweet, an invasive and destructive vine which almost certainly contributed to the tree's demise.
Last Saturday, February 9, Concord- Carlisle Community Education ran a "Botanical Tour of the Towle Land" led by Michele Grzenda, who showed us how to identify trees and shrubs in winter. By the time we came to the broken tree, about an hour into the tour, she had already taught us many of the signs you can use to identify trees without leaves. She then took us through the questions from her dichotomous key, and together we identified the tree as a butternut.
Name. Butternut is also known as white walnut and sometimes as oilnut. The scientific name is Juglans cinerea. The genus name Juglans comes from the Latin words Jovis meaning Jupiter and
Clues for twig detectives. A large part of identifying trees in winter is knowing what to look for. In addition to obvious things like silhouette, growth pattern, bark and habitat, a lot of the visual indicators involve twigs and in particular the buds — their position, size, color, shape, scales and fuzziness. My favorite visual sign is the shape of the leaf scar, the mark left on the twig when the leaf falls off. Visual signs can also include secondary indicators like evidence of caterpillars (e.g., tent caterpillar remains on the black cherry) and species-specific fungi (e.g., cedar-apple rust on the eastern red cedar). But the clues are not all visual. You can use more than look-and-see — we got into scratch-and-sniff, chew-and-taste, and touch-and-feel.
Distinguishing characteristics. The combination of characteristics that distinguish the butternut are alternate buds, a terminal bud which is longer than it is broad, cross-partitions in
Similarly, the chambered pith is a feature of both black walnut and butternut but only the butternut has dark brown pith. It was possible to identify this tree from just four or five inches of a leafless twig.
Sources. Concord-Carlisle Community Education instructor Michele Grzenda, conservation agent for the Town of Framingham; Winter Tree Finder, May T. Watts and Tom Watts (this book had the key we used in the field for the butternut); Trees of the Eastern and Central United States and Canada, William M. Harlow; Virginia Tech College of Natural Resources at www.cnr.vt.edu (search for "twig key"); Tree Identification Book, George W. D. Symonds.
© 2008 The Carlisle Mosquito