Photo: Yu via Creative Commons
Bet You Can Identify a White Birch Tree
By Kevin McKeon, Maine Master Naturalist
Almost everyone knows what a white birch looks like and can easily identify it along trail walks, although differences between white and gray can be challenging. It’s one of five species of birch that live around here: white, yellow, gray, black, and salmon, or river, birch.
The oldest known birch fossils were found in Washington State, dated to 49 million years ago and belonged to the Leopold birch, Betula leopoldae, a close relative of our yellow birch. In Celtic mythology, birch is a tree of beginnings that symbolizes renewal and purification — a link between death and birth. Baby cradles were carved from its wood and then lined with birch boughs for protection and blessings. Mythologically, the black horizontal lines of the white birch’s bark came from thunder bolts thrown by the spirit Thunderbird at the trickster spirit Nanabozho, who took the form of a rabbit to steal fire from Thunderbird at the behest of a tribe’s village elder, Nanabozho’s grandmother, who needed warmth for her people. After a while, Nanabozho took cover from Thunderbird’s lightning bolts under a birch tree. Thunderbird became weary from throwing lightning and left in disgust, creating those black lines from the burning bolts, which we know as .lenticels.
White or paper birch, Betula papyrifera, is extremely well adapted to cold temperatures and winter weather, and around here it’s close to its southern range limit. White birch trees have many adaptations for this cold-loving habitat: white, oily bark that continually sheds its outer, papery layer; large lenticels; sugary sap; and bark that permits photosynthesis. The white bark reflects rather than absorbs heat, helping to keep temperature fluctuations to a minimum, thus mitigating both cracks in tree wood and cambial growth tissue damage otherwise caused by heat expansion cracks from freeze/thaw cycles — common in dark-barked trees. Large lenticels act to increase water and gas intake and let some photosynthesizing light through the bark, allowing the tree to eat a bit during winter. Lenticels are also “one way,” so water and gas enter but can’t escape. That’s why birch bark canoes always have the inner, orange colored bark towards the water; otherwise, water would leak into the canoe from the white side of the bark. Shedding bark keeps dark epiphytical growth (lichen, algae, and moss) to a minimum, maintaining the bark’s heat-reflective whiteness. Also, oily bark acts as a water shield to retain inner moisture, mitigating water loss during winter’s desiccating, cold dry air. White birch also has an adaptation whereby it pumps water out from individual cells to protect cellular damage from freezing, and its sugary sap lowers its freezing temperature.
White birch wood is close-grained and fairly strong, so has found uses as plywood, dowels, toys, clothespins, toothpicks, lathe turnings, and “shoe pegs” — wooden nails used for shoemaking. Those of us who use firewood for our stoves often call birch “biscuit wood,” referring to its high heat output but quick-burning characteristics — perfect for baking biscuits.
Maine’s champion white birch tree, last measured in 2016, was a 31-inch diameter, 85-foot-tall specimen in the Moosehead area. They typically get to be about 2 feet across and live to about 175 years. Many wildlife critters are supported by the birch. It’s a winter mainstay for our moose population, rabbits and deer eat the seedlings and saplings, and a plethora of birds eat the seeds. Yellow-bellied sapsuckers love the sugary sap, and the holes these birds make also attract insects and feed highly territorial hummingbirds — who work with the sapsuckers to defend this food source.
Lenticels: https://sanfordspringvalenews.com/out-in-the-woods-60/
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net
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