January 17, 2010
Photographer: Dale L. Hugo
Summary Author: Dale L. Hugo; Jim Foster
Robert Frost wrote of birches being bent by either boys swinging on them or by ice storms. An ice storm along Minnesota's North Shore of Lake Superior in late March 2009 coated birch trees, and everything else, with up to two inches (five centimeters) of ice! An accumulation of a quarter inch (half a centimeter) or more can cause severe damage. Because tree limbs were completely glazed over, the weight of all the ice bent the more supple trees but snapped the more brittle species. Due to their high surface-to-volume ratio, trees are more susceptible to damage during ice storms than during many other severe weather events. Frost observed of ice covered birches:
"…they seem not to break; though once they are bowed/So low for long, they never right themselves...."
The fate of the bent birches, and the ramrod straight one as well, is to eventually die off as a result of forest succession. Many stands of dead birches now show their pale white trunks and leafless branches along the Lake Superior shoreline. Their lifespan is from about 60 to 80 years. These birches are first and second growth trees. Fires and aggressive logging a century ago removed the old-growth forests down to bedrock. As the birches die off, pine and spruce will again predominate along the North Shore.
Minnesota's North Shore of Lake Superior coordinates: 47.310367, -91.207983
Earth Observatory images: