Bud, Twig, Branch, Trunk
Damage, symptoms and biology
Glaze ice is a smooth, compact deposit of ice, generally transparent, formed by the freezing of supercooled drizzle droplets or rain droplets on objects with a surface temperature of 0°C or lower. It forms a sheet on all sections of objects that are exposed to precipitation. The ice build-up can increase the weight of tree branches up to 30 fold. The accumulation of snow or glaze ice in the crown causes compression stress on the stem and may cause part of the tree to bend over if the stem is not perfectly straight. Branch breakage depends on a number of factors, such as the tree species, wood density, presence of knots and the tree's architecture. In addition, glaze ice causes the loss of a large quantity of twigs and buds which results in slowed growth the following spring. Specialists have established a vulnerability classification system for trees, but the ranking may vary with the location, the immediate environment and the age and health of the tree. Some of the most vulnerable tree species include the American elm, silver maple, black cherry and basswood. Sugar maple, red maple, white ash, red oak and white pine are intermediate in terms of vulnerability, while eastern hemlock, white spruce and hickory are among the most resistant trees.
The 1998 ice storm caused the death of 22 people in Quebec. About a thousand electrical transmission towers were toppled along with 24 000 hydro poles, and 120 transmission lines were damaged. The storm required the mobilization of 12 000 soldiers, marking the largest peacetime military deployment in Canada's history. Three million people lacked power simultaneously at one point during the storm and tens of thousands had no electricity for more than a month. In all, 454 temporary shelters were established, serving hundreds of thousands of people affected by the storm. In Eastern Canada, 35 000 km2 of forests were affected by the ice storm, with moderate to serious damage reported in 15 200 km2 of this total, of which 11 700 km2 were in Quebec.
Canadian Forest Service Publications
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