Why does cold weather cause tree branches to fall?

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Heavy loads of ice and snow cause branches and sometimes entire trees to fall. This is particularly true for trees with upright branches or other structural weaknesses, such as rotten limbs or cracks. Vicious winter windstorms also fell weakened branches, but careful winter pruning is one method for minimizing injury to trees. It also helps avoid damage and accidents caused by branches falling on people, cars and roofs.

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1. Snow, Ice and Windstorms

   • The Gaithersburg, Maryland, emergency call center received calls about 742 fallen trees and 285 broken tree limbs, all after one powerful winter storm in February 2011. The Gazette.net news website noted that the combination of snow, freezing rain and wind created stresses that many trees could not withstand.

     The Morton Arboretum of Lisle, Illinois, notes that it is important to remove snow gently before it freezes to limbs and branches. It warns that trying to remove ice from trees can cause further damage and recommends waiting for it to melt.

   Dangers of Damage

   • Aside from harming the growth and survival of trees, heavy snow and ice loads on tree limbs can be dangerous. In New York's Central Park, a tree limb weighted down with snow fell and killed a 46-year-old man in 2010. "The New York Times" article about the accident said that another man suffered serious injuries in the park the previous summer when struck by a falling, rotten branch. Structural damage, such as rot or cracks, can create accidents at any time of year.

   Structural Problems

   • Structural flaws aren't all caused by winter injury or old age. The Chicago Trees Initiative website says that branches of trees with upright growth structures, such as flowering pears (Pyrus calleryana), form weak unions with their tree trunks due to their upward sweep. The angles at which they join the trunk are usually less than 45 degrees. One example is the Bradford pear, which has become infamous for splitting along its trunk during winter storms.

   Winter Pruning

   • Winter is a good time to thin and prune trees in preparation for spring growth. It is also the time when tree sap slows down. The Chicago Trees Initiative website says to remove dead, diseased and damaged branches first. Also remove branches that are crossing or rubbing each other. Thinning the density of a tree's branches improves air circulation and wind resistance while also decreasing the surface area available for snow accumulation. It is important to do the work on dry, sunny days that aren't windy. When removing heavy branches, tie them to the limbs above before cutting, then lower them slowly to the ground to avoid accidents.

Source: www.ehow.com

Tags: tree branches, branches fall, cause tree, cause tree branches, Chicago Trees