In 2003 the Northeast United States suffered a power outage that was the second most widespread electrical power outage in US history. More than 10 million people in Canada and 45 million people in the United States were affected. The blackout was caused when high-voltage power lines came in contact with "overgrown trees". The cascading effect that resulted forced the shutdown of more than 100 power plants. It took nine seconds for the grid to collapse.
In January 2009 a major ice storm produced widespread power outages for more than 2 million people in the Midwest. Ice-laden trees and branches contributed to outages as they crashed down onto power lines throughout the eight state areas impacted.
These are but two examples of why vegetation management is important. The maintenance of power line right-of-ways for both transmission and distribution lines are essential to assuring system reliability.