Blowdown

Overview

• Severe weather events can cause pockets or large areas of forest to blowdown, which can result in some or all trees within an area to break off or uproot.
• Blowdown events in Ontario usually range from 5 to 50 hectares in size, but can get as large as 500,000 hectares, particularly in the boreal forests of northern Ontario.
• Other terms used include: windthrow, windblow and stem breakage.

Damage characteristics

• Some blowdown events level most or all of the trees in a stand, with the trees lying in the same direction on the ground.
• This is common in spruce and jack pine stands in the boreal forest.
• In poplar or mixed-wood stands, often only tops or portions of trees are damaged, breaking off near the crown.
• Areas of blowdown become a fire hazard as the dead trees dry out.
• Blowdown is often caused by a straight-lined wind storm that is referred to as a “derecho”.
• The 2005 blowdown near Lac Seul in northwest Ontario was over half a million hectares in size.