Trees can tell us quite a lot about the past. Just ask Dr. Paul Knapp.
For the past two summers, Knapp, professor of geography, spent time in Oregon reconstructing windstorm history by examining our silent companions in time trees.
Windfall along a trail at Cascade Head, Oregon, caused by a December 2007 windstorm that generated 125+ mph winds along the Oregon Coast.
He and Portland State geography professor Dr. Keith Hadley have been examining old-growth trees in several state parks and Research Natural Areas along the Pacific Northwest coast. They start by looking for trees with missing tops proof they stood through some powerful storms.
These storms can be huge and generate wind speeds over 150 mph, Knapp says. It's the West Coast equivalent of a hurricane.
With an increment borer they take samples from the trees and look for growth patterns. With the information provided by the annual ring widths exceptionally narrow or wide rings indicating windsnap and windfall, respectively they can infer the strength and date of the storm. And because they are working with old-growth trees, they can determine wind events as early as the 16th century.
We see decent-sized storms every 3 to 5 years and major storms every 10 to 15 years, he says. So far the tree-ring data match with the historical records.
The question at the heart of the research is to place windstorm event activity of the 20th century in a larger historical context by comparing it to windstorm frequency during the previous three centuries.
Windstorm activity in the Pacific Northwest is well documented only from the 1950s onward, so we donít know how representative this period is to previous centuries where there may have been significantly more or less activity, Knapp says.
Analysis is expected to be completed by spring 2011.