The Puget Sound lowland forests were once dominated by dense coniferous forests made up of western red cedar, western hemlock (Tsuga heterophylla), and Douglas-fir (Pseudotsuga menziesii). These forests represented both a valuable resource and an obstacle to agriculture. Therefore, their removal began early, and now there are very few old growth sized trees in our cities.

The Douglas-fir is not a fir; its scientific name means Pseudotsuga or "False Hemlock." The Douglas-fir is named after the Scottish botanist, David Douglas, who introduced many Northwest native conifers to Europe. The tree's scientific name, Pseudotsuga menziesii, honors Archibald Menzies. Menzies was appointed as naturalist to accompany Captain George Vancouver on his voyage around the world on HMS Discovery.

The Douglas-fir, state tree of Oregon as seen on their license plates, is the second tallest tree species in the world. In August, Oregon State University researchers published their findings about the limits of growth in trees like the Douglas-fir. Douglas-firs finally stop growing taller because they can't pull water any higher. This limit on height is somewhere above 350 feet, or taller than a 35-story building. Here is more information from their web site: http://oregonstate.edu/dept/ncs/newsarch/2008/Aug08/douglasfir.html

"People have always been fascinated by how some trees, such as Douglas-fir or redwoods, can grow so tall," said Barb Lachenbruch, a professor of wood science at Oregon State University. "This is not an easy thing to do. Think about trying to drink water through a narrow, 350-foot-long straw. It takes a lot of suction."

Douglas-fir wood consists mostly of dead cells called "tracheids" that function in water transport and physical support. These tracheids have pits on their sides that function as valves, allowing water to go from one tracheid to the next, and the pits have a membrane with an impermeable middle. Normally, water flows through the porous edges of the membrane, but if there's an air bubble in one tracheid, the membrane moves to the side and blocks off the pit so air bubbles can't spread. Because water is pulled through a tree by the forces of evaporation from the leaf surfaces, the water is in "tension," like a pulled rubber band. If an air bubble gets in, it's like the rubber band breaking and water can no longer be transported.

"Higher and higher in the tree, the valves change so they are able to withstand more pulling force from the long, heavy column of water before air bubbles can be sucked through," Lachenbruch said. "But the problem is that the valves become less efficient at letting water pass. The height at which no water would pass at all, according to our models, coincides with the tallest records for Douglas-fir, about 350 to 400 feet."