Dawn redwood: A living fossil

Dawn redwood: A living fossil

In 1940, scientists found some fossils in Japan for a new, unfamiliar species of wood that was quite similar to redwood and sequoia that are living trees in California. (Since this find, fossils of the same genus have been found in the Badlands of western North Dakota.) Then in China in 1941, botanists and foresters were surprised when three living trees of an unknown species, that eventually turned out to be the same tree as the fossils, were found in southeast China. These three trees were named dawn redwood. Over the next decade, more living trees of this species were found in this same region of China. Seeds of these trees were collected and were been planted in various locations throughout the world. Now, as these trees mature and more are being planted, the wood properties are being collected and published. Lumber is showing up in the marketplace.

Dawn redwood is a very fast growing softwood tree, if grown in good conditions with lots of water. Many trees are more than 100 feet tall and more than 3 feet in diameter at age 26 years. This growth rate is very attractive to foresters and land-owners. It has the potential to be a short-rotation crop tree.

The wood is somewhat similar to California redwood: it is soft with pinkish heartwood and white sapwood, is fairly weak, and has excellent resistance to decay fungi. Although the wood is probably too soft for decking material, it could be used for house siding and shakes, boat houses, outdoor furniture, garden trellises, outdoor signs and carvings, and similar items not requiring strong wood.

Processing suggestions and characteristics

Density. The density of samples collected has ranged from 18 to 26 pounds per cubic foot. The lower densities are for the faster growing material and the higher density for slower growth. (For comparison: California redwood old-growth has a density of 28 pounds per cubic foot; second growth is about 24 pounds per cubic foot. Eastern red cedar is about 33 pounds per cubic foot.)

A 1 x 6 x 6 foot piece of lumber, dried and planed, will weigh only 3-3/4 pounds. (For comparison: California redwood old-growth would weigh 4-3/4 pounds; second growth, 4 pounds; eastern red-cedar, 5-1/2 pounds.)

Drying. Drying is very easy. The wood should be dried using the same procedures as California redwood, which includes end coating green lumber. It is not known if collapse will be a problem; if it is, then steaming at the end of drying to recover collapse will be necessary.

Shrinkage has been measured as 1 percent radially (width of a quartersawn piece of lumber) and 7 percent tangentially (width of a flatsawn piece of lumber). The radial shrinkage is exceptionally low, but the tangential shrinkage is quite high for a low density wood. (Possibly some collapse occurred in the tangential samples accounting for the large number.) California redwood has about 2 percent radial and 5 percent tangential shrinkage.

Gluing and Machining. Gluing is easy.

Machining requires exceptionally sharp cutters to avoid compressing the fibers and subsequent fuzzing. Rake or hook angles must be increase, compared to oak, by 10 degrees or so. Sandpaper must be sharp (i.e., fairly fresh) and only low pressure applied when machining or sanding to avoid compression and subsequent “springback”of the compressed areas when the relative humidity increases.

Stability. Except for the excessive swelling of collapsed wood the first time such wood is exposed to high RH, dawn redwood is fairly stable tangentially (4 percent MC change for a 1 percent size change) and exceptionally stable radially (15 percent MC change for a 1/2 percent size change).

Strength. The strength (MOR) of low density dawn redwood was 6400 psi; high density was 8000 psi. The stiffness (MOE) of low density was 0.48 million psi; high density was 1.1 million psi. The hardness ranged from 310 to 370 pounds. (For comparison, second growth California redwood values are 7900 psi, 1.10 million psi, and 420 pounds.)

Color and Grain. Dawn redwood has heartwood that is more pink than red. The sapwood, which can be several inches wide around the outside of the heartwood, is brilliant white. The annual rings are not real obvious. Due to the fast growth, the grain is considered coarse.

Dawn redwood branches, when they die, do not decay or fall off easily, so the wood grows around these dead branches. As a result, the knots found will often have in-grown bark, similar to what is called a black knot in pine. Such knots may loosen drying manufacturing.

This post appeared first on http://www.woodworkingnetwork.com

Leave a Reply

Your email address will not be published.

This website nor its owners are an actual service provider, this website is a referral service. When you place a phone call from this website, it will route you to a licensed, professional service provider that serves your area. For more information refer to our terms of service.

© WoodFloorRefinishing.info

(877) 959-3534