This article, which appeared in the February 2009 issue of Sawmill & Woodlot Magazine, is part of S&W Publishing LLC’s “Tree Species” series and is not intended for reprint or republication. It is posted here with permission from Sawmill & Woodlot Magazine. To access copies of Sawmill & Woodlot’s “Tree Species” articles, visit http://sawmillmag.com/treespecies.php
AN EVERGREEN SPECIES, redwood (Sequoia sempervirens) is immediately recognizable due to its size (enormous) and color (very red). In North America, redwood grows primarily in California. Although much of the redwood forests have been harvested or are now reserved, there are still good supplies, albeit expensive, of redwood logs available from replanted forests. The wood itself is lightweight and even grained. For many years, low shrinkage and natural decay and insect resistance made it a popular wood for house siding and decks, as well as for water towers for railroad steam engines. There are over 30 lumber grades for redwood lumber. As a rule of thumb, when the lumber is all heartwood, the grade name will contain the wood “heart.” Major grade divisions include architectural (top clearness), garden, heart, and sap. Many products are made today using both freshly harvested redwood and old timers. Redwood is so valuable and durable that recycling is socially responsible and makes economic sense as well. Some old-growth redwood logs are available from forests where the trees have been blown down and have been sitting on the ground for 50 years or more. Redwood veneer products are also popular, as only a little redwood is used in the plywood product, with the core veneers being a more available, less expensive species.
PROCESSING: Suggestions and Characteristics
DENSITY. Redwood weighs about 23 lbs. per cubic foot. Most other softwood species are somewhat heavier. The lumber weighs about 1-1/2 pounds per board foot, kiln-dried and surfaced.
SAWING. This wood is so valuable that careful sawing is the only way to go. Thin-kerf saws are essential. Flatsawing is best. Know what thicknesses your customers want before beginning to saw. Careful attention to heartwood and sapwood is required due to the premium for all heart pieces. To minimize the number of pieces with sapwood, always saw parallel to the bark. Short pieces of redwood also have good value. Avoid heavy slabs. (Note: For recycled wood, tramp metal is an issue. Scanning is essential. Avoid using expensive blades that can be damaged.)
DRYING. Drying requires care to avoid severe end splits and collapse. Slow careful drying is the rule, with end coating essential. With older growth, water pockets and areas of collapse are common. Steaming after drying to recover collapse is required when collapse occurs. Shrinkage from green to 10% MC is only about 3%; most other species would be over 5% shrinkage. Final moisture contents can be 10% to 12% MC.
GLUING & MACHINING. Redwood glues very easily. The open structure requires a little more adhesive than with heavier woods. Avoid excessive pressure. Machining is excellent if the tools are sharp. Dull tools tend to push over or mash the fibers, not cutting them cleanly. Sharp sandpaper is also important using light pressure.
STABILITY. The low shrinkage means that the wood is very stable when the MC changes in-use. This property means low warp in-use. It also means that when painted, there will be little stress on the paint film, so the paint will adhere and last for years even when there is a lot of wetting and drying of the wood.
STRENGTH. Redwood is fairly weak, as might be expected from its low density. Its strength (MOR) is approximately 7,900 psi, which is a little weaker than eastern white pine (8,600 psi). Its stiffness (MOE) is 1.1 million psi. Hardness is 420 lbs.
COLOR & GRAIN. Redwood is almost all heartwood, which is very red in color. The outer rings of the tree are white sapwood, but little of this is included in lumber. The grain of redwood varies somewhat from tree to tree. Typically, the wood is soft and fine grained, but sometimes the grain is very coarse (or open). The grain is straight and not as distinctive as with most pines, for example.
TREE CHARACTERISTICS It is not unusual for a redwood tree to reach 300 ft. in height and 12 ft. in diameter at maturity. Giant sequoia is even larger and is a different species. Second-growth redwoods, available from replanted forests, are plentiful both in California and in New Zealand. In fact, New Zealand’s redwood trees grow so rapidly that within 50 years they are gigantic and ready for harvest. Interestingly, for such a large tree, the cones are scarcely 1 inch in length.
PESTS & DISEASES Redwood’s resistance to fungal pathogens and injurious insects is seemingly unparalleled among tree species in North America. Most of its insect pests nibble at foliage, buds, or cones, and feeding by redwood bark beetles is largely confined to dying branches and severely weakened trees. Redwood’s most common disease is heart rot, caused by a white ring rot in the northern part of the tree’s range, and a brown cubical rot elsewhere. Both fungi gain entry to the bole through fire scars at the base, which as a result is often hollow in older trees. These hollows are known locally as “goose pens,” owing to their frequent use as poultry shelters by early settlers. Redwood canker, apparently caused by any of three different fungi, can form on branches and, less often, on tree stems, but it rarely girdles the tree, and it tends to result in more damage to hosts planted outside of their native range. Perhaps the most serious concern regarding redwood is its potential vulnerability to Phytopthora ramorum, the pathogen responsible for sudden oak death, which has killed a staggering number of oaks and tanoaks along the U.S. West Coast (from southern California to southwest Oregon). Phytopthora ramorum (first observed in the U.S. in 1995) is not native to North America, although its origin is uncertain. It seems to thrive only in cool, moist environments, and thus is currently confined to coastal habitats like those occupied by redwood. Redwood, along with dozens of other North American plant species, can be infected by the pathogen, but the long-term implications of infection for our featured species are as yet unclear.
MARKETS. If softness is not an issue, then redwood is an excellent material for decks (although treated southern pine is used more often), outdoor furniture (although western red cedar and some imported species are now used more often), and house siding (although western red cedar and non-wood products are used now). Redwood is exquisite for interior paneling and flooring. It is also popular for novelties. Unless a mill is a member of the California Redwood Association, marketing graded lumber will be difficult. Personal contacts and visits to potential customers will likely produce the best results for the smaller mill. This also means that the mill will have to offer drying and some remanufacturing options. Redwood shingles and shakes are also a possibility.
Gene Wenger is a Professor Emeritus at the University of Wisconsin-Madison and president of The Wood Doctor’s Rx. He can be reached at [email protected].
Eric Kruger is a professor in the Department of Forest Ecology & Management at the University of Wisconsin-Madison. He can be reached at [email protected].