Forest Products

Commercial Species

Alaska (Yellow) Cedar (Chamaecyparis nootkatensis) & Western Red Cedar (Thuja plicata)

Written By: Eugene E. Wheeler, Retired USDA Forest Service Program Manager for Cooperative Forestry Programs, (Alaska) Region 10. Currently a consultant for Idaho Panhandle Forestry.

Introduction

This booklet contains a brief discussion of the botanical and wood structural characteristics, forest associations, and some of the commercial uses of Alaska yellow cedar and western Red Cedar in Alaska.

Both species are coastal species and have decay resistant. However, their characteristics diverge from there. These differences, as well as similarities, will be pointed out. This booklet is nontechnical and provides an introduction to the two species, and the Alaska forest environment in which they grow.

The Climate

The habitat of the two cedars in Alaska is an extension of the rain belt forests of Oregon and Washington. This rain belt extends along the Alaska coast to Kodiak Island. The forest environment of coastal Alaska is wet to extremely wet with moderate temperatures. Precipitation ranges from 60 to over 200 inches (152 to 508 centimeters) annually. Summer temperatures are from 47°-70°F (7°-21°C), while winter temperatures can drop below -20°F (-29°C). The growing season is moderately short (130-160 frost free days), with long periods of daylight (18-21 hours) which provide optimum solar energy for maximum tree growth.

Both cedars are slow growing and are found most often on the poorer soils. Best growth in natural stands is found on very wet sites in the fog belt along the coastal plain. This is probably because the Sitka spruce or hemlock cannot compete with the cedars on these sites.

The Forest

The coastal forests of Alaska occur from shoreline to elevations of 2,000 to 3,000 (610 to 914 meters) and from the southern end of Alaska to Kodiak Island. Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) dominate the forests of coastal Alaska, especially on the deeper, well-drained sites of the river flood plains and lower slopes. Mountain hemlock (Tsuga mertensiana) dominates the upper slopes, extending to elevations above all other species (up to 3,500 feet or 1,067 meters). The two cedars are found in association with Sitka spruce and western hemlock on the lower slopes and flood plains and with mountain hemlock on the upper slopes. Western red cedar attains its best growth below elevations of 500 feet (152 meters), while Alaska cedar reaches its best development between 500 and 1,200 feet (152 and 366 meters). Western red cedar is not found beyond Fredrick Sound, whereas, Alaska cedar extends as far westward as Prince William Sound. The two cedars seldom occur as pure stands, except on very wet soils where competing species cannot survive. There are about 13.25 million acres of forest land in coastal Alaska, including all of the islands which make up a significant portion of the acreage. Sitka spruce and western hemlock types account for 96% of the forest area. The balance is comprised mostly of mountain hemlock and an insignificant acreage of cedar types.

Wood Properties

Because there are many differences in wood properties, the two species will be discussed separately.

Western red cedar wood has a distinctive odor characteristic of cedars. Summerwood is distinctly narrower, darker, and harder than springwood. The wood has a fine, moderately even texture. It is light in weight, weak in bending, moderately limber and soft, low in shock resistance, and has a very small shrinkage when seasoned. The wood is straight grained. Red cedar is moderately easy to kiln dry, stays in place well, very easy to work, moderately easy to glue, and takes paint and stains satisfactorily. The wood is resistant to termite attack. Red cedar wood works easily resulting in a good finish but is somewhat brittle and may splinter. Chip bruises may occur unless the waste disposal system keeps the working surfaces clean. The soft springwood may be depressed by dull tools only to rise later creating ridges on the surface.

Alaska yellow cedar heartwood is a bright clear yellow, while the sapwood is lighter in color. The wood contains a volatile oil which gives it a distinctive odor and may add a gloss to worked surfaces. It has a fine, even texture and is relatively straight-grained. The wood is heavy in weight for a softwood, moderately weak in bending and compression, moderately stiff, moderately hard, moderately high in shock resistance, and has a small shrinkage when seasoned. Alaska cedar is very easy to kiln dry, stays in place well, is very easy to work, but has a low nail-holding capacity. It is easy to glue, may not take paint or stain well if not properly dried, and works very easily without the problem of brittleness or soft grain that red cedar has. The wood has unusually high static and impact bending strength for a softwood species.

Seasoning

The cedars air dry slowly in the coastal area and if air dried, the best site and quality control must be used. Both species are easily kiln dried. However, lumber sawn from wet red cedar logs such as "sinkers" must be air dried to a 50% or less moisture content prior to kiln drying. Otherwise, the wood cells may collapse and honeycomb. Drying schedules for red cedar vary from 50 hours to 22 days at temperatures of 120°-140°F (49°-60°C) with wet-bulb depressions of 5°-10°F (3°-6°C).

Drying schedules for Alaska cedar vary from 72 hours to 7 days at temperatures of 130°-160°F (54°-71°C) with wet-bulb depressions of 2°7°F (1°-4°C).

Other Properties

The following wood properties are averages derived from previous U.S.F.S. reports concerning the two cedar species. The figures are averages derived from tests on samples of woods harvested in Alaska. Variables from other known data may be caused by growing and handling conditions.

I. Weights

A. Solid Wood - Average weight in pounds per cubic foot (kilograms per cubic meter).

Alaska Cedar

B. Logs (Approximated)

1. Average weight per log in pounds. (Kilograms)

Western Red Cedar

Alaska Cedar

2. Average log weight per MBF using Scribner Decimal "C" Log Rule Scale.

C. Lumber - Average weight in pounds (kilograms) per MBF.

II. Specific Gravity

III. Shrinkage - Percent from green to seasoned, based on original green dimensions.

* Flat-grain board. Reverse for quarter-sawn or edge grain board.

IV. Basic Strength Values and Mechanical Properties of Red Cedar and Alaska Cedar.

(Strength properties of white spruce increase as the wood is dried out.)

A. Hardness - Load required to embed a 0.444 inch (1.1 cm.) ball to 1/2 its diameter.

B. Static Bending

Modulus of Rupture

Modulus of Elasticity

Work to Elastic Limit

Work to Maximum Load

C. Impact Bending - Height of drop causing complete failure - 50 lb. (22.7 kg.) hammer.

D. Compression Parallel to the Grain Fiber

E. Shearing Strength

F. Tension

G. Compression (Perpendicular to grain, fiber stress at elastic limit)

* Pounds per square inch - psi
** Kilograms per square centimeter - ksc

Uses of the Trees

Both Alaska cedar and western red cedar are being exported to Japan as round logs. An exception to the U.S.F.S. primary manufacture rule has been granted to timber purchasers of national forest timber, making the cedars a prime export product.

The two cedars are highly valued for boat construction when wood is the chosen construction material. Both cedars are highly durable and resist attack by the various insects which are encountered in the marine environment. The cedars are used extensively for poles, piling, light construction, fence posts, lining for boxes and closets, and as stock for specialty products such as toys. Red cedar is the most widely used wood for shingles and shakes. Alaska cedar is highly valued for window frames, doors and other fine finish purposes for which wood is the most desirable material.