Tsuga heterophylla

 

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Family: Pinaceae

 

 

 

 

 

 

 

 

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Western Hemlock

 

 

 

The genus Tsuga contains about 14 species native to North America [4] and southern and eastern Asia [10]. The word tsuga is the Japanese name for the native hemlocks of Japan. The word heterophylla means ‘with other (different or various) leaves’.

Other Common Names: Alpine hemlock, alpine spruce, berg-hemlock, black hemlock, mountain hemlock, Olympic fir, Pacific Coast hemlock, Patton's hemlock, Patton's spruce, Prince Albert's fir, tsuga de California, tsuga de Californie, tsuga de l'ouest, tsuga de Patton, tsuga di California, vastamerikansk berg-hemlock, weeping spruce, westamerikanische hemlocktanne, western hemlock, western hemlock spruce, Williamson's spruce.

Distribution: Western hemlock is native to the Pacific Coast region from southern Alaska (Kenai Peninsula) southeast through southeastern Alaska and western British Columbia to western Washington, western Oregon and northwestern California. Also in the Rocky Mountain region from southeastern British Columbia south to northeastern Washington, northern Idaho and northwestern Montana.

The Tree: Western hemlock trees reach height of 200 feet, with diameters of 3 feet. An exceptional specimen was recorded at 259 feet tall, with a diameter of 108 inches.

General Wood Characteristics: The heartwood and sapwood of western hemlock are almost white with a purplish tinge. The sapwood, which is sometimes lighter in color, is generally not more than 1 inch thick. The wood often contains small, sound, black knots that are usually tight and stay in place. Dark streaks are often found in the lumber; these are caused by hemlock bark maggots and generally do not reduce strength. Western hemlock is moderately light in weight and moderate in strength. It is moderate in its hardness, stiffness, and shock resistance. It has moderately large shrinkage, about the same as Douglas-fir. Green hemlock lumber contains considerably more water than Douglas-fir, and requires longer kiln drying time. Trees may contain wetwood and/or have ring shake. The wood is intermediate in nail holding ability and has a tendency to split when nailed. It is satisfactory with respect to being glued and in taking stains, polish, varnish and paint.

 

 

Mechanical Properties (2-inch standard)

 

 

 

 

Compression

 

 

 

 

Specific

gravity

MOE

x106 lbf/in2

MOR

lbf/in2

Parallel

lbf/in2

Perpendicular

lbf/in2

WMLa

in-lbf/in3

Hardness

lbf

Shear

lbf/in2

Green

0.42

1.31

6600

3360

280

6.9

410

860

Dry

0.44

1.63

11300

7200

550

8.3

540

1290

aWML = Work to maximum load.

Reference (56).

 

Drying and Shrinkage

Type of shrinkage

Percentage of shrinkage
(green to final moisture content)

0% MC

6% MC

20% MC

Tangential

7.8

6.3

2.6

Radial

4.2

3.4

1.4

Volumetric

12.4

9.5

4.0

References: (56, 192).

Kiln Drying Schedulesa

 

Conventional temperature/moisture content-controlled schedulesa


Condition

4/4, 5/4
stock

6/4 stock

8/4
stock

10/4
stock

12/4
stock

British schedule
4/4 stock

Lower grades

T11-E5

NA

T11-E5

NA

NA

NA

Upper grades

T12-C5

T11-C5

T11-C4

T8-A3

T8-A3

K

aReference (28, 185).

 

Conventional temperature/time-controlled schedulesa

 

Lower grades

Upper grades


Condition

4/4, 5/4 stock

6/4 stock

8/4 stock

4/4, 5/4 stock

6/4 stock

8/4 stock

12/4, 16/4 stock

Standard

291

291

291

294

294

294

288

aReferences (28, 185).

 

High temperaturea


Condition

4/4, 5/4 stock

6/4 stock

8/4 stock


Other products

Standard

400

400

400/ 415

NA

aReferences (28, 184).

 

 

Working Properties: The wood is intermediate in nail holding ability and has a tendency to split when nailed. It is satisfactory with respect to being glued and in taking stains, polish, varnish and paint.

Durability: Hemlocks are rated as being slightly or nonresistant to heartwood decay.

Preservation: Western hemlock is resistant to preservative treatment (6).

Uses: Roof decking, laminating stock, moldings, architectural trim, general construction, newsprint and plywood.

Toxicity: May cause dermatitis (5,10&16).

 

 

Additional Reading and References Cited (in parentheses)

1. Boone, R. S.; Kozlik, C. J.; Bois, P. J., and Wengert, E. M. Dry kiln schedules for commercial woods - temperate and tropical. Madison, WI: USDA Forest Service, FPL-GTR-57; 1988.

2. Dallimore, W.; Jackson, A. B., and Harrison, S. G. A handbook of Coniferae and Ginkgoaceae. London, UK: Edward Arnold Ltd.; 1966.

3. Elias, T. S. The complete trees of North America, field guide and natural history. New York, NY: van Nostrand Reinhold Co.; 1980.

4. Gerry, E. Western hemlock "floccosoids" (white spots or streaks). Madison, WI, USA.: USDA Forest Service, Forest Products Laboratory, No. 1392.; 1943.

5. Hausen, B. M. Woods injurious to human health. A manual. New York, NY: Walter de Gruyter; 1981.

6. Henderson, F. Y. A handbook of softwoods. London: HMSO; 1977.

7. Johnson, R. P. A. and Gibbons, W. H. Properties of western hemlock and their relation to uses of the wood. Washington, DC, USA.: USDA Forest Service, Technical Bulletin No.139.; 1929.

8. Little, jr. E. L. Checklist of United States trees (native and naturalized). Washington, DC: USGPO, USDA Forest Service, Ag. Handbook No. 541; 1979.

9. Luxford, R. F.; Wood, L. W., and Gerry, E. "Black streak" in western hemlock: its characteristics and influence on strength. Madison, WI, USA.: USDA Forest Service, Forest Products Laboratory, Report No 1500.; 1943.

10. Mitchell, J. and Rook, A. Botanical dermatology: plants and plant products injurious to the skin. Vancouver, BC: Greenglass Ltd.; 1979.

11. Packee, E. C. Tsuga heterophylla (Raf.) Sarg. Western Hemlock. in: Burns, R. M. and Honkala, B. H., tech. coords. Silvics of North America. Volume 1, Conifers. Washington, DC: USDA Forest Service; 1990; pp. 613-622.

12. Simpson, W. T. Dry kiln operator's manual. Madison, WI: USDA Forest Service, FPL Ag. Handbook No. 188; 1991.

13. Summitt, R. and Sliker, A. CRC handbook of materials science. Vol. 4. Boca Raton, FL: CRC Press, Inc.; 1980.

14. Taylor, R. J. The relationship and origin of Tsuga heterophylla and Tsuga mertensiana based on phytochemical and morphological interpretations. Am. J. Bot. 1972; 59(2):149-157.

15. USDA. Wood handbook: wood as an engineering material. Madison, WI: USDA Forest Service, FPL Ag. Handbook No. 72; 1974.

16. Woods, B. and Calnan, C. D. Toxic woods. British Journal of Dermatology. 1976; 95(13):1-97.

Abbreviations