Populus spp.
Family: Salicaceae
Aspen

Aspen (the genus Populus) is composed of 35 species which contain the cottonwoods and poplars. Species in this group are native to Eurasia/north Africa [25], Central America [2] and North America [8]. All species look alike microscopically. The word populus is the classical Latin name for the poplar tree.

Populus grandidentata-American aspen, aspen, bigtooth aspen, Canadian poplar, large poplar, largetooth aspen, large-toothed poplar, poplar, white poplar

Populus tremuloides-American aspen, American poplar, aspen, aspen poplar, golden aspen, golden trembling aspen, leaf aspen, mountain aspen, poplar, popple, quaking asp, quaking aspen, quiver-leaf, trembling aspen, trembling poplar, Vancouver aspen, white poplar

Distribution

Quaking aspen ranges from Alaska through Canada and into the northeastern and western United States. In North America, it occurs as far south as central Mexico at elevations where moisture is adequate and summers are sufficiently cool. The more restricted range of bigtooth aspen includes southern Canada and the northern United States, from the Atlantic coast west to the prairie.

The Tree

Aspens can reproduce sexually, yielding seeds, or asexually, producing suckers (clones) from their root system. In some cases, a stand could then be composed of only one individual, genetically, and could be many years old and cover 100 acres (40 hectares) or more. Most aspen stands are a mosaic of several clones.

Aspen can reach heights of 120 ft (48 m), with a diameter of 4 ft (1.6 m). Aspen trunks can be quite cylindrical, with little taper and few limbs for most of their length. They also can be very crooked or contorted, due to genetic variability. The bark of the two species can be quite variable in color and degree of furrowing. The leaves of aspen can vary from nearly round to ovate, with small to large teeth. Aspen trees are dioecious, that is, they occur as either male or female trees.

The Wood

General

The sapwood of aspen is white, blending into the light brown heartwood. The wood of aspen has a uniform texture; is straight grained, light and soft; and has good dimensional stability and low to moderate shrinkage.

Mechanical Properties (2-inch standard) ^a

				Compression
	Specific gravity	MOE GPa	MOR MPa	Parallel MPa	Perpendicular MPa	WML^a kJ/m^3	Hardness N	Shear MPa
Populus grandidentata (bigtooth aspen) ^b
Green	0.36	7.7	37.2	17.2	1.45	39	1,646	5.03
Dry	0.39	9.9	62.7	36.5	3.10	53	1,868	7.45
Populus tremuloides (quaking aspen) ^c
Green	0.35	5.9	35.2	14.8	1.24	44	1,334	5.03
Dry	0.38	8.1	57.9	29.3	2.55	52	1,557	5.86
WML=Work to maximum load ^aRelatively low strength, moderate stiffness and shock resistance. ^bReference (98) except for hardness (59). ^cReference (98).

Drying and Shrinkage

Type of shrinkage	Percentage of shrinkage (green to final moisture content)
	0% MC	6% MC	20% MC
Populus grandidentata (bigtooth aspen)
Tangential	7.9	6.3	2.6
Radial	3.3	2.6	1.1
Volumetric	11.8	9.4	3.9
Populus tremuloides (quaking aspen)
Tangential	6.7	5.4	2.2
Radial	3.5	2.8	1.2
Volumetric	11.5	9.2	3.8
aWater soaked material can develop "wetwood" from bacteria, causing a collapse in the zone between sapwood and heartwood during drying. References: 0% MC (98), 6% and 20% MC (90).

Kiln Drying Schedules^a

	Stock
Condition	4/4, 5/4, 6/4	8/4	10/4	12/4	16/4
Normal wood	T12-E7	T10-E6	T8-E5	T8-E5	T7-C4
Wet streak or collapse prone	Table 109	Table 110	—	—	—
^aReferences (6, 86).

Working Properties: Aspen does not split when nailed, machines easily with a slightly fuzzy surface, and turns, bores and sands well. It holds nails poorly to fairly well, but glues, prints, and holds paint well. It is easily pulped by all commercial processes.

Durability: Rated as slightly or nonresistant to heartwood decay.

Preservation: Extremely resistant.

Uses: Pulp for books, newsprint and fine printing papers. Fiberboard, wafer board, sheathing, decking, decorative applications, boxes, crates, pallets, furniture parts, lumber core, veneer, match sticks, tongue depressors, paneling, excelsior.

Toxicity: Sawdust may cause dermatitis (40, 64, 105).

Additional Reading and References Cited (in parentheses) 29, 55, 68, 70, 74.

6. Boone, R.S.; Kozlik, C.J.; Bois, P.J.; Wengert, E.M. 1988. Dry kiln schedules for commercial woods-temperate and tropical. Gen. Tech. Rep. FPL-GTR-57. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

29. Elias, T.S. 1980. The complete trees of North America, field guide and natural history. New York: van Nostrand Reinhold Company.

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

55. Little, Jr., E.L. 1979. Checklist of United States trees (native and naturalized). Agric. Handb. 541. Washington, DC: U.S. Department of Agriculture, Forest Service. U.S. Government Printing Office.

59. Markwardt, L.J.; Wilson, T.R.C. 1935. Strength and related properties of woods grown in the United States. Tech. Bull. 479. Washington, DC: U.S. Department of Agriculture, Forest Service. U.S. Government Printing Office.

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

68. Panshin, A.J.; de Zeeuw, C. 1980. Textbook of wood technology, 4th ed. New York: McGraw-Hill Book Co.

70. Perala, D.A.; Carpenter, E.M. 1985. Aspen, an American wood. FS—217. Washington, DC: U.S. Department of Agriculture, Forest Service.

74. Record, S.J.; Hess R.W. 1943. Timbers of the new world. New Haven, CT: Yale University Press.

86. Simpson, W.T. 1991. Dry kiln operator's manual. Ag. Handb. 188. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

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

98. U.S. Department of Agriculture. 1987. Wood handbook: wood as an engineering material. Agric. Handb. 72. (Rev.) Washington, DC: U.S. Department of Agriculture. 466 p.

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