Recently I was asked the difference between Western and Eastern Hemlock. Many of us from New England know that Eastern Hemlock (Tsuga canadensis) is an evergreen with short, flat needles and it is a native of the Eastern U.S. and adjacent Canada. It grows as far west as eastern Minnesota and south to the mountains of northern Georgia.
It is extremely shade tolerant which allows it to hang around and finally take off when other competition dies off, thus becoming a "climax" specie. At maturity, Eastern Hemlock can reach large size and great age: the record is 988 years old, 84" diameter breast height, and 160' tall. The lumber is used primarily for beams and other structural building members. It is strong, heavy, and unfortunately the grain separates and wood sections can lift. I remember walking in stocking feet on my sub floor and getting bloodily impaled. Shake, or ring separation, is very common.
The Western Hemlock (Tsuga heterophylla) is similar in many respects but produces superior lumber. It is more even-grained with narrower rings, has a more gradual transition from earlywood to latewood, and a finer texture. The specific gravities are close: .40 for Eastern and .44 for Western. At building centers, Western Hemlock and Western Firs are lumped into a single commerical grade designation "HEM-FIR" because their properties are similar enough to be used interchangeably.
Western Hemlock grows along the Pacific Coast from Alaska to Northwestern California and east to Northern Idaho and Montana. Under ideal growing conditions, the trees grow to 3' - 4' diameters and 175' - 225' tall. Larger trees exist, but those over 5' in diameter are rare. Like Eastern Hemlock, it is also very shade tolerant and is a "climax" species.