The common confusion surrounding wood classification often stems from applying the physical property of hardness to botanical categories. Many people assume that a wood must be a “softwood” if it is easily dented or a “hardwood” if it is dense, but this is not the case. The terms “hardwood” and “softwood” are definitive botanical classifications based on the tree’s reproductive structure, not the strength or density of its lumber. Understanding this distinction is necessary to categorize species like Hemlock correctly.
The Definitive Classification of Hemlock
Hemlock, which belongs to the genus Tsuga, is definitively classified as a softwood. This designation places it within the botanical group known as Gymnosperms, which are cone-bearing plants. Hemlock species, such as Eastern Hemlock (Tsuga canadensis) and Western Hemlock (Tsuga heterophylla), produce cones and needles rather than broad leaves and flowers. This reproductive characteristic instantly assigns it to the softwood category.
The confusion typically arises because Hemlock wood has a moderate density that is superior to many other softwoods, occasionally leading people to mistake it for a hardwood in practical use. Its mechanical properties, including its stiffness and strength, often allow it to perform better in certain applications than some woods that are technically classified as hardwoods, such as Basswood or Aspen. However, wood classification is strictly anatomical, meaning the tree’s biology overrides the wood’s density.
The Botanical Difference Between Hardwood and Softwood
The true distinction between hardwood and softwood is rooted in the method of reproduction and the resulting cellular structure of the wood. Hardwoods are Angiosperms, which are flowering plants that produce seeds enclosed in a protective casing, such as a fruit or nut. These trees generally have broad leaves and are often deciduous, shedding their leaves seasonally.
Softwoods are Gymnosperms, meaning they are non-flowering plants that produce “naked” seeds, typically found exposed on cones. These trees are usually evergreens with needle-like or scale-like foliage. Microscopically, hardwoods possess vessel elements, which are specialized cells that transport water and nutrients, giving the wood a porous appearance. Softwoods lack these vessels, instead relying on simpler cells called tracheids for water conduction, making them non-porous.
Physical Properties of Hemlock Wood
As a softwood, Hemlock wood exhibits a relatively simple cellular structure, which is typical of Gymnosperms. A notable feature of Hemlock is the absence of resin ducts, which distinguishes it from many other commercial softwoods like pine and spruce. This lack of resin or pitch contributes to its excellent finishing and gluing properties.
Hemlock has a generally straight grain and a texture that can be uneven or coarse, especially in Eastern Hemlock. The wood is moderately light in weight, yet it possesses a good strength-to-weight ratio, making it a valuable material in construction. It is commonly used for light framing, sheathing, subflooring, and pulp for paper production.
Durability and Use
While Hemlock machines well and is used for interior millwork and furniture in some regions, it is rated as non-durable. Because it is susceptible to decay and insect attack, it requires preservative treatment for external use.