The preservative retention levels are printed on the quality mark tag that is stapled to the end of the board. Often trees grown around the farm can be used and although not treated, many of these species will provide several years of good service. There are still several species commonly available that provide excellent resistance to decay and should last several years. Listed below are some species that have heartwood resistance to decay. The list of decay resistant woods is for the heartwood of the species only.
Trees contain both heartwood and sapwood.
The heartwood is the darker center section of cells that are no longer living, but provide mechanical support to the tree. The heartwood contains extractives, which are toxic to most decay fungi and some insects. Extractives are made up of many different substances including polyphenols, waxes, oils, resins, gums, tannins, and aromatic and coloring agents. The extractives are what give the heartwood of certain species distinct color and odor. For example, the extractives in the heartwood of red cedar give it the aroma commonly desired in blanket chests and closets.