Rot Resistance in Wood

Larger trees have an outer layer of living sapwood, as well as the inner heartwood. Sapwood has a number of functions, but the main function of the mostly dead heartwood is to lend support and hardness to the tree. When the conversion of sapwood to heartwood takes place, the tree deposits chemicals called “extractives,” or “resins” outside the cell wall that give the heartwood its strength, water resistance, rot resistance, and color.

The heartwood of some trees will develop structures known as “tyloses,” bulges of plant tissue that block the naturally occurring pores in trees, making the tree mostly water tight. Some of the trees that are noted for tylose formation include white oak, post oak, burr oak, beech, black locust, and honey locust. The amounts and kinds of extractives and presence or absence of tyloses is what gives wood its rot resistance. Very rot resistant woods include black locust, redwood, Osage orange, red mulberry, cedar, bald cypress, chestnut, and catalpa. Some moderately rot resistant woods include white oak, black walnut, sassafras, redwood, and black cherry. Woods that are not very rot resistant include maple, beech, hickory, ash, tulip poplar, and basswood.

Article by FCFCDB member

Nature Note for 1/27/2019