Heartwood vs Sapwood
Heartwood is the dense, dark inner core of a tree trunk that no longer transports water or nutrients, while sapwood is the lighter-colored outer layer that actively conducts sap. Heartwood gets its color from extractive chemicals that also provide natural decay resistance. Sapwood is lighter in color and generally more susceptible to rot and insect attack.
In-Depth Explanation
As a tree grows, the older inner rings of sapwood gradually transform into heartwood through a process where the living cells die and the tree deposits extractive compounds — tannins, resins, and oils — into the cell walls. These extractives darken the wood and make it resistant to fungal decay and insect damage. The proportion of heartwood to sapwood varies greatly by species: black walnut has a small sapwood band and large heartwood core, while maple has thick sapwood with relatively little heartwood color differentiation. For outdoor applications like decking, fencing, and siding, heartwood of naturally durable species (cedar, redwood, white oak, black locust) is preferred because it resists rot without chemical treatment. Sapwood, however, is actually preferred for pressure-treated lumber because its open cell structure readily absorbs preservative chemicals, while heartwood's extractives can resist preservative penetration.
Usage Example
The homeowner specified all-heartwood western red cedar for the fence because the sapwood boards would rot within a few years without chemical treatment.