Timber technology — anatomical zones In a timber log, what is the inner, mature region surrounding the pith commonly called?

Introduction / Context:
Timber is composed of distinct anatomical zones, each with unique properties affecting durability, strength, and treatment response. Identifying heartwood versus sapwood is crucial for selection in structural and finishing applications.

Given Data / Assumptions:

• Pith occupies the very center.
• Heartwood surrounds the pith and is typically darker, denser, and less permeable.
• Sapwood forms the outer, lighter band that conducts sap.
• Cambium is a thin growth layer under the bark.

Concept / Approach:
As trees mature, older xylem becomes heartwood, a reservoir of extractives that enhance natural durability. Sapwood remains physiologically active, transporting water and nutrients. The cambium is responsible for radial growth but is not a bulk wood zone.

Step-by-Step Solution:
Identify the region immediately around the pith: mature xylem.This region is typically darker and called heartwood.Therefore, the correct term is heartwood.

Verification / Alternative check:
Examine any cross section: central pith, then a ring of darker heartwood, then lighter sapwood, then cambium and bark.

Why Other Options Are Wrong:
Sapwood is outer, active xylem, not the inner mature zone.

Cambium is a thin cell-generating layer, not the bulk wood surrounding pith.

Bast (phloem) lies outside cambium and is unrelated to the inner wood.

Common Pitfalls:
Assuming heartwood is always stronger; species and defects matter. Confusing color differences due to staining versus true heartwood boundaries.

Final Answer:
heartwood