Differences Between Sapwood and Heartwood

What is Sapwood?

Sapwood, also known as alburnum, is the outer, lighter-colored layer of wood found in a tree, situated between the bark and the heartwood. It is composed of living cells, including vessels and fibers, and plays a crucial role in the tree’s physiological processes. Here are some key characteristics and functions of sapwood:

Function:
- Sapwood is primarily responsible for the conduction of water and dissolved nutrients from the roots to the leaves. This transport is essential for photosynthesis and the overall health of the tree.
- Additionally, sapwood serves as a storage area for food and nutrients that the tree needs for growth and development.
Structure:
- Sapwood typically has a radial thickness ranging from 4 to 6 cm (1.5 to 2 inches), though this can vary depending on the species and environmental conditions.
- The cells in sapwood are alive and actively engaged in physiological activities, which distinguishes it from the inner heartwood, where the cells are dead.
Growth:
- As trees age, new layers of sapwood are formed beneath the bark, contributing to the tree’s growth in diameter. Over time, older sapwood may die and transition into heartwood, undergoing various changes in structure and function.

What is Heartwood?

Heartwood, also known as duramen, is the central, often darker part of a tree’s wood, located beneath the sapwood. It is composed of dead cells that no longer participate in the tree’s physiological functions, such as water and nutrient conduction. Here are some key characteristics and functions of heartwood:

Structure:
- Heartwood is typically denser and darker than sapwood due to the accumulation of various compounds, such as resins, phenols, and terpenes. These compounds give heartwood its distinctive color and enhance its durability.
- The formation of heartwood occurs as sapwood ages and the living cells die off. This transition results in a reduction of moisture content and a decrease in the ability to conduct water and nutrients.
Functions:
- Mechanical Support: The primary function of heartwood is to provide mechanical support to the tree. It contributes to the structural integrity and stability of the trunk, allowing the tree to withstand environmental stresses like wind and heavy snow.
- Resistance to Decay: Heartwood contains extractives that enhance its resistance to decay and insect attacks. This quality makes it a valuable resource for various applications, including construction and furniture making, where durability is crucial.
Economic Importance:
- Due to its strength and resistance to degradation, heartwood is highly sought after for timber production. It is commonly used in high-quality furniture, flooring, and construction materials.
- Additionally, certain types of heartwood, such as that from Haematoxylum campechianum, are sources of valuable compounds like haematoxylin, which are used in dyeing and histology.

Similarities Between Heartwood and Sapwood

Both heartwood and sapwood, despite their distinct functions and appearances, share fundamental similarities in their structure and development within the tree. Understanding these similarities helps clarify how they collectively contribute to the overall stability and function of the tree.

Both heartwood and sapwood are composed of secondary xylem, which forms through the process of secondary growth that occurs over many years.
They both originate from the vascular cambium, a layer of meristematic tissue responsible for the production of new xylem cells during growth.
Although heartwood primarily provides mechanical support, both heartwood and sapwood contribute to the structural integrity of the tree, offering mechanical strength that supports the plant throughout its life.