What is the Difference Between Heartwood and Sapwood

The main difference between heartwood and sapwood is that heartwood is the dead, inner wood whereas sapwood is the outermost portion of a wood that is living. Furthermore, heartwood occupies a large portion of the cross-sectional area of the wood while sapwood occupies a small area. Moreover, sapwood is often light in color when compared to the heartwood.

Heartwood and sapwood are the two areas in a cross section of a woody stem. Both types of wood perform a critical function in a tree.

Key Areas Covered

1. What is Heartwood
     – Definition, Features, Function
2. What is Sapwood
     – Definition, Features, Function
3. What are the Similarities Between Heartwood and Sapwood
      – Outline of Common Features
4. What is the Difference Between Heartwood and Sapwood
       – Comparison of Key Differences

Key Terms

Durability, Heartwood, Sap Transport, Sapwood, Secondary Xylem, Structural Support

What is Heartwood

Heartwood or duramen is the inner portion of the woody stem, containing a plugged secondary xylem. The formation of the heartwood is genetically programmed. With the growth, the stem increases its diameter by forming new xylem and phloem. Therefore, the more centered, old xylem becomes useless.

Figure 1: Freshly Cross Section of Laburnum

Then, this part of xylem converts into a part with an essential function to the tree. For that, the cells of the center of the trunk die and chemical compounds accumulate in them. Some of these compounds are resins, terpenes, and phenols. Thus, this gives a dark color to the heartwood. Also, this gives it the resistance to decay and the ability to avoid insects and fungal infections. Moreover, this allows functional alteration. Hence, the main function of the heartwood is to provide structural support to the tree.

What is Sapwood

Sapwood or laburnum is the starting form of wood of any tree. It occurs from a thin layer of cells beneath the bark called the vascular cambium, which produces wood cells to the inside and bark cells to the outside. Therefore, the sapwood always contains newly-forming cells that are alive. Also, since these cells do not contain any deposited chemical compounds like resins, the sapwood is lighter in color and soft in texture. However, it is more prone to fungal and insect attacks.

Figure 2: Wood Growth and Structure

The main function of sapwood is to transport water and nutrients throughout the plant. Collectively, water and nutrients are known as the sap. Also, the cells in the sapwood provide structural support to the tree as well.

Similarities Between Heartwood and Sapwood

• Heartwood and sapwood are the two types of wood that occur in a cross section of a woody tree.
• A considerable part of both types of wood contains the secondary xylem. Also, both form from the action of vascular cambium.
• Also, both types of wood are important for the maintenance of life of a tree. They provide structural support to the tree.

Difference Between Heartwood and Sapwood

Definition

Heartwood refers to the dense inner part of a tree trunk, yielding the hardest timber while sapwood refers to the soft outer layers of the recently formed wood between the heartwood and the bark, containing the functioning vascular tissue. Thus, this is the main difference between heartwood and sapwood.

Also Called as

Moreover, another name of heartwood is duramen and that of sapwood is alburnum.

Occurrence

Another difference between heartwood and sapwood is that the heartwood occurs in the center of the stem while sapwood occurs in the peripheral region.

Cells

Furthermore, the cells of the heartwood are comparatively old, and most of them are dead while the cells of sapwood are young and most of them are alive. Furthermore, the heartwood contains densely-arranged cells while the sapwood cells are loosely-arranged. Hence, this also a difference between heartwood and sapwood.

Color

Also, the color is another difference between heartwood and sapwood. Usually, heartwood is dark in color while sapwood is light in color.

Weight

Besides, the heartwood is heavier than the sapwood.

Hard or Soft

Additionally, the heartwood is hard while sapwood is soft.

Xylem

Xylem also contributes to a difference between heartwood and sapwood. Heartwood mainly contains the dead and non-functional secondary xylem while sapwood mainly contains the living and functional secondary xylem. Furthermore, in heartwood, the lumen of the tracheids and vessels are plugged by the tyloses formation but, the lumen of the tracheids and vessels in sapwood are not interrupted.

Composition

One other difference between heartwood and sapwood is their composition. Heartwood contains more lignin while the sapwood contains more cellulose than the other.

Conductivity

Furthermore, heartwood serves as an insulator while the sapwood serves as a conductor.

Function

Their function is also a major difference between heartwood and sapwood. Heartwood is responsible for providing the structural support to the tree. In contrast, sapwood transport water, and nutrients while providing structural support. 

Durability

Moreover, heartwood is durable while the sapwood is not durable. Furthermore, heartwood is resistant to insects and fungal infections while the sapwood is more prone to fungal infections and insect attacks. Therefore, heartwood is suitable for furniture but not the sapwood.

Conclusion

Heartwood is the innermost, hard portion of a woody stem, which mainly contains plugged secondary xylem. Due to its durability, heartwood is better for furniture. On the other hand, sapwood is the outermost, soft portion of the woody stem, consisting of functional secondary xylem. The main function of sapwood is to transport sap. However, the heartwood mainly provides the structural support. Therefore, the main difference between heartwood and sapwood is the structure and function.

References:

1. “Heartwood.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 9 Feb. 2012, Available Here
2. “Sapwood.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 July 2012, Available Here

Image Courtesy:

1. “Freshly cross cut Laburnum with heart-wood” By Per Grunnet – Own work (CC BY-SA 4.0) via Commons Wikimedia  
2. “Wood growth ill” (CC BY 2.5) via Commons Wikimedia