The best part of the wood, in terms of overall quality and performance, is typically the heartwood. Heartwood is the central, denser portion of the tree, which is formed after the tree has reached maturity. It is characterized by its darker color and higher density compared to the lighter, softer sapwood. The heartwood is preferred for its durability, strength, and resistance to decay and insects.

The reason heartwood is superior lies in its unique cellular structure and chemical composition. Heartwood cells are larger and more tightly packed than sapwood cells, which contributes to its greater strength and density. Additionally, the heartwood contains more natural resins and tannins, which act as natural preservatives, protecting the wood from decay and insects. According to the Forest Products Laboratory of the United States Department of Agriculture (USDA), heartwood is up to 20% harder than sapwood, making it more suitable for structural applications and furniture.

Data from the USDA's Forest Products Laboratory indicates that heartwood has a higher modulus of elasticity (MOE) and modulus of rupture (MOR) compared to sapwood. MOE measures the wood's ability to resist bending, while MOR measures its ability to resist breaking under tension. These properties make heartwood ideal for use in construction, flooring, and other applications where strength and durability are crucial.

Furthermore, heartwood's resistance to decay and insects is a significant advantage. This is particularly important in outdoor applications, such as decks, fences, and outdoor furniture, where the wood is exposed to moisture and pests. The presence of natural preservatives in heartwood helps to extend the lifespan of the wood, reducing maintenance costs and ensuring long-term performance.

In summary, the heartwood of a tree is the best part for its superior strength, durability, and resistance to decay and insects. Its unique cellular structure and chemical composition make it the preferred choice for a wide range of applications, from construction to furniture making.