The primary term for the body of a tree is the trunk. This sturdy, woody structure is the fundamental support column for the entire plant, connecting the root system to the branches and leaves. The trunk acts as the central axis, providing the strength necessary to withstand environmental forces like wind and gravity, while also transporting essential resources.
The Tree’s Central Structure
While “trunk” is the most common term, the body of a tree can also be called a “bole” or a “stem.” “Stem” is a broader botanical term for the main stalk of any plant, but it refers to the trunk in a mature, woody plant. The word “bole” specifically describes the main trunk section before it branches out, often used when discussing timber.
The trunk’s main responsibility is to elevate the crown, allowing the leaves to capture sunlight efficiently for photosynthesis. This central column facilitates the movement of water and dissolved minerals upward from the roots. It also channels the sugars produced in the leaves downward to nourish the roots and other parts of the tree.
The Protective Outer Layer
The external covering of the trunk is the bark, which serves as the tree’s armor. Bark is a collective term for all tissues outside the vascular cambium, the layer responsible for growth. It consists of two main components: the outer bark (periderm) and the inner bark (phloem).
The tough outer bark is composed of dead cork cells, forming a dense, insulating layer. This layer shields the delicate inner tissues from physical damage caused by animals, insects, and debris. It also prevents excessive water loss through evaporation and provides insulation against temperature changes and low-intensity ground fires.
Anatomy of the Trunk
Moving inward from the bark, the trunk’s anatomy reveals layers dedicated to growth, transport, and support. Directly beneath the inner bark is the vascular cambium, the primary growth tissue. The cambium is responsible for the tree’s increase in girth, producing new phloem cells toward the outside and new xylem cells toward the inside each growing season.
The bulk of the trunk is wood, which is the technical term for xylem tissue. The outermost layer of wood is the sapwood, consisting of the youngest, living xylem cells. Sapwood’s primary function is to transport water and dissolved nutrients from the roots up to the leaves. This upward movement occurs through tube-like cells that form a continuous network.
As the tree ages, the innermost layers of sapwood cease to transport water and become denser, forming the heartwood. Heartwood is non-living but provides the majority of the trunk’s structural strength, acting as the central pillar. This layer often becomes darker than the surrounding sapwood due to the deposition of materials like resins and tannins, which increase its resistance to decay and pests.