Thursday, April 7, 2016
Why we call it sapwood
This high flow of sap from the outer-most layers of wood is the origin of the term "sapwood". However, the term sapwood means something entirely different to those that cut pecan trees for lumber. The sapwood refers to the lighter, almost white colored wood on the outer portion of the trunk. The heartwood of pecan trees is found in the center of the tree and is typically brown in color. You can see darker colored heartwood at the far right in the photo above.
Outside the wood is a narrow band of cells called the cambium (red arrow above). Every spring these cells become active creating new wood cells on one side and new bark cells on the other. The activity of the cambium layer is responsible for the tree's annual increase in diameter.
On a mature pecan tree, you will find two distinct layers of bark. The inner bark or phloem functions to transport carbohydrates from the leaves downward to all other portions of the tree (branches, trunk, roots). The outer bark provides protection for the living tissues underneath. The outer bark acts as a vapor barrier to prevent moisture loss and as insulation against heat and cold.