Inner Trunk

Trunks provide stability, protect the inner tree,transport water and nutrients and support the crown.

Cell division in the trunk’s cambium (secondary growth) causes thickening. In all woody plants, secondary growth increases width while primary growth (cell division at root and stem tips) causes lengthening.

At the trunk’s centre is the pith. Made of spongy parenchyma cells that are ubiquitous in plants, it serves various functions including storage, secretion, aeration, damage repair and assisting photosynthesis.

All stem (trunk) wood in young trees is sapwood. It evolves during growth, however, as the tree’s need for structural support becomes greater and the increased trunk size means it isn’t all required to conduct sap.

As older rings of sapwood cells die, they are chemically transformed into heartwood, providing more stability and protecting the tree’s centre with its harder resin- and mineral-rich dead xylem cells.

Meanwhile energy storage and water transportation are left to the newer sapwood.

Sapwood and heartwood tend to be easily distinguishable due to their different shades(sapwood is usually lighter). The key difference is that sapwood is living andcan be found outside the heartwood, inside the layers of cambium and bark.

Faster-growing trees typically have thicker sapwood bands.

Image: ScienceFacts.net