The Swiss Federal Institute for Forest Snow and Landscape Research WSL

Ring of life

Transport of water and nutrients

Water and nutrients are transported in the lighter, outer wood. The darker, harder wood no longer has any active cells and serves for the stability of the trunk.

The light outer area, known as the sapwood, is the trunk’s active zone. Its function is to store water and nutrients and transport them to the crown, up to the needles.

In larch, after a certain time, sapwood turns into the inactive heartwood. This darker trunk area is more resistant to insects and fungi because of various substances, but it no longer contains living cells.

Young branches consist only of sapwood, while the amount of heartwood increases in older branches and towards the trunk base. In some tree species, such as black locust or oak, the trunk contains only a few sapwood rings, while other species such as larch, spruce, birch or maple have dozens of sapwood rings. Due to the substances stored in it, heartwood is more resistant to weathering and is therefore appropriate for outdoor uses in carpentry.