SUMMARY

The Secret Tree Behind the Bark

From the outside, it's all leaves and bark, but inside there are five kinds of wood hard at work.

OUTER BARK protects the tree from weather, insects, disease, fire and animals just as your skin protects you. The bark of a birch tree may be as thin as 1/4 inch, while a giant sequoia's bark may be as much as two feet thick.

INNER BARK carries food down from the leaves to branches, the trunk and roots for growth and storage.

CAMBIUM is a layer of cells that divide and grow to produce new layers of bark and wood each year. Thanks to the cambium, you can tell the age of a newly cut tree by counting the "annual rings" of its trunk - one light and one dark will be made each year.

SAPWOOD transports minerals and water up fromthe roots to the crown of the tree. Sapwood can hold a lot of water. The African baobab treemay have a trunk up to 90 feet around andcan store up to 25,000 gallons of water. The chemicals in sap determine thecolor leaves turn in fall. Each treehas different chemical mix, soeach has its own fall color.

HEARTWOOD is the hard, inactive center of the treethat gives strength to thetree so it can stand straight.

*Graphic courtesy of North Carolina Forestry Association