Bark protects the living tissue inside a trunk from insects, fire, drying winds, and disease.

The longer version

Outer bark is made of dead cells packed with tough, water-resistant material, so it can be thick and rugged without costing the tree anything to maintain. Beneath it, a thin layer of living cells produces new bark each year as the trunk expands.

The layer shields the delicate tissue that carries water and sugar just inside it. Wounding exposes that tissue, which is why a break in the bark matters. Thick bark also insulates against fire and against rapid drying, and its texture and chemistry discourage insects and infection. Different species carry bark of very different thickness, and the difference reflects the hazards each one faces.

Where this entry sits

Plants and Trees gathers ordinary and surprising details about how green things live, from the tallest forest giants down to the moss on a garden wall. Expect notes on flowers, seeds, roots, leaves, fungi, and the quiet tricks plants use to spread and survive. The full list sits on the Plants and Trees page, where every entry is listed in order.