What is a tree?

Everyone knows a tree when they see one, but describing precisely what a tree is can be tricky. The generally accepted definition of a tree is that it is a plant with a more or less permanent shoot system that is supported by a single woody trunk.

Trees are the tallest free-standing organisms in the world. They live longer and become larger than any other living organism on earth. With more than 80,000 species growing worldwide, they come in all shapes and sizes; from tiny Arctic Willows a few centimetres high through to giant Redwoods over 100 metres tall.

Trees differ from shrubs. Shrubs normally branch near the ground and sometimes have several narrow stems rather than one single trunk. Having several stems means a shrub can support many leaves but their overall structure is less rigid than one single, thick tree trunk.

Single stemmed tree Shrub showing multiple stems
Single stemmed tree
© Debbie Cotton
Shrub showing multiple stems
© Forestry Commission