Many types of trees found in the Celtic nations are considered to be sacred, whether as symbols, or due to medicinal properties, or because they are seen as the abode of particular nature spirits. Historically and in folklore, the respect given to trees varies in different parts of the Celtic world, believing that each tree was an ancestor of a human being.
When the Celts cleared an area for the purposes of settlement, a single tree would be left in the centre which became known as the Tree of Life. According to the Ancient Celtic Druids, the Tree of Life possessed special powers and symbolised balance and harmony.
In Celtic mythology it is a symbol of youthfulness and rebirth. The Ash Tree. The ancient Irish believed the Ash tree had healing qualities and saw it as one of a trilogy of sacred trees. The oak is considered a cosmic storehouse of wisdom embodied within its towering strength. Ancient Celts observed the oak's massive growth and impressive expanse. There are accounts that trace the name “druid” to duir, the Celtic term for the oak. The hawthorn is one of the most sacred trees and symbolises love and protection, balance and duality. ... In May, the hawthorn is in its glory with strikingly beautiful blossoms. It is also known as the Fairy Tree, as fairies live under the Hawthorn as its guardians, and so was treated with great respect and care.