Tree Spirits and the Supernatural Nature of Trees
Each country has tales of sprites and goblins, of localised and guardian spirits. Every field or stream, forest or bare mountain top had its strange inhabitants, jealously guarding a treasure or secret. If a forest had a supernatural guardian, it is not much of a leap in logic to assume that the trees themselves had a supernatural connection.
Trees also formed an important part of Celtic worship. This is not surprising since many sacred groves served as religious centres throughout the Celtic world. The ancient perception of trees in such places may have given them a particularly sacred significance.
Trees also acted as pillars that stretched from earth to sky, into the realm of the gods/spirits. From earliest times men looked on trees as a kind of 'bridge' between the two realms.
Solitary trees in particular often resembled grand columns stretching up towards the sky, the home of the spirits. Powell (The Celts 1958) postulates that for the Celts, lone trees represented a 'cosmic pillar' on which the spirits could travel down to visit their worshippers below. He goes on to speculate that the Jupiter-columns of Classical temple architecture have their origins in wood, perhaps even in the growing of a sacred tree within the enclosed precincts. Certainly, Celtic tree worship combined well with the perceptions of many other ancient faiths.
The oak was sacred to the Roman god Jupiter (in some parts of the Roman world it was also sacred to Mars, the war-god) and sometimes to Woden, the supreme Norse god. At some point in their religious history the Celts appear to have started to worship trees in their own right. There are a number of sites, particularly in Ireland, that suggest that trees were worshipped there in former times. Magh-Bhile (Moville in Co Donegal) means the 'plain of the worship of the old tree'; Derry (Northern Ireland's second largest city) is derived from the name Doire or Dair meaning oak-tree; Kildare from Cill-Dara, the 'church (or cell) of the oak'.