The Yew

The yew, which has an exceptional longevity - several examples are over two thousand years old - has  a deep and sacred connection with immortality and eternal life. It is also the tree of death, not least because all parts of it are deadly if eaten.
 The custom of planting it around churches and graveyards predates Christian times by at least a millennium: the Celts planted yews around burial mounds and along sacred ways. It perhaps aided a soul's journey into eternal life.
The three witches in Macbeth used 'slips of yew, slivered in the moon's eclipse' in their magical potion, and some say the tree can cause visions of fairies.
On a more prosaic note, the wood was used to make bows and spears until recent times. The oldest discovered wooden artefact in the world is a spear made of yew, 250,000 years old. Another yew spear, slightly more recent, was found embedded in the ribs of a skeletal elephant.
This tree has perhaps the oldest association with ourselves, as befits its immortal nature.

The Ash

The ash is one of the crowning trees of the British countryside. It grows tall, straight and strong and its grey bark makes it instantly recognisable.
Its qualities make it ideal for spear-making, hence its old name of 'weapon-wood'. TheAnglo-Saxon word 'aesc' meant both ash and spear. It was also used for wheel spokes.
Another characteristic is its stability: the tree rarely topples in even the worst winter storm. The Saxons believed that its roots were anchored into the underworld itself, and so the ash became the symbol of the World Tree, known to the Scandinavians as Yggdrasil and myriad names to other worldwide cultures,  which links Earth with the realms of the Gods.
A 'maiden' ash, self-sown and never pruned, was especially powerful. Its wood would ward off magical harm, and so was carried by riders to protect their horses, and a wizard's magic wand was also often ash.
Next time, another magical tree.