Apologies if this is too far off topic but the new series The Trees That Made Britain beginning on BBC2 this Friday looks interesting (and may bring up some megalithic connections). The first of eight episodes takes a look at the yew, and especially the one in Fortingall churchyard, Perthshire, which is estimated to be 5,000 years old (and among one of the world's oldest living organisms).
Next week's episode looks at the oak.