I remember as a kid with a billhook being very firmly instructed not to mess with elder when I was allowed to help trim the hedges at my grandad's. It's very bad luck. I can't remember for the moment what the consequences were supposed to be, but it had to do with the elder protecting you from bad stuff. Birds have started a couple of elders off on the edges of my own garden in the last few years, and even if they block my view or sunlight I think I'll have to let them be. After holly and willow elder's probably one of the first trees I would have been able to recognise!