It is a very odd looking growth on the elder, but I am sure its not a gall; there are no known wasp galls found on elder (and very few galls of any kind associated with it). The tree appears to be dead, so I can only think these are the old eroded remains of twiggy outgrowths on the trunk - the holes being where the soft internal pith has worn away before the hard outer layer.
It is a very odd looking growth on the elder, but I am sure its not a gall; there are no known wasp galls found on elder (and very few galls of any kind associated with it). The tree appears to be dead, so I can only think these are the old eroded remains of twiggy outgrowths on the trunk - the holes being where the soft internal pith has worn away before the hard outer layer.