Komu helped me free two trees from ivy.  The ivy grew 30 feet up one tree and 60 feet up the other.  The ivy stem seen in the lower picture measured about four inches wide and had at least 16 growth rings.  Unfortunately, the alder with the most ivy also had the most decay, and it may not enjoy its freedom very long.  Hopefully the ivy will be completely dead before it falls, so it won't spread any faster than it already does.