Wrapping birch

Last year some of the ewes took a liking to birch bark and a few of the trees have died as a result.  So this year we are wrapping the trunks in plastic tubes.  These are the tubes that were originally used when we planted the saplings (15 years ago).  Fortunately we didn't get rid of them. I doubt if we will wrap up all the trees (approx 600) but we've protected around 50 which are closest to the sheep shed.  We have fenced off a small area for the lambs when they arrive and we will gradually extend the area as we have done in previous years.