Don't know why I didn't occur to me before
but for anyone interested in how pollarding is still being used through Europe visit
http://www.woodland-trust.org.uk/anc...elendiary2.htm and whilst you're there hunt around the web site its full of fantastic info on the management of ancient trees across the world not just UK. One of the best websites running on tis subject IMHO.
The diary running on the practice of pollarding in Europe may not answer all your questions but its great to see how some of these magnificent trees are being maintained for future generations to enjoy.
Sean