Tree pollarding a necessary part of tree maintenance for some trees is usually carried out in winter or early spring. It is usually recommended that this is done every other year to keep the tree in the best condition possible.
Pollarding a tree removes the crown of the tree down to the main trunk. Trees can really benefit from pollarding as it gives them a good chance of survival during winter, but also healthy uniformed growth too.
This is because pollarding reduces the need for the tree to absorb water and nutrients into its canopy, which lessens the stress on the roots and makes the tree more healthy as it grows.