The pruning of the lower branches of this tree has resulted in vertical growth. There are many examples of them in Petersham Park, Sydney, Australia. What a journey we have been on this morning, to find out the definition of this form of pruning! Is it coppicing or pollarding? The Ultimate Practical Guide To Pruning and Training by Richard Bird and multiple Google searches confirm the following:

• Coppicing is the cutting back almost to ground level of all the main shoots of a multi-stemmed tree. 
• Pollarding is exactly the same except the cutting takes place at some height above the ground. 

Why do it? 

This traditional technique enables the growth of larger trees in a small space as well as producing good foliage. The variety of tree and frequency of pruning determines the thickness and most appropriate use for the timber. Thinner frequently pruned Willow branches can be used for basket weaving while thicker Oak branches produced by longer period between prunes can be used for construction.