Pollarding means cutting back to roughly the shape and size of a person - maybe bigger and certainly thicker, if it's an old tree. Polls can live for many hundreds of years and are supposed to be an ancient means of producing green forage material for stalled cattle, amongst other things. I'd be surprised if the complex art of pollarding had survived in Wiltshire - but, please, prove me wrong - coppicing has. Anything else is called 'slashing' and is one half of the agricultural system known as 'slash and burn'.