When a tree is pollarded the branches are cut off. This encourages a dense head of young branches. Over time, the trunk of the tree becomes old and gnarled and a haven for wildlife. In the past trees were pollarded to generate useful wood products such as poles. The type of wood crop required dictated how long the crown was left without pollarding. These willows have been pollarded every April for about 20 years but they still have a long way to go before they develop interesting trunks.