According to the Daily Telegraph of 10 January 2014:
The council at Porthtowan, Cornwall, will bury Christmas trees in sand dunes to prevent them being eroded by the sea:
‘The discarded trees will bind the dunes and create a habitat for wildlife once marram grass [Ammophila arenaria] seeds are planted in the spring.’
However some villagers dismiss the plan as a ‘crackpot idea’.

Image: thrown out Christmas trees, Bedford Hill, Balham, London Borough of Wandsworth; January 2014.