This green, tunnel arch is a pleached allee made up of 120 upright hornbeams.  Allee is the French word for avenue. Pleaching is the method of tying and interlacing flexible young shoots on a supporting framework to create walkways, arbors and arches.  

Such structures are commonly found in landscape designs of grand European gardens such as those at Versailles. The Allee creates a different perspective for visitors walking between gardens. Instead of merely walking across a field, the enclosed area creates a different perception of space and a sense of anticipation.