In The Music of the LOTR Films, Doug Adams identifies three themes associated with The Ents.

THE ENT THEME - The music of the Ents is informed as much by the instruments used as by any melody. Shore used a collection of wood instruments, bassoon and low basses that play meandering melodies that evoke mass and mystery. The music moves with a slow but deliberate cadence.  

TREEBEARD'S STRIDE- A two chord motif for Treebeard and the forest. For more information, see The Music of the LOTR Films.

SMALL STONES - A four chord motif that highlights Merry and Pippin's association with and effect on the Ents. For more information, see The Music of the LOTR Films.