An inherent power of Elf-kind, which allows an Elf to communicate with plant life. It appears to require some kind of physical contact between the plant and the Elf.
In "The Thin Line," there is a great deal of discussion regarding the tactical military uses of this power, in terms of reconnaissance. There are also two sequences in which the Voice of the Forest is revealed to a character, once when "Uncle" lays paws upon Westersloe Winterbough V, and once when Winterbough does the same for Meadow Grainmaster.
In "The Ballad of Adler Young," the power is revealed to then-Adler Fitzgawain by his mother, Mavis MacFogg, and Adler is seen using the power on a number of occasions, including a sequence when bandits lead his party astray through magicks. Adler is seen invoking the power by placing his paw against a tree trunk.