Some science behind the scenes

Wood

Wood is a hard, fibrous tissue. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is produced as secondary xylem in the stems of trees (and other woody plants). In a living tree it performs a support function, enabling woody plants to grow large or to stand up for themselves. It also mediates transfer of water and nutrients to the leaves and other growing tissues.

The earth contains about one trillion tons of wood, which grows at a rate of 10 billion tons per year.

And wood is a transducer because of its cellulose content as well as its resinous content.

Piezoelectricity of biopolymers - Fukada E; Kobayasi Institute of Physical Research, Tokyo, Japan.
The piezoelectricity of semicrystalline biopolymers was first discovered for wood and bonein the 1950's.

History and recent progress in piezoelectric polymers - Fukada E; Kobeyasi Inst. of Phys. Res., Tokyo, Japan.
Electrets of carnauba wax and resin have exhibited good stability of trapped charges for nearly 50 years. …... Since the 1950s, shear piezoelectricity was investigated in polymers of biological origin (such as cellulose and collagen).

If we apply some pressure to the wood of a tree by tapping it or gently knocking it or surrounding it by sound, then the transduction effect will create a small low intensity electric current.  There also seems to be anecdotal evidence that the movement of the tree itself in high winds can also produce a current…………….

Internet site on green energy
I've seen anecdotal evidence that a tree quaking in the wind …can build up a low very current flow to ground. …... By holding a field strength meter near the trunk you can at times (depending on how wet the cambium layer is and on wind) detect the tree's own EMF emanations very close to the trunk. It is very low potential however, just a few milligauss above ambient and easily confused with instrument drift or other EMF sources.