I read a recent online article relating to energy harvesting that reports some findings of electricity produced by a tree, i.e., a potential difference between the tree and the ground. Specifically, it is reported that University of Washington (Seattle) researchers recently demonstrated a nanoscale "boost converter" that integrates the ultra-low-voltage potentials generated by trees.
Tradition from old times in Japan credits that the potential (it is called “positive life force”) gathers in a mass of charcoal chips or powder and is good for health of a human as well as the environment in the vicinity. According to the findings of “injured potential in earth” by Mr. Satsuki Narasaki (1899-1974), a Japanese physicist, the potential can increase in earth when injuring the earth by digging a pit and then charcoal powder of high purity (pure Japanese cedar based charcoal powder) fully fills in the pit and it is covered with earth. Such findings have felt into oblivion for most as a phony, but the minority has experienced to date for themselves the presence of this strange phenomenon.
A large number of tests according to Narasaki findings has been studied and reported before. For instance, one electrode stuck into earth (about 2 inch in depth) and another into earth in more depth (about 10 inch in depth), in any case, both electrodes in earth are placed above the pit (a square about 60 inch on a side) filled with charcoal powder (about 240 pounds), compacted with water over powder and then covered with earth. The potential difference between them was measured at about 120 mV initially. Two months later, it shows 242 mV when measured again. Further, it is reported that the potential difference was measured continuously between those levels even after that.
From other point of view, it is known that the charcoal made from woods contributes both the fertile ground and the CO2 fixation in earth (“carbon negative”). Therefore, I think one electrode in the tree and another in earth above the pit being filled with charcoal powder may be a good idea to circulate the green-tech energy system and to change the trees to the credit, i.e., “carbon negative” for a debt, i.e., “carbon emissions”, and then a mini-power plant as well as a power collection system when they connect with each other.
Nothing venture, nothing win. Have a try! Here, I recommend using charcoal powder produced by my friend in Nanmoku-village at Gunma-pref. (near northwest of Tokyo) in Japan for your experiments. High quality charcoal powder is a specialty of this village.
Incidentally, do you consider harvesting the power (electricity) from vibrations of a tree by wind in windy locations? If a gyroscopic power generator such as “STABILITY ANALYSIS OF GYROSCOPIC POWER GENERATOR” published in “Proceedings of PowerMEMS 2008+ microEMS 2008, Sendai, Japan, November 9-12, (2008)” can be downsized by the latest micromechatronics and a large number of mini-gyroscopic power generators can be installed in the tree (and in more vibrant branches), I anticipate more feasibility of energy harvesting like the production of electricity from wave-motion energy off the coast (see below, study of Kobe University).
Electricity can be used for a sensor network of self-diagnosis of trees, into each of which trees a sensor for self-diagnosis is installed and operated by electricity self-generated, and it can be utilized for the study of thigmomorphogenesis and mechanoperception in trees (see, http://www.plantbiology.msu.edu/faculty/faculty-research/frank-w-telewski/ Prof. Frank W. Telewski, Department of Plant Biology, Michigan State University, is an expert in this field). The goal of this study is summarized in “Ecosystem Adaptability” (see http://gema.biology.tohoku.ac.jp/01gcoe_e.html , study of Tohoku University). In any case, no more bulky and expensive wind turbines (it is reported that the wind turbine may cause symptoms to a human in the vicinity, i.e., hypersensitivity due to the swish sound at low frequency from its vane)! … it may be a layman’s way of thinking.