PS -
If you read MagCap's actual press release, you will see on page 4 a description of the "invention".
"Simply drive an aluminum roofing nail through the bark and into the wood of a tree – any tree – approximately one half inch; drive a copper water pipe six or seven inches into the ground, then get a standard off-the-shelf digital volt meter and attach one probe to the pipe, the other to the nail and you’ll get a reading of anywhere from 0.8 to 1.2 volts of DC power.”
This was "dirty" power, so they rigged up a series of three capacitors in order to smooth out the current draw. With this arrangement, they got out approximately 2 volts of current.
Interesting number, "2 volts". The electric potential of reducing copper (the pipe) is +.34 volts, while the electric potential of oxidizing aluminum is -1.66 volts. Do a little math on the differential: (.34v) - (-1.66v) = 2 volts. Fancy that!
Believe me, if "tapping" the electrical potential of non-animal life forms (that's how MagCap puts it) was as simple as driving a nail into a tree and tying it off to a copper tube, we'd have been powering Atlanta that way for the past 100 years. Read the press release yourself - it's full of crackpottery.
Even if you drank the kool-aid and believed you were actually drawing down electrical energy from the plant, rather than from the nail, wouldn't this be harmful to the plant? Presumably, that electrical current would be there for a purpose (as are the human body's various weak electrical currents, which are used to do non-trivial things like keeping our hearts beating). Also, some process would have to be in place to generate that electricity - presumably some sort of solar power conversion. Considering that most of that solar energy is going into keeping the plant alive and growing via photosynthesis, it stretches the imagination that it would have a whole bunch of "leftover" energy that it would turn into electricity just so we could harvest it. What evolutionary pressure was working on trees to push them into being stationary electrical generators?
There really is nothing to see here, folks.