Tree EKGs

Ran into an MIT link about getting small amounts of electricity from trees and using this electricity to power monitors. It looks as if the article is based upon just a tiny mention of potential applications by the authors of a PLoS ONE paper on the method of getting electricity from trees. The idea is to have monitors powered by the trees distributed throughout a forest to detect forest fires and monitor the environment. Could you hook these up in series and generate a usable amount of electricity from a wild forest, thus placing a value on a standing forest?