These Trees are Electric

One might not have considered that trees could produce electricity, but they actually can.  Differences in pH levels between a tree and the soil in which it grows can create small electric charges (very small really, measured in millivolts).  Still some scientists at MIT are using these small charges to develop sensors that can take readings (like temperature or humidity) from within forests.  Read about their work and more about tree electricity in this Discovery
News Article.