MIT researchers are experimenting to see if electricity generated by trees can power a network of sensors to prevent forest fires from spreading.

The scientists said Tuesday that their pilot system produces enough electricity to allow temperature and humidity sensors to wirelessly transmit signals four times a day, or immediately if there's a fire.

Forestry officials often rely on remote-controlled weather stations to transmit local climate data used in fire prediction models. But it's expensive and difficult to recharge or replace the batteries that power isolated stations.

Tapping into the tiny amounts of electricity produced by trees can recharge batteries automatically, cutting costs and increasing fire surveillance, say the scientists.

A single tree doesn't generate a lot of power, but over time the "trickle charge" adds up, "just like a dripping faucet can fill a bucket over time," Shuguang Zhang, associate director of MIT's Center for Biomedical Engineering in Cambridge, Mass., said in a release.

Scientists have long known that trees can produce minute amounts of electricity. But no one knew exactly how the energy was produced or how to take advantage of it.

Zhang and his co-authors reported the answer in the August issue of the Public Library of Science ONE: the energy comes from an imbalance in pH (potential of hydrogen — the measure of the acidity or alkalinity of a solution) between a tree and the soil in which it grows.

"[The] sustained voltage difference routinely observed between parts of trees and soil is mainly due to a difference in pH between the two. Specifically, the tree-root-soil system acts as a concentration pH cell," the authors write.

The scientists plan to test their tree-powered wireless sensor network this spring on land owned by the United States Forest Service.