Blame the ELF's

While doing research for a story, I ran across more detailed information about Project ELF (alternative link) than the news ever carried. Part of the technology is apparently still secret, but it looks like they were trying to use granite bedrock as part of the antenna. It wasted a lot of power, but it worked. At these frequencies (76Hz) people's claims of hearing a "hum" seem plausible. I don't know about claims of harm -- I generally discount those unless there's a clear physical model to connect them -- but this was curious:

On the other hand, faculty and researchers at the Michigan Technological University (MTU) School of Forestry and Wood Products have found that the Project ELF’s antenna grid makes the trees grow faster. MTU foresters have been studying the effects ever since the system became operational ten years ago.

The forester's final report says "subtle EM effect to the cambial and stemwood growth of some tree species but not to any other parameter". They claimed a relationship between "diameter growth and magnetic flux density" for aspen and red maple, and "annual height growth and magnetic flux density" for red pine.

That looked like an increase when the field was O(2-3mG), dropping off to "normal" for higher exposures. My first guess when seeing something that only effects a few species is a "look-elsewhere effect", but there's enough similarity that maybe it's worth looking at in more detail. I wonder what the conductivity of the sap is in the different species.

Squirrel!

Yes, I know there can be confounding factors, like distance from a cleared area (they look at that) or herbicides