Hi
I am researching grike microclimates and therefore will be leaving equipment in the field for an extended period of time. To stop this being stolen and ruining my results should I advertise its presence and rely upon the good will of people not to pocket my data loggers, or alternatively hide their presence and run the risk of people helpfully clearing away the expensive equipment cluttering up the site.

I think it would depend what type of land you're putting it on.  I'm guessing you will already have permissions from land owners or public bodies etc to put your equipment onto the land?

If it's a heavily used site i.e. a public nature reserve or near a footpath I think there will be risks for theft or vandalism either way.  Perhaps attempt to hide it but put a note on the equipment explaining what it is so that if people come across it they will be less likely to move it? As long as you know where it is so you can find it again
:p