I could design something that would work, but I don't know how economical it would be.
You'll only need this for a few weeks/a couple of months while the sap runs, right?
Everything could run off batteries, but there are few communication devices that would let you run a remote Internet connection for a month without some kind of recharge.
Is the site line-of-sight to something you own, or are there hills in the way? Can you get LOS communication? How far is the site from power/LOS?
Standard "ethernet" can be run using outdoor cable for up to 100 yards, and temperature and humidity aren't so localized that you shouldn't be able to set up some kind of weather station near where you want to be. Serial and USB cables should never exceed 10 yards without 'regeneration'.
I guess, really, that a lot depends on the real numbers and conditions. The terrain will determine the communication medium, and that will determine what kinds of temperature and humidity sensors would be appropriate.