Here's a little known fact:
Approximately 60% of all assessments are too high. This is because people usually don't bother to check, so they can get away with it.
Go see your assessor on grievance day, usually in May sometime. They tax you at different rates for wooded land, tillable, waste land, etc. We got ours lowered a few years ago by convincing him that our fields were wasteland, since they hadn't been in production since we moved here. We're letting them grow up to good deer habitat.
Also, if you're not getting the STAR exemption, see if you can sign up for it. I'm not sure if it applies to vacant land, but we saved over $500 this year with it.
As for your tree farm idea, I believe you can plant them for about 5 years and take the write offs, but then you have to start selling them. The IRS gives you 5 years to start making money before they consider it a hobby and make you pay back all the write offs you took the previous years. Talk to your accountant, he can probably tell you what's required.