It became a niche segment in the real estate. The idea is you find land that is cheap, but you have a feeling it has mineral wealth. You buy it cheap, get the survey done, and show that it was really worth a lot more. But instead of building a mine/oil well, you declare the land undeveloped for perpetuity. The tax benefit you receive is commensurate to the (now highly increased) value of the land.
You make a profit this way, and the environment benefits.
It's a very risky part of real estate. There are lots of environmental groups who closely monitor the land, and will file a lawsuit if they suspect you are developing on the land. Fighting lawsuits is part of the risk.
Anyway, the person who did the presentation showed some interesting statistics. Supposedly, for every 10 acres of land that is developed in a given year, roughly 9 acres are declared undevelopable for perpetuity. That's really significant (if true).
I was moderately interested in a property in the middle of nowhere that had about 8 acres buildable (with two structures on it already) and about 220 acres of forest and a lake under a very strict conservation easement. It would have been the only property of that size and type I could even dream of affording. It was still expensive, but less than a million dollars where if that 230 acres had not been under conservation easement in the same area it'd have sold for over 10.
And it's not like indefinite means forever forever. If the next generation 4 generations from now decides these easements are not in their best interest they will be repealed. It's just a piece of paper in the end.