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).
Mega-corps building cookie cutter subdivisions or commercial space obviously pay less because they're vertically integrated and highly streamlined.
Some small scale 1-4 unit stuff (single structure here and there) is exempted, unless it's too close to water of course.