*warning in this post some of the numbers I quote will be rough approximations, I am not going to take the effort to find the exact numbers for this discussion*
Here when land is in "Tree-growth" the tax assessed value of the land is set at a very low amount [for example $100 per acre for hardwoods, $150 per acre for softwoods, etc].
So the annual tax bill [the mil-rate times your assessed land value] will come out to being maybe $1 per acre. [ours has actually been around $1.05 per acre]
Whereas, if they had taxed it at the purchase price of the land, $300 per acre to $1,000 per acre, then your tax bill would be between $3 and $10 per acre.
If you own 100 acres; under 'treegrowth' you pay $100 property taxes. Without 'Treegrowth' you could pay from $300 to $1,000 annual property taxes [assuming they assessed the land at the purchase price].
I just took one acre of my forest out from the 'treegrowth' plan. To account for my driveway, house, barn and garden. My property as a whole is riverfrontage. And in some areas of the county, riverfrontage land has a market value up in the $80,000 - $90,000 per acre range. So the tax assessor set the assessed value of this one acre [which in itself has no river access] at somewhere around $86,000. I only bought it two years ago for $900 per acre. But this is the new assessed value. So we just got a new tax bill. Just for this one acre of non-treegrowth land: $860.
So next year my property taxes will be $860 [for the land under my house and barn] + $46 for 41 acres of surrounding forest: $906.
I see the 'Treegrowth' idea as a value, to encourage folks to keep land in forest.
Around here you can still do pretty much anything you want to do with the land, so long as it still grows trees. Obviously clearing an area for a house foundation, is going to limit the trees that grow right there. But you can drag in a one-room cabin on a sled, and not interfere with the 'treegrowth' concept.