Alright. Let's do this.
czzzz - Forest Warden
I think the +2 Cards makes this better than Shepherd's +1 Action, but that's not too much of a concern because this doesn't come with a Pasture. The on-gain effect is a pretty good way to incorporate National Parks. The card itself doesn't mind excess greening (which you'd want from National Parks as they're quadratic) but the Gold trashing is still a good cost for a National Park. Good entry!
bryguy - Treemonger
My first thought was that this was a bit weak, but getting six Provinces and three Curses from six plays of this if uncontested... pretty solid. I like the game of constantly stealing National Parks from your opponents and cursing them for doing so, but this feels a bit... swingy. Blame the mechanic itself for that, not your submission.
Erick648 - Forest Paths/Tycoon
...Night Cellar and a weird Rabble/Golem lovechild. Both cards in here just feel... too weak, and while the double junking on gain seems intended to remedy that, I just don't see myself doing anything but eating the National Parks myself... which is not really what you want when both of you will always get the same number of VP from them. Tycoon's similarly weak, not really synergizing/antisynergizing with National Parks in a meaningful way and likely to have the Golem problem of being worse than Laboratory (except on 3-4 player boards, where the Pirate Ship stacking problem is invoked hard and fast). Good ideas? Yes. Needed a bit more time in the oven though.
exfret - Mountain Goat
A solid card that gives you a reason to keep your Estates around, or even buy more maybe? That'll be board dependent. Really good answer for junking attacks (you like Goat, you like this, though getting it a bit later than Goat isn't the best) and has some nice interactions with National Parks. Is the 6VP split (assuming you Goat your Estates and your opponent keeps them) worth you keeping the three extra stop cards? Who knows. Either way, some good interactions on display here.
emtzalex - Conservationist/Survey
Embassy's already pretty weak. Having to have no National Parks within two hands' worth of cards, plus give up a $6 buy (or Gold gain if you can cheat one out)? It's a buff, granted, but by how much? There's more kingdoms where you can do interesting things with this than Embassy (Exile kingdoms notably come to mind) but does that make this worth buying on the kingdoms those don't exist in? The opponent junking with NPs is nice, but I don't think it saves this.
Xen3k - Industrialist
The more I look at this card, the more genius each design decision becomes. Probably a bit quicker to mass-buy Industrialists and then trash them for Provinces than Big Money, but should be slow overall. The self-junking is a good restriction (and the "doesn't share a type" restriction makes it so that you can't trash your NPs for Provinces) and I think this plays a more major role on most boards than Expand does. As opposed to Expand's Remodel+, this feels like a card solidly designed to be your source of alt-VP while getting you a couple Provinces in the meantime, and it does a really good job at that. Nice work!
--------
Honorable mentions: Forest Warden, Treemonger
Runner-Up - Mountain Goat
Winner: Industrialist
Congrats to all entrants!