Sorry for such a long post, but I just had a lot to say.
At some points, it almost kind of feels more like a classical RTS with a city builder twist just because of how satisfying the "sprawling out" nature of the game is kind of reminiscent of Zerg Creep or Command & Conquer. You odn't normally see this kind of restricted land usage in a City Builder, they usually just let you go full nuts with it and expect you to know where to place things. I think that also makes this game pretty accessible but with a lot of room for players to make their own decisions on the fly.
For Fynbos I don't think it's necessarily that there aren't enough trees, its the distribution can be wacky sometimes. On pretty much all the times on that last level that there were tiny inaccessible islands, there was at least a tree on one of them that could have been on the mainland. Sometimes, trees will also get a bit clustered instead of spread out across the map. Those tend to be the biggest problems, and a few times it made one or two whole corners of that map completely inaccessible normally without tricky and clever timing with arboretums.
You could literally only have like, 4, or 5, trees on the entire map and as long as they are all in the right positions that's more then enough. That could also provide another way people could make a different kind of pleasant-looking reclaimed wastelands, by having a thin stretch of forest that goes everywhere instead of one big cluster.