The polygons currently have no way to set the biome of the vegetation.
Hi,
For the moment, we don’t plan to add the biome option into the polygons. As these airports are part of the base game, we will let the game define the biome.
Cheers
Nicolas
Adding my vote to this. I spent a lot of time picking a biome to get scrub grass that looked right for one of my airport updates and the results were totally worth it. Would be very sad to not be able to have that via World Hub.