I think the problem with the trees is that they are photorealistic, where the rest of the map they are on is inked, and therefore not photorealistic.

I've have lots of problems mixing styles over the last couple of years, so I know how difficult it is to get this kind of thing to work.

If you add drop shadows to the trees they will look a lot better as trees.... but if you do that there will be a much greater mismatch between the trees and the buildings that are inked and definitely not photorealistic.

Difficult to know what to suggest in the time available...

If I had to chose between the trees and the rest of the map, I'd chose the rest of the map and try to ink the trees to go better with it - but that really is my personal approach, and one that would make me go pale at the thought of all the work I would need to do to make it so, in the time available.