It seems that, while player in park building mode, a bug causes the game to show impact on nature in area where it intersects with the park effect instead of showing just the park effect.
On screenshots you can see:
- Influence shown in building mode.
- Actual park effect area after park was built.
- Areas of nature, including made by trees around, after park was built.
UPD: Solved in beta release 1.12.42 ❤️