Thank you for your help.
i hope youre not getting too much snow, be careful.
The point light dont need to be in influence range of any foliage to get the FPS drop, i only need to be near to the point light with dynamic shadows enabled and the landscape with the foliage needs to be in the map.
If i delete the landscape or only the foliage i can place really many point lights without a big performance impact.
The other way to get more FPS is to disable the shadows.