Realtime shadows of trees cause MASSIVE fps drop

Hi!
I just started messing around with unity; I don’t have any experience in it so i’m sorry if this is something stupid i ask.
My problem is that placed trees cause a massive fps drop even with a low shadow distance. I would like to keep the realtime if it’s possible because i like how they move as so do the leaves and also i want to make my game have day and nighttime. I think it’s not really possible with static shadows. Can anyone help me how can i tweak this? Other alternative solutions maybe? I’m open to anything.
Also here’s a pic:

Even this makes my ‘game’ run with 15-20 or even lower framerates.
(I have and AMD FX-6100, a HD7870 and 12gb of RAM)

Unity’s terrain system and everything associated with it is dated and bad. Start somewhere else.

And what can i do with that then?