vegetation requires max. a few thousands particles, so you have enough for rain and snow, and for some other special effects. but it is only one option, alternatively, if the vegetation is not destructible, a lightmap can be generated, but it needs time and a large texture.

these are the 2 solutions for free/extra, you have pssm shadows in commercial or above, what can be also used with good performance if everything designed and set correctly (I "hacked" shadows.c a bit for better fps, what I'll include in the script package after a few weeks of my editor update, but it will require an engine fix to really work as I want)

Free world editor for 3D Gamestudio: MapBuilder Editor