low poly terrain model: grass/trees?

i have modeled a terrain in blender because it is not possible to make terrain that looks the way i want it.
my terrain so far:

the reason i have it this way is so i can create caves and i like the simplistic art style. the terrain is a game model.

i only have minimum experience in c# but i have enough experience to wright code if given a direction to research on. so please be specific.

for one… if you could suggest a better way of achieving this art style besides placing the trees and grass one by one myself… i would greatly appreciate it.

as you can see there’s trees and grass… i want the grass to stop rendering when you are (1) a certain distance from it. (2) it is out of view. i would like the trees to do the same thing except for the distance part unless its necessary. maybe it will stop rendering only when it is out of sight and if it is a certain distance away behind you(so i will still be able to see shadows when faced away from trees behind me)

i have no clue at all where to start and if i don’t get this problem out of the way (due to performance consumption) i will not be able to continue this project. any advice at all will be greatly appreciated

You might want to take a look at the recent tutorials by Sebastian Lague at Procedural Terrain Generation - YouTube. Code is on github, see link from youtube page. These walk you through writing the code for make land formations similar to the style in your picture - no trees and grass but that is something you could probably add afterwards, using the similar ‘level of detail’ strategy used for the terrain.