If i remember correctly the first number is teh quantity of trees and the second is the distance that you can see trees.
trees = {1000, 15000}; = {quantity, Distance}
So you maybe better off if you want more trees do it more like this
trees = {1500, 9000}; more trees but a tight less at the distance.
The second value i think it's in km .
I don't know if BS accept a higher quantity tree value..
But i can completely be wrong.. also I don't know if BS now read well the Graphic.cfg