Improve render time for Grass/ Forest? (Eevee)

Question

Is there any way to improve the render time, when you have grass and a forest? Because i make animations, i have now a problem. With only one tree and without grass, the render time pro frame are about 30 to 40 seconds. But now with a forest and grass, i take the computer 2mins. This means, the pc need around 14 hours for 28 seconds of animation with the camera. There are no animals or anything else yet.

Is there a way to say Blender should only render 1 to 3 trees and copy the information of this to every other tree and grass?

Answer 1

That what you refer to with

copy the information of this to every other tree

is called "instancing". If you use a particle system or arrays to distribute your trees and grass, you are already making implicit use of instancing. If you however use manually placed copies for your trees, you might want to use the option "duplicate linked" (Shortcut: Alt+D), to keep the scene more efficient to store and to render.

Also, generated trees tend to have a LOT of polygons, most of which do not really contribute to the perceived detail (especially if the trees are in the background!). So it may pay off to use the "decimate" modifier quite drastically on background trees.