You know where you turned off the open gl? Go back there. Turn down the line detail of the meshes. You need to on a big project like this. "But I want all the trees to look the same.." Huh? So you drop a tree into your project and render only( render only selected objects) it with alpha channel and plunk it onto a alpha plane. I bet it will look the same. Render about 20 different trees this way. Make crosses with two planes so the shadows are correct. got to be exactly 90 degrees and also has to be that way to the camera. Plant in the distance. Save . Plant real meshes. Render.