Hello Martin!
Thank you for your comment! Yes I have swithed from GPU and I am currently trying to render with CPU, but Oh My God its slow 🙂
But, it works! So a little patience and it will get through. But I will also try this at home with my home computer. It has 8Gbt of VRAM so it should at least be enough for render. I will try to adjust the tree´s dense geometry, and make it less dense. I think the subdivision is quite high, so I will try to lower the resolution.
Because when I add the trees, the RAM usage goes up. But as you said, there are certainly many more tweeks I can make.