That will be difficult because of the scene size, but I will try.
I´ve noticed another important thing. It happens only one time after opening the scene and directly rendering it. If you abort and click render again, it works perfectly, but with network rendering this is still a big problem. Seems it doesn´t update the surface before rendering the scene at least one time. Because directly after opening the scene the trees are not shown in the viewport, but they appear after rendering.