Check your references but also remember that not everything was photographed. Just 'cuz you don't see it in a photo doesn't mean that it never existed.
The use of wooden planks was a common practice, but I suspect that this was subject to the availability of said planks and/or the raw materials to make them. As regards to the terrain, to reiterate what's been said, it depends upon the time of year and the locale. The Russian Front was a BIG piece of real estate and there were many types of soil and vegetation present in different areas. Also, often times Luftwaffe units were forced to move to different airfields on a sometimes daily basis. So the groundwork is really up to you.
My advice is this: If you'd like to use the planks, use them. If you want to put in alotta grass, go for it. And if you want to add snow, don't ask me to shovel it!
(I hail from Buffalo, NY and snow is a sore subject!)
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