@Joga, nice Model so far.
But you've wasted too much polygons in my opinion.
Ive made a very basic and simple example to show you how to reduce some polygons... Dont get the details like your one but if i add the "details" to this Model, the polycount shouldn't be over 700 - 800 (Just the half of your count).

heres my "example" (fast and ugly grin / 368 polys so far)

regards Sebastian

[Blender]Terrain creation ENG/GER
[Blender]Low Poly Tree Modeling
[GIMP]Create a Texture for Terrains