Every time i start a game the forests and jungles are " below" the terrain so that only the tops of the trees are showing.
This problem only applies to the forests when it is on a hill

what can i do?

The fault is at your graphics card. It is probably too old to show the trees on hills as they should. My former graphics card, a 32 meg Nvidia Gforce4 had the same issue.

This thread lack of a better place to be discussed IMO.