Actually, I like the trees, but, first, have you ever visited the Gunship Helipad ? It has lots of Gunship! mods. The only tree mod I know of is one that substitutes palm trees for the originals, in a new desert terrain, and I think also a mod that substitutes snow covered trees. Those are availabe when you install Mod M8 . What I've done before, when I want to change the trees, is copy the trebun.pca and trebun.pcb from the mods\ter_des to the data\textures folder, and then I have palm trees in a European terrain, lol. Trebun.pca and .pcb are all you need to change to get the palm trees, if I recall.
On the Helipad site mentioned previously, are instructions to mod all the objects in the game, so feel free to create new trees. I also have a site with more Gunship! utilities, tips, and skins. It's in my signature.