Terrain trasitions?

How, sorry if this is a noob question, or related in bad category. But there is quite a lot of them and non of theese seem to be exactly the right one.

I am not a newbie in 3d, but not skilled in game engines. Things are bit different in regular 3d creating.

I am unable to find out how do you make some terrain (or another large scale mesh) with not noticible textures transitions. For example. I will like to make a desert which over time change into a jungle. There will be a many midsteps between these two. It cannot be done with tiling textures. But they need to be used for level of deatil, becasue UV maping for such a large area will be ugly.

Like on this picture. I believe the ground is one mesh (not count the rocks). But there are some truck roads, some grass-like texture, sand and so on.

Any suggestions how to manage this?
Thank you very much

terrain textures use tiling, and as u can see from some of the shadows of the terrain it has been used a normal mapped terrain. In addition the truck treads are (I suppose) a mesh with a texture on it which has been placed there.