Hi I am currently modeling a hi-poly terrain in mudbox and I wanted to know, do I also need a second UV Map Channel when I import the mesh into UE4?
When you just use dynamic lightning then you dont need a 2nd uv channel, otherwise you should create one
Ok, just to be clear is it only, static meshes that needs second uv maps? for example non moving meshes?
Nope, here it just depends on the lights. When all lights are static, so they dont move, then you should rebuild the light -> so you will also need a 2nd uv channel. But when you for example create a map which has a day & night cycle, lights that get turned on/off,… then you wont need to rebuild the map -> so you dont need a 2nd uv channel
Ah ok I see, I understand now! thanks for the tips, man next gen lighting can get quite complicated lol.
Actually, it’s not that next gen… was there for UE3/UDK all the time.
There are exactly two ways, and depending on what you want to do one is good and one is bad.
Static - your level lighting looks the same all the time? It wont change? Then use 2nd UV channel and bake lighting. Higher quality & better performance.
Dynamic - your light changes? Day cycles, all the lights go on and off or whatever? You can’t bake that. Forget about the 2nd UV channel.
Instead of that you might have to invest time into optimizing performance…
Don’t import it as high poly, it’ll freeze the engine if it’s over 2 million poly’s!
You need to create a low res mesh based on the high poly one, (with normal and AO baked in) 
I´v´e imported some 3-4 million poly´s terrains, but what kills the framerate is trees 
Even if use height-maps the vegetation is a challenge, and ground plants like grass perhaps the most difficult in large scenarios.
This scene has 45 000 trees, and it went from 70+ fps to 30-50 even if not many in sight, I only have 1 LOD so that might be the reason though.
://s28.postimg.org/jjdac8uvt/test4.jpg
Why dont you just use culling for small plants like grass? Then your framerate will be much better. 
And I would also recommend you to use 3 LOD stages and trees that just have around 1000-1700 verts.
Thanks, I´ll test it out, when I figured out a proper biomes distribution, and made some more low poly plants.
I think I somewhere read that UE4 is able to [generate or load?] Billboards for last LOD…
Would be very interesting in order to bring vegetation up to speed.
Do you or someone else know about this?
Try playing a game on a PC that NASA didn’t invent with 3-4 million poly terrain, it’s complete madness when you could have captured almost all that detail in your textures with a ten thousand poly terrain.