Thank you, no… there is no speedtree involved 
the trees are assets from the 3dmotive tutorial and the grass is a “never-ending back and forth”… now its a mix with different technics… mix betwen fully polygonal blades for near and one sided for far distances. I saw a document about real time grass and tryed some parts from it http://www.kevinboulanger.net/grass.html a great document!
Hey… i tryed lightmass on 4k too but had a lot crashes. Since then i’m on dynamic gi and i love it so far. I think you should follow this link to set your lightning up https://wiki.unrealengine.com/Light_Propagation_Volumes_GI
And DFAO is distance field ambient occlusion https://docs.unrealengine.com/latest/INT/Engine/Rendering/LightingAndShadows/DistanceFieldAmbientOcclusion/index.html