Foliage + Lightmaps is broken/bugged/dysfunctional - Detailed explanation

General Feedback & Requests
2

You would probably be waaaaaay better off using things like DFAO and cascaded shadow maps or a combination of the two; than trying to lightmap 31k trees.

https://docs.unrealengine.com/latest/INT/Engine/Rendering/LightingAndShadows/DistanceFieldAmbientOcclusion/

https://docs.unrealengine.com/latest/INT/Platforms/Mobile/Lighting/HowTo/CascadedShadow/