Ready for the Foliage tool
Each asset comes as a static mesh with LOD0–LOD3, materials for bark and leaves and collision. Paint it with the Foliage tool or scatter it with PCG.
Unreal package or plain files
Download the Unreal package with meshes and materials already connected, or take FBX or GLB and import it yourself with Interchange.
Performance
Triangle budgets per LOD and a two-triangle impostor for the far distance keep large forests cheap. Low-poly assets use vertex colour and no textures.
Variety without extra work
Export several seeds of one species and paint them together: the forest looks natural instead of tiled.