Reality Factory

If i put many trees on a terrain,each tree to have one staticmesh for the bark and one for the leaves for setting the canopy as double sided z sorted visibility check etc,
Will that take up much memory,and it would be better to export the trees as groups with their lod?
This way some of the front trees of each group might show Lod level of less detail earlier than they would but it will be faster rendering-will it?

Something in between,which is trees exported in small groups with lod might be better for having less entities in a level.
Just these trees are for a specific terrain and location.