I originally attached my trees to my terrain editor which allowed easy distribution and dynamic live shadows. The problem with this was that i wanted lots of trees for my forest and it created problematic laggy frame rate issues when playing from the beginning where you see most of the trees in the distance. The shadows from the leaves were brilliant but another problem that came up was that the trees were not affected by global illumination. So where the sun was shining, you could see the tree texture but when you looked behind it, it became pitch black. That isn't true to real life especially when my scene isn't night time but quite bright and warm. Light should be bouncing and creating a darker shade to the non lit side of the trees.
The only way i could do that was to take the trees off the terrain editor and place them all in manually which seemed to do the trick. It was major time consuming ball-ache but it made the scene look much better and more natural with better lighting. The shadows became still but it removed the lag. For this busy scene its best not to have the dynamic live shadows. I quickly placed trees into the level by selecting the asset in the package, holding alt and S on the keyboard then left clicking into the area in editor to place it down nicely. I still had to manually re adjust the the rotation, scale and tilt of each tree which took time but it was all worth it in the end for the final product.
Since the last trees, i added more leaves and stretched them out and down a bit to get more bend. After reimporting the ASE file, the whole scene transformed and become more drastically filled, and less sparse. That was all it needed to now look like a deeper more immersive and slightly claustrophobic and mysterious forest. Compare it to one of my older posts where the tree leaves were more empty and very plain and straight and you will notice the difference.