It takes forever to export Forest Pack to udatasmith file

HELLO!
When the coverage of Forest is small, there is no problem in exporting.There are 6,251 trees, the export speed is acceptable.

But when the coverage of Forest is big, it takes much longer time.When there is 263,332 trees, it still did not finish exporting even after 10 hours.

Then I reduce the trees number to 3,000, and it took 6 hours for exporting.

253363-5.png

BUT, the problem is, if there is only 3,000 trees, it is not enough for the surrounding environmenta. And it consumes too much time. If I need 300,000 tress, since I never try it, I have no idea how long it would take, but I guess it will be extremely long. My client and I do not have such time to wait for it.

Thereupon, I consider to plant trees in UE4. After all, Foliage is equipped in UE4, and it is much quicker to generate great amount of trees. But, I come across new difficulties.

Please forgive my verboseness. I need to explain how I plant trees by using Forest in 3dsmax

1.assign on which mesh surface the trees generate

2.use mesh in the scene to limit area the Foliage generates, which are the area that surrounding building located.
3.use Spline to limit area Foliage generates, thus it can avoid intensive botany and reduces amount of plants

Through above mentioned simple procedures, the result can satisfy my demand----surroundings no need to be delicate, but can not be wrong

However, when I generate plants in UE4, because the surroundings can not be too small, to generate plants in such big area and meanwhile limit the area that plants can not be generated (eg. Road, buildings, pavement), it requires such job to be finished in short time since surroundings are foil. Considering my current understanding and grasp of UE4, it is a difficult job to me and I need your advice and guidance.

Below is whole scene of a project.

253364-6.png

In many occasions, the camera is focusing on the main buildings. While the surroundings (not important but can not be wrong) are located in a certain distance away from the main buildings.