How to reduce draw calls on dynamic trees?

Here is my camera and terrain settings: Camera-->

Near clip: 0.3 Far Clip: 800


3000x3000 Resolution Pixel Error: 200 Detail Distance: 20 Detail Density: 1 Tree Distance: 500 Billboard Start: 300 Fade Length: 5 Max Mesh Trees: 200

In this situation my draw calls are about 1.9k, and i tried to off everything, no big change but when i disable trees suddenly it drops to 290 draw calls. What is the best way to have trees without so much of performance sacrifice? Thanks a lot.

Make billboard start distance much lower, because in billboard mode a bunch of trees are drawn as single drawcall; in tree-mode each tree is rendered separately.