How to implement a dense jungle (with performance in mind)

I'm thinking about how to make a dense jungle scene (or scenes) that won't completely crush people's computers. My target platform is for medium to high-end PC users. I'm kind of looking for tree and grass techniques that perform well, because in all of my testing, it seems to be the trees themselves that cause the most performance hit.

I'm using SpeedTree trees, but that's not a requirement. I'd switch to something else if it looked somewhat ok and performed well. Anti-aliasing seems to be the biggest culprit in terms of performance (with trees) as well. If I have thousands of trees on a terrain, and I have anti-aliasing on, it's pretty much good-by fps. Even using the post-process image effect anti-aliasing (temporal or other). If I completely turn off anti-aliasing (i.e. don't use any at all), then I can kind of get decent fps (still usually under 60 fps though). But not using anti-aliasing makes the scene a lot worse looking of course.

Perhaps there's a way to "stream" in trees/grass around the players location as they move? Of course there is tree instancing, and perhaps some other techniques?

Just kind of wanted to "spit-ball" here and see maybe what other people would do (or have done) in order to make a scene that requires lots of trees/grass.

 

The cool thing with dense is that it generally mean a lot of visual blocker, so my first question how do you envision it ideally in the best case, do you have concept art, and secondly is what is the gameplay requirement, for example can the player climb to the canopy, fly above? is restricted to floor level?