That does seem like a surprising amount of noise for AA12. The first thing I would try is turning off Soft Shadows to see how much that is contributing to the issue. If you still get a lot of noise, then perhaps your foliage textures are very hard to antialias. I note that it appears to be an issue not only in the trees but also the grass, which is interesting. What are you using for grass models? You could then try Max Samples at AA12 just to see if it's a noise threshold or other adaptivity issue. If that is still too noisy, that supports the theory that there is something particularly hard to antialias about your plant textures or models. You might then take a look at the textures, make sure the alphas/opacity are working properly, and make sure there is not an excess of high frequency noise or other detail in the plant textures.
As with all problems of this sort we can provide the best support and advice if we can see the actual file. But I know that is seldom possible. If you can share any additional info or scene data, you can send it to the support address.
- Oshyan