I get something like that with my HD7870. Trees at medium near distances have random pure white stationary pixels in them. If you slightly change the view, by turning a turret for example, the white pixels jump all over the place and the tree shimmers. I tried different settings and I think this is what I found: with Post Lighting and AH AA on the white pixels went away, but I normally run with Post Lighting off and I don't like the AH AA anyway. With Post Lighting off and the graphics card set for MSAA I get the white dots. With the graphics card set for adaptive MSAA the dots go away (but the frame rate drops). With the graphics card AA turned off I think the white dots went away, but then you get aliasing (which I personally hate with a passion). I have Tree Detail at about 18% (i.e. just at the trailing "l" in "Low Detail"). Note I have only seen this with the latest patch.
Edit: the shimmering I see (which may be different from that the OP sees) is most obvious at dawn and dusk and occurs only on certain trees or even parts of trees, like the vines on the Banyon.