Texture filtering only smoothes bitmaps. Texture Anti aliasing smoothes procedural materials, like the barks of those trees. If you set Tex Filtering to 100% it will smooth 100% all texture maps in the scene, but not the tree barks (this was just to be precise). Now, what is strange that one of the conifers flickers, and not the other, I looked at their materials, and they use the same material, so I'm lost! If the Bulky doesn't  flicker, then copy/paste it's material onto the Cone shaped and see if the flicker is gone.