yesterday, I was on a rather small notebook lcd and could not see any noise. However, now that I am viewing this on a larger screen, I understand and agree to the observation. It's not atmospheric noise, though. These plant models have very frail twigs and narrow needles, and with the resolution rendered, they appear altogether like a noisy mass.
I've rendered a crop at 2400 width, and left the crop unaltered (no postwork). There you can see that the "noise" is slowly resolving, but not gone yet. Maybe at twice the size again, the image will have enough pixel space to actually display all the fine details in that area of the image.
Regards;
Frank