That's the trick. I'd think about toning down that texture a little, but that's purely a matter of taste and would be a call you'd probably want to make after the whole map had been done.
I'd suggest possibly making your clouds a little more turbulent at small scales so that the varying light/shade on the canopy is a little more suggestive of small trees. Possibly another layer of clouds over the top of your current one with the turbulence turned right up but with low opacity. Rob mentioned a better filter than the standard gimp one, which might be worth it as the standard one is a bit gridded.