The tree blowing in the wind will introduce its own amplitude (brightness) fluctuations. It will be hard for you to tell which amplitude changes are signal from the source and which are noise from the tree.
Edit: Looks like you answered yourself while I typed that, where you added:
> Couldn't this be dealt with if you know the details of the tree's dimming ability?
If the tree is moving, and you’re far enough away to resolve individual leaves (which is not unreasonable) then its “dimming ability” is constantly changing.
The tree blowing in the wind will introduce its own amplitude (brightness) fluctuations. It will be hard for you to tell which amplitude changes are signal from the source and which are noise from the tree.
Edit: Looks like you answered yourself while I typed that, where you added:
> Couldn't this be dealt with if you know the details of the tree's dimming ability?
If the tree is moving, and you’re far enough away to resolve individual leaves (which is not unreasonable) then its “dimming ability” is constantly changing.