1. `natural=` doesn't mean it's "natural". It means it's water, vegetataion, rock, or earth. 
2. I'm not opposed to adding its functionality, but trees can be planted elsewhere for noise and wind as well. If it's inside a housing estate for noise, it's already `=urban`. If around farm fields for wind (windbreaks), it may be `=agricultural` (it's not clear what "agricultural use" means). I have tried using `insulation=soundproof` https://wiki.openstreetmap.org/wiki/Proposal:Insulation_proposal for this elsewhere.  