I'm pretty much an expert at wireless. I know the dangers and have designed large scale outdoor mesh solutions, there are very specific reasons and laws on effective radiated power not just for interference but because of personal harm. I'm not saying it's killing tress, but when you bathe it in microwaves 24x7 it isn't unusual to think something could happen. This city could just be running their radios way too hot.
		
		
	 
 
Way too hot is an understatement.   "Bathe it in microwaves 24x7" displays quite bit of ignorance though, and plays upon people's lack of understanding of what "microwaves" are.     It's simply a range of frequencies of electromagnetic radiation.    Visible light is a range of frequencies.   Radio waves are a range of frequencies.  Infrared is a range of frequencies.   In fact, there's quite a bit of overlap between microwave frequencies and radio frequencies at the long end, and quite a bit of overlap between microwave frequencies and infrared frequencies at the other end.   i.e. the exact same radiation is called "radio waves" just as correctly as "microwaves" over a portion of the range of microwaves.   
 
And, those same trees are "bathed in" radio waves and infrared radiation 24/7.    As microwaves are non-ionizing radiation, the only other possible mechanism by which they may have any harmful effect on living tissue is by the amount of energy absorbed.  Thus, the power density is the important factor here.   As the absorbed microwaves are turned to heat, we need only be worried about where the scale is tipped - when the rate that energy gained is quicker than the rate at which it can be dissipated throughout the material and back into the air in the form of infrared radiation.  
Ionizing radiation has been understood since Einstein's days.  Microwaves and their effects on living tissue have been studied for at least 6 decades.   One study out of 10's of 1000's of studies which contradicts all the other studies is merely sensationalism.   Even the rest of the article linked to pretty much hints that it's just a bunch of hogwash.