N = 1, but looking on Google Maps, pretty much all major parking lots around my suburb have at least 2 (small) trees per 20 parking spaces. In most large lots, the trees occupy their own islands, but a few lots have a line of trees around the perimeter instead. IIRC, there's a county rule requiring a certain number of trees on a property relative to the land area. An least in some properties, the issue has arisen of developers placing trees too close to buildings and other structures for their size.
I rarely see significant use of trees around my home. It's unsurprising that cities mandate them because they provide shade... so if PV arrays confer even more shade, you could stop relying on trees!
With a mandate to build a parking lot of a certain size, a business is going to say no trees; they would reduce auto capacity, present a maintenance burden, attract wildlife, and continually drop organic stuff on your customers' cars. And so that's exactly why cities find the need to mandate them!
