I actually did produce a street tree list for the City, breaking it down into size appropriate trees; i.e., for 4 -6' tree islands, 6-8' tree islands, over 8' tree islands. I kept away from trees that require space for a low, spreading canopy as it drives me nuts to see a tree constantly trimmed against its natural growth pattern. I also tried to keep in mind the highly dense, low skirted trees. These, in my mind are also not suitable for street trees as they can block visibility for clear view triangles, producing blind spots.
In my mind it is all too easy to remove a tree and plant another. And whereas that is necessary at times, it is also necessary to remember that a tree doesn't become a carbon sink for 10 years and will not be producing its maximum benefit to the environment until approximately 25. So if you are removing a tree for the sole reason of expedience then you are possibly losing a lot of the very attributes and benefits for which we have trees.
Also, in a City situation where you are determining what is in everyone's best interests, you need to consider are you taking down a mature tree that is providing shade in the summer and therefore cutting electric costs on air conditioning for that resident? or maybe that is the only means of air conditioning that person has? are you taking down a portion of the shelter belt from winds, or buffer from traffic, are you taking down an element of that person's property that is adding substantial value? These are all factors you need to look at. When that tree is on private property you also need to consider the public relations factor of diplomacy in handling a potentially volatile situation.
Our tree ordinance does have a clause that states the City can require a home owner to remove a tree if deemed hazardous. (Or mitigate the situation in some manner to remove the hazard.) But they have no one on staff that knows anything about trees whose duty it is to maintain and manage the city trees.
Our little city doesn't have the budget at this time for a City Arborist (or at least they don't have the desire to budget this in). OTG, I can only imagine the difficulties you run into in your large city. My hat is off to you for handling a department that has to satisfy so many diverse thoughts and needs.
Again, I applaud the PW Director for trying to look at all options. I will say, my very first question to him was "Have you spoken with the homeowner?" I wouldn't think it wise to put a lot of time and expense into making special variances for a tree that the homeowner might be considering removing anyway. So that would be my first step...talk to the homeowner.
Sylvia