We are undertaking efforts to get the city to provide tree guards for the remaining tree beds on our block that do not have them. But in the meantime, residents are able to have one installed through a donation program run by the New York Tree Trust. You basically look through the styles they offer, and sizes then make the requested donation, and they will handle everything. It seems that this is cheaper than privately going elsewhere to have this work done, and certainly quicker than waiting for the city to approve the expense.
You can read more about the plan here: http://stewardship.nycparks.org/library/tree_guard.php
And here is a list of the treeguards they offer, and the prices: http://www.milliontreesnyc.org/downloads/pdf/tree_guard_donation_table_2014.pdf
Thanks to Randall for bringing this info to the block association’s attention!