Four trees planted last year died on Acorn Street, and were replaced today. From the soil removed (almost entirely clay), it is clear that the trees probably died because the holes were not properly prepared for the trees. To be properly planted, the hole should have loam under and around the tree; otherwise, it is more likely that the sidewalk will be pushed up by the roots. Also, it is not clear that the roots were loosened when removed from the container, so as to ensure proper growth; if not, the tree is less likely to survive, like the trees which died last year. Something should be done to prepare the holes differently from last year.
FYI:
https://www.nycgovparks.org/pagefiles/53/Tree-Planting-Standards.pdf http://www.milliontreesnyc.org/html/plant/street.shtml
http://www.cityofboston.gov/Parks/StreetTrees/seasonal.asp
http://ci.richland-center.wi.us/parks-rec/forestry/