The survival chances of an urban guerilla tree are poor.  The main threats are lawn-mowers, removal by non-tree enthusiasts, removal and replacement with something smaller by council (Council love those low growing grivilleas...nice flowers.... but zero shade qualities). Trees get hacked, pulled out and discarded by baked and concrete jungle enthusiasts, sawn off at the trunk, ring-barked.  Sometimes they are poisoned and very occasionally they die of drought.

The main cause of death is human intervention.  

If we are to survive on a rapidly heating planet...we need a different approach to trees and growing food and vegetation in the city.  

On a practical note the areas of the Upfield Urban forest that are doing best are those covered in tree-growth and vegetation and where flowers outgrow the weeds.  It looks like working intensively on small pockets has the highest chances of success.  Well done foresters.  Please get involved...everyone!