When I was working on Street Trees in London our general practise was to
continue the method of pruning that had previously been employed on the
particular tree.It soon became apparent that many trees had been planted in the
wrong place, and they had therefore to be severly pruned to keep within bounds
of their surroundings. Most of the large trees were either Planes or Limes and
although in many cases they had matured into large trunk sizes their tops were
kept small by many years of hard pruning or pollarding, what struck me however,
was that even after all the years of severe prunning the trees were in fairly
robust health with no real sign of rot. I can only attribute this to the fact
that both trees have many medulury rays which can act like a wall and facillitate heavily in
compartmentalisation of the wood. Which fitted in neatly with the traditional
ancient use of Limes in Neolithic and Iron age Britain.
Most Prunus cerasifera trees I worked on had Phellinus pomaceus (plum heartrot) fungi infestations to some degree, although the trees seemed to be surviving with this form of localised rot. Prunus avium and Prunus 'kanzan' (Pink Cherry) generally had various cankers eating away at them and did not survive long. The Maples (Silver) stood up to heavy prunning very well without any top rots developing, but because of their thin bark were constantly losing bark low down on the butt and developing rots, making them unsafe and prone to butt rot.The Aesculus (conker) trees I worked on usually had bacterial wetwood but otherwise they seemed healthy and living to mature sizes.Although we did have four that got blown over during some high winds over christmas 1997, all of them had rotted roots with much of the buttress roots soggy and crumberly, here you can see a buttress root that i cut out and photographed, as the trunks were sound i took some slices to make into small garden tables, these came from an aesculus that fell over on clapham common onto the pavement and road.
Most of the smaller trees planted as street shade trees did not stand up very well to the typical treatment meted out to them, i.e. people allowing their dogs to use them as personal lavatories and depending on the frequency of use would soon start to suffer from Urine poisoning (high Nitrogen,which encourages poor soil fauna). Also bark damage done by cars, pedestrians, etc. Although some ornamental Apple trees (Malus) seem upon first observation to be coping better with life in the street better than the Rowan(Sorbus), Whitebeam (Sorbus) and Prunus species, when it comes to street abuse all thin barked trees soon succomb to ill treatment. Robinias (Psuedocacias) with their coarse thick bark seemed to be able to take a lot of punishment without dying, but the tree top didn't take too kindly to pollution and usually seemed to have twig die back as a common fault even if the tree itself seemed in good health.