To ensure not all the cases presented are ones which resulted in tree removal I have included one I managed to save. A mature Horse Chestnut (Aesculus hippocastanum) situated at the Yorkshire Dales National Park Authority head office car park in Grassington; situated by a picnic area, an access gate and overhangs frequently used parking areas.
There had been pressure on this tree due to:-
- Park staff believing (based on an earlier diagnosis) the tree to being infected with
Pseudomonas syringae pv aesculi (Bleeding Canker of Horse Chestnut). - Concerns over a historic non-occluded wound (c.45cm ⌀) on the south side of the tree in close proximity to the branch union of a large diameter, low overhanging branch over the parking area on the west side.
- Interference with parking – a great deal of the canopy overhangs six car parking spaces and the low hanging branches obstruct parking. There is also pressure on the trees due to a need to create additional parking.
The tree was inspected in summer 2018 and I felt the tree was an excellent specimen with considerable amenity value. I did not agree with suggestions of removing the perceived hazard – the overhanging limb as this would create a further large wound on an old tree and considerably impact on its aesthetic qualities. If the tree did have structural weakness due to the defect and/or Bleeding Canker, full removal to facilitate additional parking would have been heavy handed.
The symptoms of Bleeding Canker are stem bleeding and cankerous lesions which can become a problem when they girdle the stem and branches. This leads to bark delamination and branch drop as the wood dries out or becomes infected by secondary diseases. Following inspection, I found no show signs of ill health; bark morphology appeared typical for a Horse Chestnut this age and the weeping apparent on some of the limbs was bacterial wetwood. The symptoms of canker have been had abated. Indeed, evidence suggests in some infected trees, development of the disease can be slow and some trees can show signs of recovery (i.e. vigorous callus development around cankerous zones) (Webber, 2018)
There was some softening around the perimeter of the wound, and probing found some decay although the morphology of the branch / stem did not indicate any weighting issues nor was presence of decay fungus evident.
At around the same time there was early planning around redesign and development of the outside land. Given the tree’s high amenity value, multiple targets and pressure from car parking, although I didn’t feel the tree posed an immediate hazard, I took this an an opportunity to suggest a long term management plan for the tree which included fencing the canopy and making more of feature of the tree. This was my mistake (the outcome being more pressure for additional parking and removing a tree ‘with problems’). I commissioned more detailed diagnostic investigations which had the purpose of providing management with greater evidence that the limb was sound.
Testing with the Resistograph was carried out in four areas around the branch union and the results confirmed that the softening at the wound surface was superficial. It showed no internal decay and the branch connection to be sound therefore suggesting little chance of branch failure at the present time. This result in effect, in backing up the basic tree assessment, took the pressure and focus off the tree giving park managers the reassurance they needed.
Further recommendations for the tree will be to continue monitoring it annually for any change/ presence of fungus and we will consider retesting the branch union again with the resistograph if any symptoms become apparent. A further recommendation was to trim back tertiary growth to reduce interference from overhanging branches.
Tree Risk Management Portfolio - M140849 