Local Oak
A boundary oak by a country lane, well used by cyclists, targets include power and phone lines.I became concerned with the health of this tree primarily because by waste system follows into the ditch behind the tree, a problem with the treatment system? However this had not impacted an adjacent tree that is closer to the exit of the treatment system, in fact this Oak was in great health
Oak investigations
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Diagnosis
A large section of the tree on the side by the road (North) died back quickly, I sought permission mirco-drill. I drilled the tree at 0.25m, 0.5 and 0.75 from ground level and some buttress roots. Each reading showed significant resistance as would be expected in a healthy tree. I had expected to find a butt root fungi at work, I examined further up the canopy and other than common defeats with a tree of this age, I found very little to explain the rate of decline in the tree. Interestingly the south side of the tree remained in a healthly condition.
I visually scanned the tree again, ivy had been severed. A closer look, I discovered the bark had been cut into, the cut was approximate 23cm deep and 86cm long.
I suggest that the tree has effectively been ring barked across 45% of its circumference and the decline in its health can be explained by the damage to the phloem. An intact vascular cambium may be able to repair the wound, here it is too excessive. The damage is preventing sugars being transported between sources and sinks (users) on either side of the injury, the injury prevents the transportation of sugars moving from the crown to the roots leading to dieback from carbon starvation once the existing reserves are exhausted. (Hirons,2016,263) Due to the depth of the damage, the tree was not able to respond effectively by modifying parenchyma cells by suberisation and lignification of their cell walls (metacuisation) (319) The damage done has exposed the sapwood to desiccation and embolism thus limiting the hydraulic function of the damaged xylem. Works by Boddy & Rayner (1983) explained the role of moisture content in the concept of tree decay; moisture being a passive form of defence utilised by the tree. I expected to see a heart rotting latent decay take hold. Here a white rot was found. (SEE APPENDIX)
Prognosis
The tree is a mature oak, in the stems of such trees, the columns are confined to discrete axial strips that are separated by intervening dead strips. In the event of “pruning” severing the tree, it could die along its entire length unless it lateral connections to other columns remain partly functional. (Lonsdale,2013,188) SEE APPENDIX
It can be witnessed that at the first main union in the stem, the tree separates into two functional units. Die-back in the stem that heads towards the road and that the secondary stem is in good vigour. Lonsdale explains this occurance “ individual branches and roots of a tree have a certain degree of autonomy, owing to partial separation between there pathways of water conduction” (2013,195)
The prognosis remains positive, the tree has effectively retrenched. The deadwood that overhung the road and utilities cables was, upon recommendation, removed. The rest of the served stem remains in place steadily decaying further.
Due to the trees location it is not necessary to take any drastic pruning works, I recommend that the dead wood at the top of the canopy is removed as this is likely to fail in strong winds.
From here I would treat the tree as a veteran, monitoring every 12 months with some possible retrenchment pruning works if necessary. SEE CONCLUSIONS
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