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“Pollarded” lime tree pollarding, one must admire the tenacity of limes (Tilia spp.). The second image set shows a maturing small-leaved lime (Tilia cordata) that was initially ‘topped’. There were some large diameter cuts to start with, recut the following year and then allowed to regrow a full crown – as can be seen 12 years later. This is certainly not professional tree work, but it does show the great tenacity of this species and how it will attempt to regrow its crown despite severe reduction. It’s important to see ‘topping’ and ‘pollarding’ as a continuum rather than setting a closed definition that separates them entirely. Poor pollarding to a tree unsuited to that treatment can be as bad, if not worse, than topping a young tree. The lime will come back from such ruthless butchery repeatedly, and for most trees, do not follow the guidance in ‘Modern Arboriculture’ concerning annual re-cutting. There needs to be su cient regrowth. he conse uences o ushing The third set of images show a four-year time-lapse of a flush cut to a young oak tree (Quercus robur L.) in a churchyard near to me by an amateur. If you look at the shape of the re-growth, you can see that the top and bottom
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Pro Arb | Summer 2019
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Twelve years later... of the wound are slower to close than the sides, because the tree’s trunk tissues have been damaged by this overly-close flush cut. Even if you do a good cut based upon natural target pruning (NTP), you mustn’t expect to see a doughnut-ring of callous around every cut you’ve made the next year. A saw cut breaks the ‘sealed unit’ of a tree, lets in air and microbes to the inner back – causing that to partially die back and dry out because of the cut. It is like the cambium takes a step back before it can come forward again to occlude the wound. What would have happened if a cut based on NTP had been carried out to this tree? Firstly, the trunk would not have been
damaged directly – so that’s surely a good thing. Why damage the trunk when removing a branch? Additionally, the wound would have been smaller in diameter and would have closed quicker. t looks to me that this flush cut is going to take six to seven years to close: a correct NTP cut would have closed in three to four years. For this particular cut, where the branch was only about 750mm (3 inches) in diameter, this flush cut is not going to have big consequences for this young oak. Scale that up to a larger cut on a tree that is growing more slowly, and that difference in closure rate becomes much more important. The scientific research that backs up NTP principles is robust. If your intention is to minimise pruning wound size and the risk of infection or decay, nothing yet beats the NTP recommendations, which our current British Standard for tree pruning (BS 3998:2010) is currently based upon. hink o the conse uences When a tree is topped or heavily crown-reduced, this has lifechanging consequences for the tree. It will never return to a fully natural shape – cuts may
induce early-onset decay in the tree and, at times, re-growths may not be well-attached and can fail in strong wind. However, recovery is possible, particularly if the tree was relatively young when severe cutting was done and the re-growths managed to prevent natural bracing occurring, encouraging a suitable crown shape to develop. The species matters. Rapidly re-growing sprouts on a topped mature poplar tree will be liable to break off as decay sets in to the large diameter cuts. Slower growing shoots of a topped yew tree will cause little problem in nearly all scenarios. With urban tree populations under threat, find the willingness of some arborists to dismiss the potential value of a topped tree disturbing – many do recover to be trees of considerable aesthetic and ecological value. f an unlucky person sets off an IED, causing life-changing injuries, their life will never be the same again. However, their wounds heal and over time they make a meaningful amount of recovery. In that state, does the doctor then decide to condemn them as a ‘low-value’ person? Fortunately,
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Flush cut to young oak tree
Two years later...
Four years later...
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12/08/2019 08:57