Almost 400 tree care professionals attended the event, which has become an important annual meeting for arborists. Until recently, almost all research on transplantation has concentrated on aftercare. However, Dr Glynn Percival of the RA Bartlett Tree Research Laboratory found that the addition of carbohydrate, in the form of sugar, prevented leaf necrosis and other signs of stress. This sort of preconditioning could be administered in nurseries to improve trees' stress tolerance, he suggested.
Percival also experimented with adding a high-nitrogen slow-release fertiliser and with adding the growth inhibitor PBZ. These also promoted tree vitality. Of the three substances, PBZ had the most significant effect.
The keynote speaker at the conference was Dr Gary Watson of the Moreton Arboretum in Illinois, USA, who explored the importance of root development in city trees. He pointed out that if roots were allowed to grow downwards without any limit, tree growth was slower. He therefore advocated not hampering root growth in towns.
Watson found that microroots have an enormous environmental importance. When a tree is moved, 90 per cent of its roots - in the form of microroots - are left behind. He also suggested that mulching can help the development of roots by improving the supply of nutrients. However, he warned against piling up mulches around the base of trunks.
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