Dr Glynn Percival of Bartlett Tree Research Laboratory based at the University of Reading, together with US-based Bartlett colleague Tom Smiley, investigated the effect of different percentages of stem girdling in both winter and spring on semi-mature birch (Betula pendula) and English oak (Quercus robur) trees over a five-year period.
All the oaks survived any amount of girdling irrespective if girdled in spring or winter, they found. Birch trees were more sensitive to girdling with all dying after 100 per cent winter girdling and 40 per cent of trees dying after 100 per cent spring girdling.
Less severe girdling, of 25 and 50 per cent, was found not to affect the growth and vitality of either species. More severe girdling had a greater effect on oak growth and vitality if performed in spring.
Trees which survived for three years after girdling were "in virtually all cases, statistically comparable with non-girdled trees", they concluded.
The study is published in the journal Urban Forestry & Urban Greening.