A study of the effects of paclobutrazol on the growth rate of fast growing tree species

Abstract

A detailed investigation was conducted into the use of growth regulators to slow the development of fast growing tree species in close proximity to overhead power lines. Four fast growing tree species were selected: Acer pseudoplatanus (Sycamore), Tilia X europea (Lime), Fraxsinus excelsior (Ash) and X Cuprssocyparis leylandii (Leyland Cypress). The trial site was located at Myerscough College, northwest England. The tree growth regulator 'Cultar' (active ingredient paclobutrazol) was applied to five trees (treated) in each species, a further five of each had the same amount of water applied (blank) and the remaining five trees of each species provided the control. All trees were pruned prior to treatment. One application of Cultar was administered at the commencement of the three-year trial period. The extension growth of all trees was recorded over three growing seasons from 1999 to 2001. In the last growing season the leaf size and chlorophyll content of the leaves of all the trial trees were also recorded.
Following statistical analysis of the data, the results demonstrated that it is possible to control the growth of some of the selected species using Cultar. The treated trees of the following species grew significantly less than the blank and control trees of the same species (p<0.05): Ash 18.7%, Lime 18% and Sycamore 55.4%. Due to external influences, the Leyland cypress data was unreliable and no conclusive evidence could be gathered which would indicate whether the treated cypress were significantly regulated or not. The research raised a number of issues: notably, the experimental design, method of application of the growth regulator and timing of the application. The successful results have provided further impetus for research into the use of tree growth regulators and their eventual inclusion into vegetation management programmes in the United Kingdom and Ireland.