Arboriculture & Urban Forestry 39(1): January 2013 Arboriculture & Urban Forestry 2013. 39(1): 17–24 17 The Arboricultural and Economic Benefits of Formative Pruning Street Trees C.M. Ryder and G.M. Moore Abstract. Research was undertaken to determine the need for, and costs of, formative pruning recently planted street trees. Specimens of Corymbia citriodora (48), Platanus × acerifolia (104), Pyrus calleryana (79), Quercus palustris (65), and Ulmus parvifolia (52) were surveyed. Health was similar for all species, but form and structure varied. Data showed that codominant stems (68%) and included bark (40%) in the canopy or trunk were by far the most common structural defects. Codominant stems were reported in 92% of all Ulmus parvifolia, 66% of Quercus palustris, 61% of Pyrus calleryana, 44% of Platanus × acerifolia, and 19% of Corymbia citriodora. The number of trees of a species that displayed no struc- tural defects was 25% or less except for Corymbia citriodora with 60% showing no structural defects. The pruning required to rectify these structural defects was recorded and then multiplied by a time factor for pruning with secateurs (hand prun- ers), a handsaw, or a pole pruner. Total time was then converted to an economic cost using current labor market prices. Platanus × acerifolia required the most work per tree with a final formative pruning cost of AUD $4.13 followed by Ulmus par- vifolia ($3.25), Pyrus calleryana ($2.76), Quercus palustris ($1.62), and Corymbia citriodora ($0.99). This compares with an aver- age cost of $44.59 per tree for structural pruning 20 year old trees. Formative pruning makes sound arboricultural and economic sense. Key Words. Arboricultural Labor; Cost Benefit Analysis; Natural Target Pruning; Tree Management. Directions on how, when, and what to prune have been published widely (Pirone et al. 1988; Gilman 1997; Harris et al. 1999; Gil- man 2002; Joyce 2002). Knowledge of the role of branch bark ridges and collars has meant that pruning is done in a similar way to the tree’s natural shedding processes (Moore 1992). This is consistent with good arboricultural practice and sound biological principles. By removing branches early, wound size is reduced as is the time taken to grow over the pruning cut by the produc- tion of callus and woundwood. The implementation of good for- mative pruning as part of a tree management plan is essential. Formative pruning has long been advocated as good arbori- cultural management, but is too rarely practiced (Moore 2003). It can be defined as the selective removal of stems and branches early in a tree’s life to create a safer, stronger, and more aesthetic structure. Many of the problems and defects of mature trees can be traced back to structural defects early in life. The loss of api- cal dominance and the occurrence of codominant stems have been linked to transplant shock, pest attack, and water stress in Fraxinus pennsylvanica (Oleksak et al. 1997). If these defects continue into maturity, the result may be a tree that is structur- ally weak (Gilman 2003), requiring significant remedial work to its structure that creates large wounds. This is more time-con- suming than pruning lateral buds or small stems as they occur. Although pruning costs have been calculated in various ways, there is little information on calculating the costs and benefits of formative pruning. If a tree is formatively pruned in the early stages of life, what will the cost-saving be if the same defects had not been rectified? For example, if a codominant stem is removed from a young tree at a height of three or four meters, with a pole pruner, what is the cost? If this same stem is left for 10 or 20 years and then has to be removed, or if one of the codominant stems has to be removed, what is the cost? The purpose of this study was to look not only at how formative pruning can improve a tree’s structure, but to quantify the finan- cial benefits of removing structural defects early in a tree’s life. Over time, the early removal of many hazards would allow more funds to be diverted from reactionary maintenance and removing hazards to the proactive management of the urban tree resource. METHODS Data were collected for five commonly planted street tree spe- cies in Melbourne, Australia: Corymbia citriodora, Platanus × acerifolia (syn P. hispida, P. hispanica), Pyrus calleryana cv chanticleer, Quercus palustris, and Ulmus parvifolia (Table 1). The trees selected were young (3–5 years of age) and un- der 6.5 m in height. Data were gathered on tree identification, health, structure, form, height, and canopy and stem structural defects. Tree form relates to the shape of a tree and, regard- less of mature excurrent or decurrent form, a central trunk with radiating branches is what is often desired in urban street trees. Excurrent form has a tendency to a central lead- er that remains superior to the lower branches result- ing in a conical shape. In nature, most vigorous young trees, regardless of their adult form, have this form. Decurrent form is where the lateral branch- es outgrow the main leader or trunk and form a more rounded, spreading canopy (Harris et al. 1999). ©2013 International Society of Arboriculture
January 2013
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