Arborists will be all too aware of the benefits of formative pruning young trees, particularly where they are present within an urban environment (near to highways, properties, power lines, or otherwise) or have structural issues (co-dominant forks). However, how can the monetary benefits associated with formative pruning be quantified, and if they can be quantified, what does this mean for those who opt not to formative prune?
This study looked at five tree species: Corymbia citriodora (x48), Platanus × acerifolia (x104), Pyrus calleryana cv chanticleer (x79), Quercus palustris (x65), and Ulmus parvifolia (x52). All the trees (348 in total) of these species featured in the study were 3-5 years of age, and no more thn 6.5m in height. Data collected were: health, structure, form, height, and canopy / stem defects.
Following inspection, 78% of the trees were identified to have had structural defects (at least one) that required remedial works, and these remedial (formative) works were done with secateurs, a hand saw, or a pole pruner – the latter was most frequently used. The table below shows, in more detail, the average number of cuts (and with what instruments) per tree for each species.
The time taken to undertake each cut was also noted, and the data is shown in the table below. By calculating the amount of time it took to prune each tree, the cost in man hours could also be calculated, and the average cost per tree (across all five species) was $2.79 AUD.
So how does this average cost compare to pruning mature trees? The authors acknowledge that the pruning of eucalypts of 20 years of age costs $78-112 (adjusted for inflation) per tree. When put against the cost of formative pruning young trees, there really is a massive difference (even if young trees receive formative pruning two or three times in the first six years of their life, which may amount to up to $7).
Not formative pruning young trees therefore makes little financial sense, and also opens up the tree to far more significant structural issues in maturity. For example, co-dominant stems were frequently observed in this study. The removal of such forks when young is easy and has little impact upon the tree, though in maturity not only may the fork have bark incluson, but dealing with the issue is far more difficult and only ever going to be a firefighting measure that costs a lot of money each time.
Perhaps formative pruning could even help local authorities, who have less money available to them than in years gone by. Granted, this won’t apply for trees already in maturity, though where new trees are planted ensuring they are formatively pruned can really have marked financial benefits.
Source: Ryder, C. & Moore, G. (2013) The arboricultural and economic benefits of formative pruning street trees. Arboriculture & Urban Forestry. 39 (1). p17-24.
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