Tree pruning is the most visible arboricultural task that we encounter in the urban forest. For public tree managers and commercial arborists, handling client service requests pertaining to tree pruning is a daily part of the job. For utility vegetation managers and utility arborists, electrical or telecommunications line clearance are central to their respective missions. In the nursery, many tree growers and even researchers have adopted approaches to develop "city ready" trees, using pruning to create tree forms and structures that prepare young trees for urban conditions.
Pruning is the selective removal of plant parts to achieve an objective. Earlier in this course, we studied how the removal of leaves, branches and stems can alter and even disrupt certain physiological processes in trees from photosynthesis to transpiration to defence, and beyond. Although, pruning can be necessary to reconcile physical conflicts between trees and human activities, to mitigate risk or respond to aesthetic objectives, scientific observations inform us that every cut has a consequence. With this in mind, it is important for arborists to consider a tree's response as well as its health and condition, over the long term, when prescribing and conducting pruning operations.
The beginning of any successful pruning project should incorporate an assessment of the tree(s) to be pruned, understanding the particularities and needs of the species as well as tree size, health and condition at the time of work, time of year of the intervention and any site conditions that could affect the tree's health or the nature of the work. Considering the site is crucial, as some constraints may imply safety issues requiring preventive action before work begins (example: presence of overhead electrical wires or close proximity to a busy street).
After evaluating the most important variables of the tree and the site, another equally important part of tree pruning is to establish objectives and clear guidelines for the work to be performed. Objectives should respond to the request at hand while intervening ideally to prevent or at least mitigate the physiological impact of pruning on the tree(s).
Most importantly, tree pruning work should be conducted by qualified professionals with the appropriate training, knowledge, experience, procedures and equipment to perform the job safety, according to specifications.
This week, we will cover the main reasons why trees are pruned in urban landscapes. We will compare the most common pruning goals with specific pruning types as described in North American pruning standards. In this course, you will have access to different international pruning standards and will be able to explore these comparisons in your research and assignments. We will also review some fundamental concepts about pruning cuts, focusing on cut types and cut locations. Pruning cuts can profoundly affect tree response and health over time, depending on how they are carried out, when and to what extent.
This section's readings will provide an overview of pruning operations - how and why they are performed on urban trees. Pruning remains very specific to each tree and each site. Although, some of the principles covered in this course are commonplace, our understanding of the effects of pruning, and of the most optimal ways to intervene, are challenged by variability, lack of industry consensus and limited research in urban settings. Nevertheless, tree pruning is a fertile topic for contemporary research as advanced studies in tree biomechanics, tree allometry, formative pruning and the effects of utility pruning are introduced to academic journals and conference agendas, so keep an eye out!
Learning Objectives
By the end of this topic, you should be able to:
Understand the objectives and reasons that drive tree pruning operations in urban forests
Identify variables that can affect tree health and condition when prescribing and undertaking tree pruning work
Recognize industry best practices for tree pruning
Be aware of different approaches, schools of thought and resources that can inform tree pruning decisions
Looking to get up to speed on tree pruning in general? Consider this optional reading to introduce you to the topic and fundamental concepts about pruning trees. This guide provides an array of useful drawings to illustrate different pruning types and cuts, however, it is important to examine and become familiar with in-person cases when developing one's expertise in tree pruning. This is a handy start for people who are new to the discipline.
Gilman, E.F. (2012).All Illustrated Guide to Pruning, Third Edition. Delmar Cengage Learning, Albany, NY
Optional Reading
Deep dive on utility pruning - electrical line clearance
If studies on the impact of electrical line clearance on urban trees in temperate climates are of interest to you, the NSERC/Hydro-Quebec Research Chair on Controlling Tree GrowthLinks to an external site. would be an interesting stop for you. You can check out there website which includes list of publications, active research team and projects. The site can be translated easily using Google Chrome. Here are some selected publications comparing tree physiology and line clearance pruning.
Lecigne, B., Delagrange, S. and Messier, C. (2018). Crown reaction and acclimation to cyclical V-trimming of city trees: An analysis using terrestrial laser scanning. Urban Forestry & Urban Greening, 29 (pp. 183–191).
Perrette, G, Delagrange, S., Ramirez, J.A., and Messier, C. (2021). Optimizing reduction pruning under electrical lines: The influence of tree vitality before pruning on traumatic responses. Urban Forestry & Urban Greening, 63.
1. In your community, are all tree pruning interventions justified? Can you think of some examples of cases where tree pruning was necessary, and other cases where it was less so?
2. Describe the ways in which pruning can have an adverse effects on tree health and condition. Do certain types of pruning have more effects than others, which ones and why?
3. How can municipalities manage their urban forest, over the long term, to avoid physical conflicts between trees and human activities/structures? What strategies and interventions could be done, at all life stages of the city's trees?
UFOR 521, M. Hanna, 2021
Requirements Changed
Topic 3.1: Introducing Urban Tree Care Topic 3.3: Integrated Management of Tree Pests and Diseases