Understanding how trees function, and what they require to reach maturity, is central to managing a sustainable urban forest. Insight on plant sustenance, growth and defense can lead to better decisions about tree care, thus maintaining trees on the landscape.
Trees experience complex interactions, influenced by their genetic traits and their environment. Researchers who embrace this complexity and study tree anatomy and function are capable of discovering new characteristics about trees. New perspectives about how trees grow can even challenge conventional approaches to tree care, leading to advancements in the practice of arboriculture.
This week, you're invited to observe a tree, how it grows, how it differs from other trees and how it responds to its surrounding environment. Think about this as you approach the assigned readings.
The balancing act continues, as we explore a three part series on tree physiology and its relation to urban constraints. This week we look at how trees balance their biological needs with factors in the urban environment
This week's readings are on the heavier side as we delve into the biological, chemical and physical functions of trees. What you will learn in this portion of the course, is designed to carry through and remain front of mind as we explore different aspects of tree care.
Learning Objectives
By the end of this topic, you should be able to:
Identify and describe the main biological processes that are vital to the growth, development and survival of trees
Discuss the two main variables that influence tree physiology
Understand how trees grow as well as the organs, tissues and elements involved in this process
Define plant stress and explain why this concept is important in the context of urban tree care
Recognize how knowledge of tree physiology can challenge pervasive practices (topping, lopping, whole branch removal)
Topic Readings
This week, we explore tree physiology and the processes essential for tree growth, development and survival.
Required Readings
Material covered in the following chapters will be relevant for the mid-term exam
Hirons, A. & Thomas, P. (2018). Applied Tree Biology. Wiley Blackwell (Chapters 2,3,4,6 and 7 - 206 pages total by week 6) .
Optional Readings
Looking to get up to speed? Consider these optional reading for more a basic introduction of tree biology and terminology, should you feel the need.
Lilly, S.J. (2010). ISA Arborists’ Certification Study Guide. International Society of Arboriculture, Champaign IL (Chapter 1).
Want to dive a little deeper? Consider these optional readings to learn more and explore topics of interest in greater detail.
Pallardy, S.G. (2008). Physiology of Woody Plants. Elsevier. Burlington MA.
Drénou, C., Restrepo, D., and Slater, D. (2020) Demystifying Tree Forks: Vices and Virtues of Forks in Arboriculture. Journal of Botany Research. 3 (1): 100-113.
Tree physiology is the study of the biological, physical and chemical processes vital to the growth, development and survival of trees.
This course obviously focuses on trees, perennial, self supporting, woody plants with one or a few prominent stems as well as branches forming a distinct crown (Hirons 2018).
Tree physiology is influenced by a tree’s genetic traits as well as by the environment in which it grows. Sometimes the conditions of an environment cancel out or compromise the efficacy of a tree's inherent traits (see example, pages in Hirons following Figure 2.1 - 93 and 94 in e-book or example of tree crowns at e-book page 235).
Despite their complexity, we can summarize the main physiological processes of trees into three categories:
Sustenance - how a tree acquires energy and nutrients and how that energy is used with in the tree.
Photosynthesis
Respiration
Absorption
Transpiration
Translocation
Synthesis of proteins, lipids, hormones and other compounds
Growth - how trees grow the way they do and why.
Vegetative growth: primary and secondary
Reproductive growth
Growth regulation and dormancy
Defence - how trees manage injury, damages and other threats.
Compartmentalization of Damage/Dysfunction in Trees
In arboriculture, it is immensely useful to be able to identify and describe these processes along with their objectives relating to tree development and survival. Knowing the inputs that going in to these process as well as the environmental factors that affect them help guide logical interventions, as needed, if needed at all.
It is important to understand and be able to explain two reasons linked to tree mortality - carbon starvation and water deficit leading to hydraulic failure.
Looking at tree growth and development from a perspective of balance also has the potential to influence sustainable interventions that keep trees in equilibrium with the environment.
This course sets out to provoke thought and the reconsidering of a few pervasive practices such as the systematic elimination of sprouts and forks. These practices will be explained and discussed in greater detail during the course, but it's worth looking at the phyisiology of these components first.
STRESS: An environmental factor that reduces the rate ofa physiological process within a plant or one of its constituent parts.
VITALITY: A trees’s ability to deal effectively with stress, efficacy of the plant’s response to physiological stress.
Self Check Quiz
1.2 Practice Quiz
As you learn the course content, consider trying out this optional practice quiz to see how you're understanding course concepts and ideas.
To be released during the week of this lecture.
Activities & Assignments
Online Discussion #
No Assignment this week. Kindly take the time to get into the readings.
Topic Summary
To be released during the week of this lecture.
Topic Self-review
Here are some thematic questions to consider as you continue on your journey. We will discuss these questions together in this week's seminar.
1- Discuss ways in which the urban environment helps or hinders physiological process in trees. Bring in an example you experienced or bring up an example you learned about in the readings.
2- Do you believe that a better understanding of tree physiology can promote smarter interventions in tree care? Which physiological processes are the most important? Which practices can be improved? How? Let's talk about it!
3- What can tree physiology tell us about balance when incorporating and managing trees in urban settings? How is balance addressed in literature that we reviewed on Monday?
Meagan Hanna, 2021
Requirements Changed
Topic 1.1: Striking a Balance: Reconciling Tree Development and Human Development (Course Introduction) Topic 1.3: Abiotic Factors Contributing to Tree Development and Condition