A Tree's Defense
As humans, we all enjoy being able to pick up and go wherever we desire in life. Whether we get
somewhere by walking, running, riding a bike, driving a car, or taking a plane. In fact, this very basic part
of our existence is absolutely taken for granted, don’t you agree?
Imagine being a tree. A tree is literally stuck in the location that it was originally planted forever. Can
you perceive this? You’d better get used to your surroundings and environment rather quickly if you’re a
tree, and become truly adaptive.
This reading will explain the functions of how a tree allocates its resources to survive healthy and
vigorously. Including how a tree defends itself in its solitude environment; especially if a tree has the
raw end of the deal. For example, if a tree has grown very close to a place that disposes waste material,
or it’s a city tree next to a busy street with concrete covering its root system.
Let us start by understanding the basics of a tree. A tree is a woody plant. There are many species of
trees, categorized in 2 types – deciduous (mostly hardwoods) and conifers (evergreens). Just like us,
trees must have sun, water, and nutrients to survive. You have probably heard that without trees, our
environment would become toxic quickly. Trees take in carbon dioxide and emit valuable oxygen. Yes,
that’s right - trees are natural air filters. Over the past decade, we have come a long way to scientifically
understand a tree. From this information, we have realized that trees have a biological make up that
make them very dynamic. They are made up of much more than just a crown, trunk, and roots.
Trees allocate their resources in 4 primary functions;
Maintenance
Growth
Storage
Defense
If a tree has to deal with toxic waste and poor soil conditions, it still has to maintain itself. A tree gets its
energy from photosynthesis. A tree uses energy for regular procedures such as seed formation and
dropping.
Trees grow optimally when they have all the elements that they need and are not stressed. If a tree does
not have adequate water, light, and nutrients it will not likely dedicate too many resources toward new
growth. Proper soil PH balance, soil conditions (acidity), and availability of resources are critical in the
growth process.
Trees obtain nutrients, and water from the ground using their fibrous roots. If essential minerals and
water are not available in the quantities necessary, a tree will concentrate on storing essential elements
for later use. For example, if a tree does not have sufficient water it will store water to get through
drought spells.
A tree will allocate its resources to defense if it is getting most of what it needs, and is not stressed. Soil
and environmental conditions determine whether a tree is stressed or not. If a tree is not stressed, it will
likely be in a preventative maintenance mode and will focus on defense. For example, a tree can focus
on thickening its bark layer to protect its vascular cambium from outside predators. Did you know that a
tree produces chemicals to defend itself from other competitors? Yes, a tree will send warning signals to
its surrounding opponents whether it is a plant, insect, or other close by organism. If a physical wound
occurs, a tree compartmentalizes. Remember, humans heal and trees seal!
A tree is truly a genius in the process of making something out of nothing, or coming up with a way to
survive in harsh conditions. It cannot just walk into a doctor’s office and ask for an antibiotic. It does not
have an immune system to fight a virus. But a tree will produce chemicals, and close off its vascular
system to outside organisms if being intruded. If a stressor (usually environmental) is too much for a
tree to overcome, then it will go into decline and potentially even die. In our famous street tree example
above, with lack of available water or nutrients nearby - the root system of that tree will sense resources
from far away and start growing its roots more progressively to one area or direction toward the
available elements.
So next time you drive or walk by a tree, take a good look at it. Understand its ability to survive even in
low tolerable conditions. Think about its ability to go through all the daily functions in the spot that it
stands. Take a look around at nearby obstacles such as construction sites, chemical exposures, insects,
geographic makeup. Appreciate a tree’s ability to live in a confined nature, and how it can defend itself
even without being able to get up and walk out of harm’s way.
Written by - ISA Certified Arborist Sean Lewett
Reference - Arborist's Certification Study Guide, ISA, 2000