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Arboriculture and Tree Energy Dynamics:

Understanding the Maturing Tree

Rex A. Bastian, Ph.D.

The Davey Tree Expert Co.

Wheeling, IL 60090

rbastian@thecareoftrees.com

Consider Trees as a System

� Orderly collection of

parts

� Produce a service

� Require constant

supply of fuel

� Cannot become larger

than the energy

available to power the

system

To Understand How to Care for Maturing Trees, We Must:

� Understand stress and how it affects trees

» To do this, we must also understand:

–Tree anatomy and how trees grow

–The processes of respiration,

photosynthesis transpiration, and

translocation

� Understand how trees allocate resources

-Merker and Hopper, 2005

System Must Maintain “Order”

� “Order” for a tree

translates into

“health”

� As “disorder”

enters the system

» Health

– Stress (reversible)

– Strain (Irreversible)

� The “System”

demands energy

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Energy Required for Every Little Thing

� Stomata Function

» Doesn’t just “happen”

– Closing of leaf stomata

reduces transpirational

water loss

� Also limits carbon

dioxide and water

needed for

photosynthesis

� Also limits oxygen

needed for respiration

Opening- Left and closing- right; http://bio.fsu.edu/ www.gopixpic.com

Tree Begins with Energy Reserve

� More energy

needed as tree

grows to start

the system

each year

Energy Determines the Ultimate Size of the System

� You can start with a

healthy, small tree

and keep it healthy

and small

� Can’t take a healthy

large tree and turn it

into a healthy, small

tree

Tree Physiology

� The study of processes

that take place inside at

tree

» Photosynthesis

» Respiration

» Transpiration

» Absorption

» Translocation

» Growth and Development

» Defense

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Photosynthesis

Chlorophyll (Leaves and

Green Twigs)

Carbon Dioxide

(Air)

Oxygen (Air)

Water (Soil)

Light Energy

Light Energy

ChlorophyllWater + Carbon Dioxide Sugar + Oxygen + Water

12 H2O + 6 CO2 ���� C6H12O6 + 6O2 + 6H2O

What Happens to the Sugar?

� Much is used as a kinetic energy source for

respiration

» fuels day to day processes (makes things happen)

� Chained together to make “Cellulose”

» more leaves, roots, wood, etc.

� Chained together to make “Starch”

» stored for future energy needs as carbohydrate

reserves ( Potential Energy )

� Used for fuel to make protective chemicals

Respiration

Sugar + Oxygen Energy + Water + Carbon Dioxide– Reverse of photosynthesis– Sugars are burned to produce kinetic energy for use– Occurs both day and night (even when trees are dorm ant)– Ultimately, this becomes the key process

Purves et al., Life: The Science of Biology, 4th Ed.

TranspirationPulls Water Up Stem

� Loss of water through the foliage in the form of water vapor» As water vapor is lost, water

molecules “pull” each other up the plant

» Direct connections exist from root hairs to leaves

» Rate of water loss is regulated by stomates

– Usually open during day and close at night

» Temperature, humidity, light and other factors all influence transpiration

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Absorption/TranslocationWater Moves into Root By Osmosis

� Plant cells have more solutes in their interior than does water in the soil» Water moves from low

solutes to high solutes– Same principle as used

in pickles or salted meats

» Requires no or little energy» Once water reaches xylem

tissues in root, transpiration pulls water molecules up the tree

Direction of water movement

MembraneDissolved Solutes

Absorption/TranslocationPassive and Active Uptake of Nutrients

� Passive Transport -

movement of nutrients from

higher to lower

concentration (Diffusion)

� Active Transport - root

selectively transports

nutrients across plasma

membrane and into the root

against concentration

gradient

» Requires Energy

Translocation

� Food (sugars and other compounds) are

moved in phloem tissues

» Sources (where made)

– Leaves/green twigs

» Sinks (where needed)

– Fruit

– Seeds

– Young foliage

– Root tissues

� This movement can be up, down, or

sideways in the tree» Loading the phloem requires energy

� The phloem, like the cambium, is very

thin and easily damaged

Growth

� Tree Growth depends on two “pumps”

» One produces water and elements

» The other produces energy

� Each depends on the other

» If one begins to fail, the other will soon follow

� Growth and health depend on how well both pumps can function together as

the tree grows larger, demanding both more potentia l and kinetic energy

Water and Elements

Energy

Image Courtesy of the Morton Arboretum

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Trees are Generating Systems

� They must grow to

survive

� They can grow fast

or slow, a lot or a

little, but they must

grow

» They have no choice

� If trees stop

growing, they die!

Photosynthesis Vs Growth Vs Defense

� Can there be

too much of a

good thing?

� What about the

low/moderate

range?

How Does Nature Handle the Situation?

Trees Allocate Resources

» Metabolism

» Growth

» Reproduction

» Defense

� Tree must finance all of these

� Maintaining a high level of

potential energy is key to long

term health

Growth Strategy and Life Expectancy

Growth

Defense

Storage

� Trees allocate energy to

growth and defenses

differently

� Resulting life expectancy

vary based on growth

strategy

» Poplars ���� 60 years

– “Live Fast, Die Young”

» Oaks ���� 200-300 years

– “Slow and Steady Wins

the Race”

GrowthDefenseStorage

Fast Growth Tree Species

Slow Growth Tree Species

Quandary--Which is More Desirable?

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Resource AllocationUnequal Incomes

GrowthDefenseStorage

GrowthDefenseStorage

� The tree with the

greater income

can allocate more

to each use, but

maintain the

balance

Tree Defense SystemsCODIT

� CODIT can be hard to visualize» Key points

– It’s a survival mechanism– Wood that forms after

wounding is more resistant to decay

– Trees may become hollow as a result of CODIT

– Decay spreads vertically faster than sideways and outward

� Requires Energy, but is funded at low priorityUSDA Forest Service

Prioritization of Resources

1. Maintenance of living tissues (Respiration)

2. Production of fine roots

3. Flower and seed production

4. Primary growth (elongation of shoots and roots)

5a. Secondary/Diameter growth

5b. Defensive chemicals

Oliver and Larson, 1996

Mass and Energy

� Must consider two different ratios

» Potential to Kinetic Energy Ratio

» Dynamic to Static Mass Ratio

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Energy Makes and Allows Things To Happen

� Potential Energy

» Reserve (Stored)

– Short term (Checking)

� Glucose

– Long term (Savings)

� Starch Reserves

» Allows system to get

larger

» Maintains kinetic energy

� Kinetic Energy

» Active Energy (Metablolism)

» Pays the bills

– Think Wallet (Cash)

– More leaves, wood, fruit,

defensive chemicals, etc.

» Makes system larger

» Maintained by potential

energy

Growth Beyond Potential Reserves Risks Reserve Depl etion

Dynamic vs Static MassDynamic Mass: Tissues that are alive and functioni ngStatic Mass: Tissues that are dead or not actively functioning

• As Trees Age:– Static mass increases relative to dynamic mass– Potential/Kinetic energy ratio decreases– Demand for carbohydrates increases

– Volume of respiring tissues increases while photosy nthetic volume remains fairly constant

Mass/Energy Ratio

� Small Trees tend to grow faster

� Large trees tend to grow slower

� As trees age, energy requirements

increases exponentially

» Reproduction

» Wounds accumulate

– Require barrier zones

� Larger size means more ability to

produce energy

» More energy needed to start system

each spring

May 25, 2016

July 20, 2016

The Core/Skin Hypothesis

� Trees try to deal with

the energy/mass

quandary

� A Tree is a Series of

Overlapping Trees

» Trees use this principle

to enable them to “shut

down” the “inner” trees

to reduce energy

demands

USDA: Forest Service

Shigo, 1989

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Tree System Adjustments

� Trees adjust by

reducing dynamic

mass

» Shed parts

» Shut down older,

inner core trees to

form heartwood

� Requires energy

to form, but

afterward, no

energy to maintainUSDA: Forest Service

If Trees Can’t Adjust

� Health gives way

to stress which

can lead to strain

» Decline

–Whole tree

» Dieback

–Part of tree

If It Can Adjust

� May observe a

“reset” of the

trees growth

pattern

» “Turned a corner”

» “Got back on its

feet”

» “New lease on life”

Enough Energy Must Constantly Enter System to Maintain Order

� As Arborists, we

must:

» Understand limits

» Know when added

energy gains little

» Know when to

recommend “pulling

the plug”

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Tree Age vs. Pruning Dose

� The older, more

mature a tree

becomes, less live

wood and more

dead wood should

be removed

Shigo: Modern Arboriculture

ive wood ead wood

Young

Mature

Over-maturePru

ning

Per

cent

age

Tree Age

D/S Mass ���� HighP/K Energy ���� High P/K Energy ���� Low

D/S Mass ���� Low

Over-Pruning/Construction Injury and Sprouts

� Loss of too many

leaves or injury to

root system can

lead to excessive

shoot formation

» Indicates the tree is

using energy

reserves

» Attempting to return

energy to tree

Liontailing

� “Reverse Topping”

� Removes interior leaves

that function better under

high temperatures

� Leads to overextended,

structurally weak

branches

� Reduces local energy

reserves

Fertilizers Are Not Plant Food

pH Drops

NO3-

HCO3-

HCO3- + H2O = H2CO3 + OH-

pH Increases

NH4+

H+pH Drops

Do not add energy to the system

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Trees and TurfSo, What Makes the Most Sense?

� Whenever possible, try to separate the two systems» Allows each system to be

managed most effectively

» Avoids the conflicts

� Identify the most important plant group occupying the area, and optimize the management of that group

Trees Are Fighting A Losing Battle As They Age

� The tree is committed to

increasing its mass

� With limiting resources ,

the tree regulates its

dynamic/static ratio so that

kinetic energy demands do

not exceed potential

energy reserves

� It can’t keep doing this

forever!Image from Shigo, Modern Arboriculture

Patterns of Death in Landscape Trees� Structural Failure

– Branch, crown and stem failure, uprooting, decay, girdling

� Environmental Degradation» Acute

– Flooding, fire, vandalism, construction injury, drought, high/low temperature

» Chronic– Soil toxicity, soil

compaction, air pollution, restricted growing space, low fertility, severe pruning

� Parasitic Invasion– Insects, fungi, bacteria,

viruses, mycoplasma-like organisms, parasitic plants

1989

1998

1994

The Decline Spiral

� Predisposing Factor

» Diminishes vitality from optimum

» May not be noticeable

» Long term

» Character of tree or physical

environment

� Inciting Factor

» Especially damaging to Predisposed tree

» Short term

» Often very noticeable

» Physical or biotic

� Contributing Factor

» Perpetuates decline of already altered

tree

» Long term

» Effect often very noticeable

» Often opportunistic insect/pathogenImage/Text from Manion, Tree Disease Concepts

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The Decline Spiral

USDA Forest

So, Why Do Trees Die?

� And finally, Respiration Terminates

» Which leads to carbohydrate production

ceasing and/or carbohydrate stores being

exhausted

–Then, photosynthesis slows or discontinues

� Factors necessary for photosynthesis are

unavailable, interrupted, or obstructed

» Because of physical, biological, environmental

or human factors

Healthy vs Unhealthy

� May vary by tree part

� The “System” has high energy demands» Limitation on

energy will result in ruthless changes

» Ultimately, the tree runs out of energy

� Understanding that system will make us better arborists

1989

1998

1994

Summary

� Each part of a tree’s anatomy contributes to its survival

� Photosynthesis produces energy, respiration uses that energy, and transpiration keeps trees hydrated

� A tree’s vascular system is responsible for moving water, nutrients, and foods to where they are needed

� Trees defend themselves from insects and diseases, but ultimately, run out of energy