Tina McKeand
Urban & Community Forestry Specialist
© 2005 Tina McKeand
Trees
have been living on this
earth for 360 Million Years.
Mankind
has only been here for 2
million years.
Trees are Complex
Organisms
Like people, trees
are complex living
organisms
And
Just like people,
each tree is an
individual
1
A tree planted today in an
urban location often has a life
expectancy of only
7 -10 years!?!*
*Alex Shigo, Modern Arboriculture, p vii, 1991
Making the Cut?
Things to consider . . .
™
Why we Prune?
™
What to Prune?
™
How to Prune?
Compartmentalization
Of
Decay
In
Trees
2
TREE BIOLOGY 101
the vascular system
Meristems
xylem
bark
phloem
skin
.......
Like
arteries
veins
- AreasLike
of cell
division/growth
transports water
sugar
transports
protects the
from
the leaves
to
and
nutrients
-Also found
at tips
of from
vascular
system
growing
points
in
the
the
ground
into
the
roots
and shoots
from
infection
tree
tree
Structure
™
The overall shape of the tree, its
trunk, roots, and branches
™
And, the nature of its branch
attachments
Structure is
determined by . . .
™
Genetics
™
Environment
3
Wild trees develop healthy structure by
properly managing the limited resources in
their
NATURAL environment
Often . . .
Commercially Grown Trees
Receive
Too Many Resources
&
Too Little Space for Growth
For many nursery grown trees . . ,
nutrition and water are not a problem,
but space and sunlight are at a premium!
4
STRUCTURE
NATURAL
HEADED
Photo Courtesy of Dennis Swartzell
5
It’s not
NATURAL
to Stake
a Tree
A weak trunk
and a heavy
canopy requires
the support of
a nursery stake
The Cost . . .
Not the Cure!
6
Juvenile Branches
™
Promote healthy trunk taper
™
Aid in wind resistance
™
Provide protection from the sun
7
JUVENILE BRANCHES ARE CRITICAL
FOR DEVELOPMENT OF HEALTHY
TRUNK TAPER
REMOVING JUVENILE BRANCHES
CONCENTRATES WIND IN THE
CANOPY AND PLACES STRESS ON
THE DEVELOPING TRUNK
8
JUVENILE BRANCHES HELP A TREE
RESIST WIND DAMAGE
JUVENILE BRANCHES PROTECT
IMMATURE BARK FROM SUNBURN
9
Juvenile
Branches
“Rule of Thumb”
Remove juvenile branches
when they are bigger
than your thumb!
Why prune?
™
Nature vs. Nursery
™
Conformation to urban needs
™
Promote healthy structure
10
What to prune?
™
Dead or Diseased limbs
™
Crossing & Co-dominant limbs
™
Poor branch attachments
Learn to spot hazardous
structural defects when
the tree is young!
Co-dominants
11
Pruning for Structure
BEWARE . . .
OF BRANCH
ATTACHMENTS
WITH
<45O
ANGLE OF
ATTACHMENT
0O
45O
90O
Branch Bark Ridge
Sign of a healthy branch attachment
12
INCLUDED BARK
Co-dominants
13
Included Bark & Co-dominants
Lead to Catastrophic Branch Failure!
And, may lead to Hazardous Trees
& Liability!
Promote Individual Character
™
™
Every species has unique
characteristics!
Each individual within a species
is unique!
14
Good Pruning is Like a Good
Haircut . . . It shouldn’t be too
Obvious!
How to Prune
™
How Much to Prune
™
Where to make the cut
™
How to make the cut
How much to prune?
™
1-2 years = up to 50%
™
Young trees = up to 30%
™
Middle age trees = up to 25%
™
Mature trees = > 15%
CAUTION!
These are MAXIMUMS . . . Not GOALS!
15
ALWAYS prune
at Branch
Unions
Branch Collar
Branch Bark
Ridge
Proper Cut
Branch
Collar
16
Branch Collars
Branch Protection Zone
*Vascular
intersections
occur at
branch unions
Adventitious
Buds
Triggered by
CATASTOPHIC
INJURY
17
Failure to Prune at Branch Unions
results in many open wounds . . . And
rapid re-growth
Multi-Tip Dieback . . .from pruning
with shears
3 Point Cut
Method
Final cut – Just
outside of the
Branch Collar
18
Using the 3 Point Cut method at a
branch union results in healing callus
Failure to use the 3 Point Cut Method
may result in hideous wounds
that are difficult to heal
Sooner is Better than Later
19
TOPPING Results In . . .
Ins
e
Dis cts &
ea s
es
tion
rv a
Sta
Shoc
k
Weak
Branch
ents
Attachm
Rapid
New
Growth
Ugli
Cost
ness
DEATH
Crown Reduction
20
Tina McKeand
Davey Resource Group
7627 Morro Road
Atascadero, CA 93422
tmckeand@davey.com
928.246.7048
21
The sixth deadly sin of urban tree care is really about
letting young trees be young trees. You might imagine that a
tree fortunate enough to be planted in the right place,
possessing good structure, planted proud, staked properly, and
irrigated optimally wouldn’t have another care in the world.
Unfortunately, it’s a harsh world out there in the big city, and
By Tina McKeand
as a rule, urban dwellers expect instant gratification. Young
trees are often prematurely separated from their juvenile
branches in a misguided attempt to encourage a more mature growth habit.
By definition, any young branch is a juvenile branch, but those most often targeted for removal are
the ones growing on the lower trunk beneath the establishing canopy line. It’s important to note however
that trees of any age can and do develop juvenile branches as needed throughout their lives.
As we know, trees develop according to a genetic plan that has evolved over many millions of
years, long before the introduction of more advanced beings that can’t even produce their own food!
While we are only beginning to understand all of the possible benefits of juvenile branch placement, we
do know that trees grow in a logical manner and it’s a sure bet that they are there for very good reasons.
Thanks to Alex Shigo, Richard Harris and all of the other tireless researchers out there who are my
personal superheroes, we understand at least some of these important functions.
Juvenile branches promote strong taper in a developing trunk. In order to withstand the
environmental forces placed upon it, a tree must develop a strong trunk base that gradually tapers to the
tips of the canopy. But if all of the food is being produced by leaves in the canopy, there might not be a
lot left by the time the upper growing points take their share and the remaining photosynthates trickle
down to the lower trunk. Young trees adjust for this by growing small branches along the trunk to
provide a local “fast food” source to fuel the expanding trunk. Premature removal of these branches
transfers energy towards increased canopy growth at the expense of trunk girth. Trees that are
prematurely stripped of their juvenile branches often develop spindly, weak trunks that require chronic
staking to provide necessary support.
Juvenile branches aid in wind resistance and reduce
the likelihood of damage to the tree. In addition to promoting
healthy trunk taper, which aids in flexibility, young branches
on the lower trunk help by spreading the forces of wind load
over a greater vertical surface. The premature removal of
juvenile branches causes the canopy to act like a sail,
concentrating the force of the wind in the upper canopy. This
action concentrates the wind load at a more specific point on
the developing tree trunk and increases the likelihood of trunk
failure through stress fractures.
Juvenile branches protect young trees from
sunburn. Young bark, like the skin on a baby is much more sensitive and susceptible to sunburn than
mature bark. A fingernail can easily scratch through young bark and into the cambium layer. Try that
with mature bark and you’ll need a quick trip to the manicurist! Juvenile branches protect the tender
trunk tissues by diffusing the intensity of the sun’s harsh rays. The premature removal of juvenile
branches often results in sunscald and peeling bark on the southwest side of the tree. As with all injuries
to trees, the damage is permanent and results in a reduction of vascular flow and an inviting entry point
for wood destroying insects and disease.
Juvenile branches can be found throughout a tree and on trees of any age. They may sprout to
fuel the development of reaction wood for greater strength or in response to decay or disease. Preserving
juvenile branches in the vicinity of larger pruning wounds can promote faster healing through greater
wound wood development (compartmentalization). Wherever they occur, it is best to leave them on as
long as practical so that they can perform their intended function.
Juvenile branches are often quite vigorous and may bravely grow out into parking lots, sidewalks,
streets and other high volume traffic areas. This is unacceptable in an urban environment and they must
be encouraged to conform to the constraints of the community while still performing their vital role. A
juvenile branch that is growing in an undesirable direction can be tipped back to within 12 inches of the
trunk. A reduction cut to a side shoot will direct the juvenile branch to grow in the direction of the
selected side shoot. A heading or stub cut, while never recommended for a permanent branch, will
promote an adventitious cluster of leaves. Either of these treatments will preserve the purpose of the
branch while conforming to societal needs.
In a natural environment, trees shed juvenile branches
when they are no longer needed. If you’ve ever crawled under
a large canopy in the forest you may have noticed the dried up
branch stubs still attached on the lower trunk. Trees naturally
shed juvenile branches once their purpose has been fulfilled.
Shade from the developing canopy eventually reduces sunlight
to the small lower branches and renders them useless for
photosynthesis.
Once there is no longer a return on
investment, the tree cuts off circulation and literally starves
the non-productive member to death.
As mortals, we can’t possibly be expected to exercise
the patience and restraint necessary to wait for juvenile
branches to dry up and fall off, so I promote what I believe is
a reasonable “rule of thumb”. When an undesirable branch
reaches a diameter bigger than your “thumb”, it’s okay to
remove it. Juvenile branches will continue to sprout as long as
they are deemed necessary by the tree. Nature provides the
answers if we are paying attention. A lot can be learned by Juvenile branches should be allowed to remain until
are at least as big (in diameter) as your “Thumb”.
touching and listening to trees. Ah, I hear them whispering they
Tip back branches that interfere with traffic or view.
now . . .I’m off!
Visit www.treesaregood.com for additional information
on pruning a tree and other important topics.
© 2007 Tina McKeand.
Originally published in
Southwest Trees & Turf, June 2007.
tmckeand@davey.com
928.246.7048
Tina McKeand
Davey Resource Group
7627 Morro Rd., Atascadero, CA 93422
Arguably, trees are the most successful organisms on
earth. As a group, they hold bragging rights as the tallest
(Coastal Redwoods), the most massive (Giant Sequoia), and
the oldest (Bristlecone Pines) living beings on the planet. They
produce their own energy and recycle available resources to
molecular levels. As such phenomenal beings, they deserve
By Tina McKeand
our utmost respect and reverence. Unfortunately trees are often
taken for granted, especially when it comes to our community
forests. Examples of improper pruning and topping abound in every community.
While basic proper pruning is not terribly difficult to master, if the intent is to preserve the tree in
a healthy manner, it does require some understanding of tree physiology and biological response. Many
trees are killed and permanently disfigured by well intentioned ignorance and the misunderstanding that
everyone who works in landscape maintenance knows how to trim a tree. Armed with a basic
appreciation of pruning response and recognition of harmful practices, many common errors can be
avoided.
Because a tree is a dynamic, living organism, every pruning cut results in a chain reaction within
the tree, including response to the injury, changes in energy distribution and flow, and a reduced ability to
produce food.
Trees do not heal in response to injury in the same way as animals. Instead of replacing bruised
and damaged cells, trees compartmentalize, or seal their injuries by building barriers and diverting
circulation around the damaged area. These compartments become permanent dead areas inside of the
tree. Internal compartmentalization begins immediately in response to injury. Chemical walls form
laterally, horizontally and radially to prevent the damage or disease from progressing and invading
healthy tissue within the tree. Since tree bark serves as an outer layer of protection, much like our skin,
compartmentalization is not complete until new tree rings grow over and completely cover the wound.
Until this process is complete, the tree is vulnerable to invasion by insects and decay organisms. Painting
the wound does not facilitate this process, since these treatments are no substitute for new growth rings
and in some cases actually retard the natural sealing process.
An important goal in proper pruning is to reduce the
compartmentalization response. One way to minimize and speed up the
sealing process is to minimize the size of wounds by removing undesirable
branches when they are relatively small (preferably less than 4” diameter).
This is why, with the exception of mitigating a hazardous situation,
structural pruning should be performed when trees are young and actively
growing. Additionally, it is important to always prune to a branch union,
being careful to cut just outside of the collar. The collar of a branch is
actually the outer rings of the parent branch or trunk folded back around
the base of the branch (like a towel draped around your neck). Once the
branch is removed, the collar will grow over the wound, completing the
sealing process. The branch union is also where natural intersections of
the vascular system occur, and pruning to these intersections makes it
Sealing is not complete until the
easier for the tree to “detour” the vascular energy that once flowed into the
branch collar grows completely
missing limb. Failing to preserve the branch collar by “flush cutting” or
over the wound.
allowing branches to rip off the tree substantially increases the area of
compartmentalization and severely inhibits sealing.
Every pruning cut alters the flow and distribution of energy within a tree, and understanding the basics
is necessary for anticipating and controlling pruning response. In an un-pruned branch, the terminal bud
(outermost tip) performs like a crew leader, using hormones to direct growth and keep the lateral branches
in check. Removing the terminal bud releases growth energy to the remaining lateral branches and results
in a leadership void. Pruning to the union of a lateral branch transfers the leadership role and redirects
growth into the selected lateral. Removing an entire branch transfers growth energy into the remaining
branches. The central leader (main stem) should not be cut or tipped back as this action will permanently
alter the natural shape and structure of the tree.
Pruning removes leaves. Since leaves are responsible for producing energy, removing them has an
impact on the tree’s ability to grow, protect itself from disease and pests, and even to fuel the
compartmentalization necessary to recover from the pruning event. The amount of leaf canopy that can
be safely removed depends on many factors, including the age of a tree, species, general health, and
season. A general rule of thumb is to avoid removing more than 25% of the living canopy. This is a
maximum number, not a goal to be reached, and proper pruning practices seek to minimize canopy
removal as much as possible while still correcting the structural issues.
Topping trees is never an acceptable practice. Topping
results in many open wounds with no consideration to pruning at
branch unions or collars.
The cut stubs begin to
compartmentalize, but they cannot completely seal since they are
not at a branch union and are far removed from a collar. This
leaves the stubs vulnerable to attack by insects and decay
organisms. Unfortunately, topping a tree stimulates the growth
of adventitious sprouts (multiple leafy shoots, especially on
stubs), leading to the misconception that the tree responded
favorably to the treatment. In fact, adventitious growth is an
emergency response undoubtedly developed by nature to respond
to catastrophic injuries caused by natural phenomena (e.g.,
hurricane, lightning strike, etc.). Stimulation of adventitious
growth is a sign that the tree has suffered severe damage and is
trying mightily to replace its food source. Adventitious branches
grow quickly but are poorly attached just underneath the bark (of
Topping Kills Trees!
the dying stubs), leading to hazardous conditions as the branches
become larger and heavier.
The objective of proper pruning should be the removal of crossed and competing branches as well as
dead and diseased wood and the correction of other major structural defects. Since urban trees are
destined to be part of a community, they should be trained at a young age to conform to the standards set
by the community. As with children, a properly trained tree is more likely to become a positive,
contributing member. Trees must be guided to co-exist in harmony with other components and branches
cannot be allowed to block stop signs or interfere with the normal flow of vehicular and pedestrian traffic.
Always keep in mind that pruning creates wounds, leaving the tree vulnerable to pathogen
invasion. The power to shape growth and divert energy must be used wisely and sparingly to promote
healthy structure while still preserving the natural grace and character of both the individual and the
species. In order to preserve the value and dignity of a tree, most pruning should be performed by
properly trained personnel, ideally, someone certified as an arborist or a tree worker.
For additional information and illustrations for pruning a tree
or for assistance contacting a Certified Arborist, visit www.treesaregood.com
© 2007 Tina McKeand.
Originally published in
Southwest Trees & Turf, July/August 2007.
tmckeand@davey.com
928.246.7048
Tina McKeand
Davey Resource Group
7627 Morro Rd., Atascadero, CA 93422