The Biology of Pruning

1. The Biology of Pruning

Bob Underwood
Dakota College at Bottineau
Underwood & Associates

2.

• Education begins when you doubt
something
• Education occurs when you resolve
your doubts.

3.

• We can not know what is wrong unless we
know what right is!!
• Diesel vs Gas Engine

4. Principles of Arboriculture

• Arboriculture 3rd and 4th Editions
• Harris, Clark, Matheny
• Prentice Hall

5. “As tree development changes with time, so must tree care”

6. With your Forest?

• The Community Tree

7. “Tree Care is a long term, low intensity process.”

8.

9. “Tree Care is founded on the principles of plant health care.”

10. AMTOP PHC

The Culprit Clean-up batter
in Nature
Bronze Birch Borer Symptom
In our yard
Nature

11. “Tree care applies general concepts to specific genotypes.”

12.

Energy - Rise and Fall
Trees are a committed
system - Like an
airplane at takeoff!!!
n
What is it used for? Where is it created?
Where is it stored?

13. Energy - Rise and Fall

• Like a Business, the Tree must make a
profit or it fails? But there are expenses!!

14. “In tree care, an ounce of prevention is worth a pound of cure because we have a limited ability to cure.”

15.

16. “Good trees and tree care start with quality plants.”

17.

18. “Tree selection is founded on ‘right plant, right place.’”

“know the place,
select the plant.”

19.

20. “Arboricultural treatments can have either positive benefits or negative consequences.”

21.

22.

23. “Tree health and hazards are related, but not equivalent.”

24.

25. “Arboriculture and Forestry are related but not equivalent fields.”

26.

27.

28. “You become responsible, forever, for what you have tamed.”

From The Little Prince

29.

30.

• Mechanical Design of Trees:
Trees as structures must develop support
tissue to not only support the combined
weight of their own components, but also
resist the forces of wind, snow, ice and
rain.

31.

• Most of the research has been done by
Claus Mattheck and his associates in
Germany. Their research is based on five
general principles.
• Trees grow to evenly distribute the stress along
their surface.
– Trees adhere to the constant stress axiom. Points where
changes in orientation occur are natural areas of
weakness, such as the outer layers of the stem, the
sapwood, which provides most of the support, except in
older trees.

32.

• Over time there are no overloaded or
under loaded points.
– Again, the constant stress axiom
applies. During severe storms there
will be areas of weakness and for a
period of time after growing conditions
around a tree have undergone radical
change, weakness may occur.
• Mechanical stress results in active
cambium growth.
– Wood production provides the support
and is fastest in a vigorous tree. Where
weakness or injury occurs, the tree
actively adds wood to repair them. We
use this fact to add girth to bonsai trees
by shaking them occasionally.

33.

• A tree's internal anatomy is directly related to
mechanical strength.
– Wood and wood rays provide the mechanical strength.
• The manner in which a tree grows reveals the
pattern of stress.
– Mattheck says, "defect symptoms are a product of
repair growth." He also says that "the body language
of trees does not tell lies."

34.

• Remember, trees grow in response to
stress. As they become larger and
heavier, the base must become bigger to
support them. This widening near the
base of the plant is referred to as taper.
• The same occurs on branches.
• If we know what causes this taper to
develop, we can train stronger trees for
the future.
• Lateral branches encourage diameter
growth and will reduce height
growth. Therefore, they should be left on
a tree when it is young to develop a
strong base, but kept under control as the
tree ages. This relatively easy, since
laterals do not grow as rapidly as upright
branches.
Cooperative Extension, College of
Agriculture & Life Sciences, The University
of Arizona

35.

Wounded or lost wood tissue is not replaced by a healing process. Wounded or lost
wood tissue is not replaced by a healing process. Perennial plants react to injury by
forming physical and chemical barriers to contain the injury and its effects. Alex Shigo
has termed this CODIT (compartmentalization of disease in trees).This is called
compartmentalization since the tree forms a compartment around the damaged area to
lessen its impact on the rest of the tree. This compartment is six sided, formed by four
walls: jury by forming physical and chemical barriers to contain the injury and its
effects. Alex Shigo has termed this CODIT .
Wall 1 - The top and bottom This is the plugging of xylem cells and tracheids above and
below the injured area. (weakest wall)
Wall 2 - The inside limit Formed by the thick walled late season cells of an interior
growth increment.
Wall 3 - The two sides The radial xylem rays running horizontally between the bark and
the interior of the tree.
Wall 4 - The outer wall The new xylem formed after the wounding takes place.
Chemically and anatomically different. (the strongest wall against spread of decay, but
structurally weak, leading to ring shakes)
Walls 2 and 3 also undergo chemical changes that produce phenols in hardwoods and
terpenes in softwoods to further limit decay.
–
–
(adapted from Shigo and Marx 1977
Photo: A.L. Shigo

36.

• Branch Attachment
• Have you ever noticed that as you pull a branch
off a tree, it only rips down, never up or
sideways? This simple observation explains quite
clearly how a branch is attached to the trunk, but
was not noticed or understood by most people
until the middle 1980's.
• This attachment point must allow for the flow of
water up to the leaves and the flow of
photosynthetic products back down, while
supporting an ever increasing mass.
• As a branch grows, it adds successive new layers
of xylem, these are in turn buried in the trunk by
the layers of xylem being formed by the
trunk. They are two distinct generating systems
and as such add another boundary to spread of
disease within the tree.
Image Source - TREES,
ASSOCIATES, and
SHIGO (2 CD set
My photo

37.

We find that if the end is broken off
a branch or a cut is made to the
cambium, buds below this point
developing into new branches will
have a more upright growth than the
norm.
If a shallow cut is made just below a
bud, again to the cambium layer, the
bud will develop a wider than normal
branch attachment.
If a lateral with a sharp angle of
attachment is removed from a young
leader, the resulting new growth
from several latent buds will have a
wider angle of attachment. With this
information we can make better
decisions on cuts when training
young trees along the street or in our
nurseries.

38.

Purposes of pruning: Before we remove a
branch from a tree, we should know exactly why
we are doing it and what the resulting action will
be on the part of the tree.
• We must know the natural form of the tree for it is
hard to fight Mother Nature.
• We must be observant so that we can determine
how a tree of unknown growth habit has
responded to the last time it was pruned and
therefore what it is likely to do in the future.

39.

The text looks at several reasons for pruning:
Training young plants,
maintenance of health and appearance,
control of plant size,
influencing flowering, fruiting and vigor,
compensation for root loss,
invigoration of stagnating plants,
and increasing the value of conifers.
While these are all standards of the industry, are
they all in the tree's best interest?

40.

• Training young plants is probably the closest to being truly beneficial
for the tree, if it reduces future need for treatment.
• If a tree has developed in its current environment, shouldn't the leaves
be of the right type to utilize light most efficiently?
• Shouldn't there be sufficient reaction wood and taper to withstand
normal winds?
• Shouldn't the tree be vigorous enough to tolerate most common
diseases and insects, eliminating the need for sprays?
• If we put the right tree in the right spot originally, why would we need
to control size?
• If the roots have been cut off, do we reduce the energy producing
component needed to replace them?
• Why do trees produce large fruit crops occasionally, fear of death?
• If we traumatically cut back a bush and it responds with a last ditch
effort to put out leaves and produce energy, have we invigorated it?
• What is vigor?

41.

• Pruning Responses:
• The initial response to pruning in most young trees and those with
few flowers is an invigoration of individual shoots (there's that i word
again) if done during the growing season.
These shoots grow longer faster and have larger leaves. The rootshoot ratio is definitely in their favor. However, this growth is later in
the season using up more reserve while creating less for storage and
the total leaf area is usually less than on an untrimmed tree.
This leads to a general dwarfing of the total plant.
If the pruning is done during the dormant season, the general dwarfing
still occurs, but the top and roots are in balance by the end of the
season and less of the obvious shoot growth is observed.
To reduce the growth rate of an individual branch, we generally
shorten it, reducing the amount of energy available for
growth. (subordination pruning)
Another concept to remember is that if we cut it to a horizontal side
branch, these grow slower than upright shoots.

42.

43.

• Time of Pruning:
• This varies from when the saw is sharp to the right time of the moon.
We
should always know the plant species, the condition it is in and what the desired
results are before we start.
Light pruning of unwanted growth can be done when it is small.
Broken and dead branches may be removed at most anytime with no effect on
plant vigor.
Generally it is best to prune deciduous trees during early dormancy, late
dormancy may lead to "bleeding" which is much more painful to the customer
than the tree.
We can pinch back tops and make small cuts to alter growth habit during the
growing season.
Another consideration is if trees are more susceptible to specific insect pests or
diseases at one time of the season or another (i.e.. Oak wilt prior to July 1 in
Red Oaks).
If you wish to slow the growth of the plants, best results will come from
pruning in late spring or early summer, reducing leaf area for the longest
period.

44.

• During the growing season, we can most easily determine
what branches are hanging too low or are dead. During
this time we may be limited by the nesting activity of
certain birds, whose presence is desired by the
homeowner.
The best general rule for flowering plants is to prune
when they finish flowering . This allows them the
necessary time to set new buds for the next season. It also
may remove the fruit before it develops and actually saves
this energy for the tree to put to other uses.
• Flowering itself does not eat into a tree’s energy reserves
to any great extent, since the energy required is already
stored in the bud or in its immediate shoot. This
characteristic makes it very hard to reduce the size of
flowers on a bonsai tree to the extent that we can the limbs
and leaves.

45.

• Closure of wounds may be faster if the pruning is done just prior or
just following initiation of growth in the spring. Within that growing
season.
• Wounds in the winter, spring or summer did not affect closure rates the
following season, however those made in the autumn slowed closure
by 20% in the first year. There was no difference in following
seasons.
• Early pruning must be done carefully since the bark may tend to slip
due to the very active cambium, and fall pruning may coincide with the
sporulation of many fungi.
Pruning may stimulate new growth if done in late fall, leading to
freeze damage. This may also occur near a pruning cut if the
temperature gets low enough. This is something to consider on some
species in colder climates.
Some trees are thinned in the fall to allow sunlight to penetrate for
residences using solar energy for part of their heating.

46.

• Did I create enough doubts to start
education??
• Now your assignment is to resolve those
doubts, between you, me and your peers.
• 701-228-2732 (your hotline to my opinions)
• Thanks as I ride off into the sunset, in my
chauffeured Limousine!!!

47.

Notes