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![[photo] Mechanical thinning treatment](../img/mechanical_thin_tn.jpg) |
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Mechanical
thinning
treatment.
(E.
Sagor) |
Foresters
manage
stands
to meet
a variety
of landowner
objectives.
In cases
where
timber
production
is the
primary
objective,
management
often
focuses
on maximizing
financial
return.
This usually
involves
encouraging
growth
on some
collection
of desirable
trees,
while
capturing
mortality
from the
less vigorous
ones.
Density
control
is the
primary
means
by which
this is
accomplished.
There
are a
number
of thinning
methods
which
can be
used over
the life
of a stand.
A few
of the
methods
often
used in
even-aged
red pine
management
include
mechanical
thinning
and thinning
from below.
Mechanical
thinning
is the
removal
of trees
in rows
or strips
at fixed
spacing
intervals
throughout
the stand.
This method
is commonly
applied
as the
first
thinning
in red
pine stands
that are
densely
crowded
and have
a relatively
uniform
crown
class.
Typically
every
second
or third
row is
removed
until
the stand
matures
and most
of the
remaining
trees
are large,
high quality
growing
stock.
At this
point,
row thinning
becomes
less suitable
and thinning
from below
becomes
the more
appropriate
thinning
method.
Thinning
from below
is the
removal
of intermediate
and codominant
trees
to favor
the large,
high quality
trees
in the
upper
crown
classes.
Depending
on the
users
objectives
the trees
removed
during
low thinnings
are typically
high risk
trees,
trees
that are
crowding
potential
crop trees,
undesirable
species
and trees
of poor
quality
and low
vigor.
As a general
rule, high
quality
leave trees
which will
be used
as a seed
source
should be
disease
free, with
straight
stems,
medium to
thin branches
that meet
the trunk
at a 90
degree
angle, are
good self-pruners,
and possess
a crown
balanced
in height
and width.
For timber
purposes,
avoid leaving
trees with
large diameter
branches
that may
not be
able to
support
snow loads
and those
with forked
stems and
irregular
or misshapen
crowns.
![[graphic] Row thinning illustration](../img/rowthin.gif)
Two
important
aspects
of stand
density
in even-aged
stands
are
stocking
level
and
uniformity.
As the
stocking
level
decreases
towards
a minimum,
uniformity
of distribution
of trees
increases
in
importance.
The
minimum
stocking
level
for
uniform
stands
of different
(average)
stand
diameters
was
calculated
using
the
maximum
amount
of growing
space
required
by trees
of different
diameters
(stocking
chart).
Minimum
stocking
for
stands
averaging
5
inches
in
diameter
is
about
400
trees
and
60
squre
feet
per
acre.
In
stands
averaging
15
inches
in
diameter,
minimum
stocking
is
about
80
trees
and
100
square
feet
per
acre.
The stocking chart suggests
the recommended
upper
limit
of stocking
for managed
stands
averaging
5 inches
in diameter
is about
1100
trees
and 150
square
feet
per
acre
of basal
area.
For stands
averaging
15 inches
in diameter,
the recommended
upper
limit
of stocking
is 175
trees
and 215
square
feet
per
acre
of basal
area.
Contemporary
management
entails
lower
planting
densities,
plant
equipment
considerations,
and access
for pre-commercial
thinnings.
Seedling and sapling stands (less than 5 inches average diameter) should have between 400 and 900 trees per acre. Fewer than 400 trees will not provide minimum recommended stocking by the time the stand reaches pole-timber size and more than 900 trees will exceed the upper limit of recommended stocking before the trees reach pole-timber size and can be thinned commercially.
Stand
density
guides
for uneven-aged
red pine
stands
have
not been
formalized
but in
general,
seedling
density
needs
to be
higher
than
sapling
density,
which
in turn
needs
to be
higher
than
pole density,
which
should
outnumber
sawtimber
density.
Losses
in the
smaller
size
classes
are expected
and considerable
effort
will
be needed
to assure
survival
and growth
of enough
trees
in each
class
to replace
those
harvested,
lost,
or which
have
recruited
into
the next
size
class.
The regeneration
in uneven-aged
red pine
stands
must
be monitored
for Sphaeropisis
and Sirococcus
shoot
blights.
Precommercial
Thinning: Precommercial
thinning
may
be
needed
in
young
stands
to
meet
management
objectives.
For
example,
in
a
naturally-regenerated
stand
of seedlings
(less
than
2
inches
average
diameter)
having
more
than
2000
trees
per
acre,
a
minimum
of
100
potential
crop
trees
per
acre
should
be
given
a
minimum
growing
space
of
25
square
feet per
tree.
Densely
stocked
saplings
stands
(2
to
5
inches
average
diameter)
with
a
basal
area
of
160
square
feet
per
acre
or
more
should
be
precommercially
thinned.
Crop
trees
in
sapling
stands
should
be
given
about
50
square
feet
of
growing
space
per
tree
to
maintain
good
diameter
growth.
Commercial
Thinning: One
of
the
most
important
ways
stand
composition
and
development
can
be
controlled
is
by
periodic
commercial
thinnings.
Stands
should
be
thinned
before
they
exceed
the
recommended
upper
limit
of
stocking
for
managed
stands
(see
below).
For
production
management,
a
uniform
distribution
of
high
quality
trees
with
at
least
the
minimum
recommended
stocking
for
the
average
stand
diameter
should
be
left,
but
not
over
half – and
preferably
less – of
the
basal
area
should
be
removed
in
any
one
thinning.
Stands
managed
near
the
minimum
recommended
stocking
will
have
the
most
rapid
diameter
growth.
As
a
more
general
guide,
pole
stands
(5
to
9
inches
average
diameter)
should
be
considered
for
thinning
when
the
basal
area
is
140
square
feet
or
more
per
acre
and
they
should
be
thinned
to
leave
about
90-110
square
feet
per
acre.
Stocking charts and Density Management Diagrams (DMDs) are popular tools for developing thinning prescriptions for even-aged stands. Their popularity stems from their ability to easily incorporate the ecological principle of self-thinning, or competition induced mortality, which provides the stimulus for thinning. The focus of management in the context of density control is to prevent stands from reaching the zone where self-thinning can occur.
On the stocking chart self-thinning would occur when stands reach the A-line. Basal area is represented by the “Y” axis and trees per acre are represented by the “X” axis. Average stand diameter at breast height is represented by the lines radiating out from the origin of the two axes. Red pine stands are over-stocked above the A line – too high of a basal area, too many trees per acre, and too big. The stand is under-stocked below the B line – too few trees of any size.
Stocking charts and DMDs are similar management tools; their primary difference being the scale of measurement. DMDs use a logarithmic scale. A density management diagram for red pine and instruction for its usage.
Thinning
will
not usually
result
in an
increase
in stand
volume
at the
end of
the rotation.
Rather,
thinning
will
allow
individual
trees
to grow
larger
and increase
the relative
rate
of stand
growth.
Thinned
volume
plus
volume
at the
end of
the rotation
(total
yield)
may or
may not
be higher
than
the total
volume
of an
unthinned
stand.
Thinning,
however,
serves
to capture
volume
otherwise
lost
to mortality.
Thus,
total
volume
removed
over
the life
of a
stand
may be
greater
if a
thinning
program
is implemented.
Site
quality,
thinning
intensity,
and stand
age at
thinning
are factors
that
affect
volume
removed
during
thinning
and stand
volume
at the
end of
a rotation.
Residual
trees
should
have
a live
crown
ratio
of 30%
or greater
in order
to receive
the maximum
potential
growth
response
from
thinning.
Many
organizations
are emphasizing
a 40%
live
crown
ratio.
Depending
on stand
age,
trees
with shorter
live
crown
ratios
may have
a minimal
growth
response
from
thinning.
Red pine
crowns
develop
upward
and outward.
Thus,
if a
stand
is near
its
maximum
potential
height
and
has a
10% live
crown
ratio,
very
little
growth
response
to thinning
would
be observed.
For
red pine,
post-thinning
stand
density
has
a greater
impact
on post-thinning
stand
growth
(Gilmore
et al.
2005)
than
the
thinning
method
used
(Smith
2003).
For income focused management, sawtimber trees should be thinned periodically to maintain uniform growth rates on the crop trees. For habitat focused management in mixed-species stands, red pine might be favored as crop trees at each thinning. However, other species should be left to achieve biodiversity goals, provide habitat requirements, and expand the species and type of timber products.
Insect
and
disease
Warning
From
a pest
management
standpoint,
thinning
is viewed
as very
beneficial.
It generally
maintains
or increases
individual
tree health
and vigor.
Vigorous
pine trees
can better
defend
themselves
from most
insect
and disease
problems.
However,
the presence
of many
freshly
cut stumps
and logs
can, on
occasion,
attract
or provide
conditions
suitable
for some
significant
pests.
- Annosum
root
disease can
be
introduced
into
stands
through
fresh
stumps.
This
disease
causes
expanding
pockets
of
dead
and
dying
pine.
Annosum
is
present
in
lower
Michigan
and
it
has
been
expanding
in
Wisconsin.
It
is
likely
to
be
found
relatively
soon
in
Minnesota
red
pine.
The
link
above
provides
detailed
management
recommendations
that
can
reduce
the
likelihood
of
introducing
or
spreading
Annosum.
- Freshly
cut
logs
left
in
a stand
in
the
spring
and
early
summer
can
provide
breeding
material
that
produces
large Ips bark
beetle populations.
Population
increases
of
10-fold
can
occur
in
one
growing
season,
with
three
generations
of Ips
pini possible.
Thus,
a
local
population
of
1,000
can
increase
to
1,000,000
individuals
in
one
season.
Management
suggestions
revolve
around
prompt
removal
of
freshly
cut
logs
in
spring
and
summer.
This
includes
removal
in
the
early
spring
of
logs
cut
during
the
winter
months.