establishment of the paired-plot density management
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Mark Coleman, Terry Shaw & Mark Kimsey
Establishment of the Paired-Plot Density
Management network: 2013-2018
Goal: Improving vigor and adding value to managed
forests of the diverse Inland Northwest landscape.
IFC Goal & Membership
Obvious need to test site-specific silvicultural options in the INW
Wie et al 2018
Categorize forest site quality throughout the Inland Northwest
• Define tree and stand responses to treatments across the range of forest site conditions
• First focused on site factors that define maximum stand density
• Density management creates lasting improvements to stand condition
Utility of Density Management
• Improves stand structure and development through density management
• Enhances resistance to fire, drought, pests & disease
Forgone or delayed thinning :
• Growth opportunity loss
• Extends rotation
• Increases mortality risk
Stand density relative to normal stands defines
thinning prescriptions for highest stand vigor
ln Density
ln D
iam
eter
100% - Normal60% - Eminent mortality35% - Lower Management Zone25% - Crown closure
Self-thinning
trajectory
Density Management Research
1. Carrying capacity analysis• Characterize maximum density across the INW
• Species specific
2. Spacing Trials• Validate maximum density models
• Compare growth response to thinning among site classes
• Determine how stand development affects thinning response
Kimsey et al 2019
Geospatial representation of maximum Stand Density Index
Maximum density frontier models
TopographyGeography
ClimateSoil
Density x Diameterdepends on:
Spacing Trials
• Identify how stage of stand development affects thinning response
• Measure thinning response across site productivity classes
• Compare among dominate species
Total stand productivity should reach a broad optimum following canopy closure
Growth phases:
I.No competition
II.Growth decline
III.Constant wide optimum
IV.Competition-caused decline
Langsaeter’s Curve
Δ𝐺
Δ𝐺𝑆=⇩
Δ𝐺
Δ𝐺𝑆= 0
Δ𝐺
Δ𝐺𝑆< 0
To plateau or not to plateau
• Uncertain width of plateau
• Uncertain effect of site quality
• Gross vs Net production
• Typically noisy data causes uncertainty
Sta
nd
Pro
du
ctivity
Relative Density
Moderate optimum
Continuous increase
0 25 50 75
Growing stock
Gro
wth
Loblolly pineBurkhart 2005
Broad optimum
Sta
nd
Pro
du
ctivity
Site ClassT
ree
Gro
wth
Site Class
No-thin
Thin
Site class vs. growth
• Stand growth of thinned stands may exceed that of no-thin on high sites
• Growth of thinned trees will always exceed no-thin trees; difference may be greatest on high sites
No-thin
Thin
Paired Plot Density Management (PPDM)Objectives
1. Describe growth-density function shape
2. Identify optimal time of thinning for small diameter stands
3. Evaluate site effects on thinning response
4. Thinning effects on light, water, and nutrients
Thinning operations throughout
the Inland Northwest
• 4 site classes x 3 density
classes
• Divided among three forest
types
101 PPDM study
locations
Site Productivity Class
Density 1 2 3 4
I 1 13 13 8
II 10 15 16 4
III 2 8 9 2
Site productivity10-yr increment estimates
DF PP WL
Minimum 15 10 20
25th 19 14 22
mean 23 18 25
75th 26 23 27
Maximum 31 27 30
Matrix grid evenly classified site conditions
• Corners were hard to fill
• High density larch not available
• Represents range of forest stand conditions
0
2 5
5 0
7 5
1 0 0D F
15 19 23 27 31
0
2 5
5 0
7 5
1 0 0
P P
Cu
rti
s'
Re
lati
ve
De
ns
ity
10 14 18 2723
0
2 5
5 0
7 5
1 0 0W L
T e n -ye a r H e ig h t G ro w th
20 22 25 27 30
PPDM within site plotDesign
• 3-4 plots at each location
• No-thin
• Operational thin
• Alternative thin
4.3 m 14 foot
5.5 m 18 foot
No thin, Control
Light to moderate thin, 10-14 foot
Moderate to heavy thin, 16-18 foot
Establishment results
• Stand structure
• Density distribution
• Dependent site factors
Structure modified by thinning
• Removal of ingrowth
• Shift mean diameter right
2 4 6 810
12
14
16
0
2 0 0
4 0 0
6 0 0
8 0 0D o u g la s - f ir
Tre
es
pe
r A
cre
D F T h in
D F N o th in
2 4 6 810
12
14
16
0
2 0 0
4 0 0
6 0 0
8 0 0 P o n d e ro s a p in e
D ia m e te r c la s s ( in )
2 4 6 810
12
14
16
0
2 0 0
4 0 0
6 0 0
8 0 0W e s te r n L a rc h
DF examples
Site 2Den 2
Site 4Den 1
Site 1Den 2
Site 2Den 2
Site 3Den 3
Site 4Den 3
Composition modified by thinning
• Increased composition of target species to almost 90%
• Little additional effect between spacing levels
• PP was less affected than others N
on
e
Lig
ht
Mo
dera
te
0
2 0
4 0
6 0
8 0
1 0 0
D o u g la s - f ir
Sp
ec
ies
Co
mp
os
itio
n (
%)
No
ne
Lig
ht
Mo
dera
te
0
2 0
4 0
6 0
8 0
1 0 0
W e s te r n L a rc h
D F
G F
W L
L P
P P
O th e r
T h in n in g T re a tm e n t
Stand metrics among experimental factors
• Basal Area
• Reflects experimental design
• Increases with density class in no-thin plots
• Decreases with thinning
• BA is not affected by productivity class
I I I I II
0
5 0
1 0 0
1 5 0
2 0 0
D e n s ity C la s s
Ba
sa
l a
re
a
(ft
2 a
c-1
)
N one
L ig h t
M o d e ra te
Stand metrics among experimental factors
• Stand Densityi.e. Curtis’ RD
• Increases with density class
• Thinning decreases density
• RD is not affected by site productivity class
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity I N one
L ig h t
M o d e ra te
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity II
Cu
rti
s'
Re
lati
ve
De
ns
ity
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity III
S ite P ro d u c tiv ity C la s s
Stand metrics among experimental factors
• Stand Densityi.e. Portion of SDImax
• Increases with density class
• Thinning decreases density
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity I N one
L ig h t
M o d e ra te
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity II
Pe
rc
en
t o
f M
ax
imu
m
Sta
nd
De
ns
ity
In
de
x
1 2 3 4
0
5 0
1 0 0
1 5 0
D e n s ity III
S ite P ro d u c tiv ity C la s s
Comparison among density metrics
0 1 2 3 4 5
0
2
4
6
ln C u rt is ' R e la tiv e D e n s ity
ln P
erc
en
t o
f M
ax
imu
m
Sta
nd
De
ns
ity
In
de
x
D F
W L
P P
0 5 0 1 0 0 1 5 0
-1 0 0
-5 0
0
5 0
1 0 0
R e s id u a ls : L in e a r re g . o f % S D Im a x v s R D
D E N S IT Y 0
Re
sid
ua
ls
D F
W L
P P
Stand metrics among experimental factors
• Diameter
• Low in stand density class I
• Thinning increases mean diameter, thinning from below
1 2 3 4
0
2
4
6
8
1 0
1 2
D e n s ity I N one
L ig h t
M o d e ra te
1 2 3 4
0
2
4
6
8
1 0
1 2
D e n s ity II
Qu
ad
ra
tic
Me
an
Dia
me
ter (
in)
1 2 3 4
0
2
4
6
8
1 0
1 2
D e n s ity III
S ite P ro d u c tiv ity C la s s
Ten-year Site Productivity explained by Climate and Topography
• Moisture
• Temperature
2 .0 2 .5 3 .0 3 .5 4 .0
0
6
7
8
9
1 0
ln E
lev
ati
on
(ft
)
r2
= 0 .2 1
2 .0 2 .5 3 .0 3 .5 4 .0
0 .0
0 .5
1 .0
1 .5
2 .0
ln A
nn
ua
l D
ry
ne
ss
In
de
x
r2
= 0 .1 7
2 .0 2 .5 3 .0 3 .5 4 .0
0
2
3
4
5
6
ln F
ro
st-
Fre
e P
erio
d (
d)
r2
= 0 .2 3
2 .0 2 .5 3 .0 3 .5 4 .0
0
3
6
7
8
ln D
eg
re
e D
ay
s >
5o
C
r2
= 0 .0 7
ln T e n - y e a r H e ig h t G r o w t h
PPDM Establishment Summary
• Rotation-long study designed to validate SDImax estimates
• Addresses where and when to most effectively thin stands
• Includes full range of productivity and stand densities
• Data analyzed through regression analysis or with analysis of variance
• Plot network will serve many purposes
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