Effects of Thinning on Production of Dead Trees and Stand Structure
Michael Pollock, NOAA-NWFSCThomas Spies, Forest Service, PNW Research
With special thanks to:Rob Pabst, Oregon State University
Stuart Johnston, Siuslaw NF
What are the effects of thinning in plantations?
• Dead tree production following thinning• Size of future dead and live trees• Different thinning prescriptions including no
thinning• Different stand simulation models
What do different stand densities look like?
60 tpa (150 tpha)
100 tpa (247 tpha)
225 TPA (555 tpha)
Courtesy Stu Johnston
Effects of Thinning on Forest Structure
Distribution of stand densities, before (circles) and after (triangles) restoration treatment
10 20 30 40 50 60 700
200
400
600
800
1000
1200
DBH (cm)
Tree
s per
Hec
tare
(TPH
)
Grey squares are stands modeled
Note that no high density stands were modeled
0 50 100 150 200 2500
20
40
60
80
100
120
140
160
Reference StandsIndividual Modeled StandsAverage of Modeled Stands
Stand Age (Yr)
Aver
age
DBH
(cm
)
0 50 100 150 200 2500
10
20
30
40
50
60
70
80
Reference StandsIndividual Modeled StandsAverage of Modeled Stands
Stand Age (Yr)
Aver
age
Ht (m
)
0 50 100 150 200 2500
100
200
300
400
500
600
Reference Stands
Individual Modeled Stands
Average of Modeled Stands
Stand Age (Year)
LTPH
-Sta
nd
Model calibration against reference
stands
Effects of thinning on mortality rates
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 2000
10
20
30
40
50
60
70
80Mortality Rates
NTC > 50 cm
400 TPH thin > 50 cm
250 TPH thin > 50 cm
150 TPH thin > 50 cm
NTC > 30 cm
400 TPH thin > 30 cm
250 TPH thin > 30 cm
150 TPH thin > 30 cm
Year post thinning
Larg
e Di
amet
er M
orta
lity
(TPH
) Peak mortality (dead wood production) occurs early in forest development
Effects of thinning on mortality, trees > 50 and > 100 cm dbh
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 2000
50
100
150
200
250
300Cumulative Mortality NTC > 50 cm
400 TPH thin > 50 cm250 TPH thin > 50 cm150 TPH thin > 50 cmNTC > 100 cm400 TPH thin > 100 cm250 TPH thin > 100 cm150 TPH thin > 100 cm
Year post thinning
Cum
ulati
ve La
rge
Diam
eter
Mor
talit
y (T
PH)
196 for NTC vs. 90 for 150 TPH thin
Effects of thinning on live trees, > 50, 100 and 150 cm dbh
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 2000
20
40
60
80
100
120
140 Live Trees, 50, 100 & 150 cmNTC > 50 cm400 TPH thin > 50 cm250 TPH thin > 50 cm150 TPH thin > 50 cmNTC > 100 cm400 TPH thin > 100 cm250 TPH thin > 100 cm150 TPH thin > 100 cmNTC > 150 cm 400 TPH thin > 150 cm250 TPH thin > 150 cm150 TPH Thin > 150 cm
Year post thinning
Larg
e Di
amet
er Li
ve T
rees
(TP
H)
89 for NTC vs. 55 for 150 TPH thin
34 for 150 TPH thin vs. 18 for NTC
99 for 150 TPH thin vs. 78 for
NTC
“Functional” sizes of snags
Unconventional Thinning Accelerate Wood Recruitment
Leave some or all of tree boles in riparian area for ecological objectives
100 TPA
Can accelerate production and accumulation of dead trees by many timesover unthinned stand during the first 50 years
Effect mainly for trees < 20 inches dbh
Cumulative Dead Tree Production for Thinning Prescriptions that Leave Dead Trees
10-20 “ DBH 20-40” DBH
> 40 “ DBH
10-20”No Thin~280 tpa
10-20”Thin to 90 tpa
Comparison of Organon, FVS and ZELIG stand models
Comparison of Organon, FVS and ZELIG stand models
20-40”No Thin~280 tpa
20-40”Thin to 90 tpa
Very Large Snags > 40” dbh
Conclusions
• Conventional thinning generally produces fewer large dead trees compared to unthinned stands
• Conventional thinning can accelerate development of very large dead trees by 1-20 years
• Thinning that leaves some or all of the dead wood can more rapidly produce dead trees compared with unthinned stands
• Assessments of thinning effects may vary depending on the stand model used
“Functional” sizes of live trees