Effects of Thinning on Production of Dead Trees and Stand Structure

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 cm NTC > 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