Impact of Pruning Young Loblolly Pine Trees: Ten-year Growth Results

Ralph L. Amateis and Harold E. Burkhart

Department of Forest Resources and Environmental Conservation, Virginia Tech

Purpose: summarize growth results from two pruning studies:

• What is the impact of early pruning on height and dbh growth?

• Is it feasible to prune some of the trees in young stands?

FIELD STUDY: what is the impact of pruning on height and dbh growth?

• RCB Design: 2 locations, 4 blocks/location and 5 plots/block

• Treatment plots with six rows, six trees per row• Sixteen interior measurement trees• 10 ft x 10 ft square spacing• Planted with genetically improved seedlings• Competition control through age 2• Annual measurements of Dbh, height, and crown

dimensions

Early Tree Pruning (ETP) STUDY: How does severe pruning at young ages impact

growth?

• Control

• Prune ½ the crown at 3 yrs

• Prune ½ the crown at 6 yrs

• Prune ½ the crown at 9 yrs

• Prune ½ the crown at

3, 6, 9 yrs

Age 3 Pruning Treatment: ½ live crown length removed

Removing ½ of Live Crown Length

Age 6 Age 9

Analysis

ANOVA methods with comparisons of treatment means versus the control mean (Dunnett’s test)

Prune ½ Live

CrownYr 3

After 3rd yr

0.687

After 6th yr

0.223

After 9th yr

0.694

After 3,6,9 yr

0.911

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4

After 3rd yr

0.687 0.008

After 6th yr

0.223 0.767

After 9th yr

0.694 0.953

After 3,6,9 yr

0.911 0.002

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5

After 3rd yr

0.687 0.008 0.196

After 6th yr

0.223 0.767 0.977

After 9th yr

0.694 0.953 0.991

After 3,6,9 yr

0.911 0.002 0.264

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6

After 3rd yr

0.687 0.008 0.196 0.624

After 6th yr

0.223 0.767 0.977 0.805

After 9th yr

0.694 0.953 0.991 0.495

After 3,6,9 yr

0.911 0.002 0.264 1.000

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

PrunePrune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7

After 3rd yr

0.687 0.008 0.196 0.624 0.394

After 6th yr

0.223 0.767 0.977 0.805 0.675

After 9th yr

0.694 0.953 0.991 0.495 0.797

After 3,6,9 yr

0.911 0.002 0.264 1.000 0.698

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8

After 3rd yr

0.687 0.008 0.196 0.624 0.394 0.936

After 6th yr

0.223 0.767 0.977 0.805 0.675 0.306

After 9th yr

0.694 0.953 0.991 0.495 0.797 0.999

After 3,6,9 yr

0.911 0.002 0.264 1.000 0.698 0.595

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8 Yr 9

After 3rd yr

0.687 0.008 0.196 0.624 0.394 0.936 0.696

After 6th yr

0.223 0.767 0.977 0.805 0.675 0.306 0.073

After 9th yr

0.694 0.953 0.991 0.495 0.797 0.999 0.359

After 3,6,9 yr

0.911 0.002 0.264 1.000 0.698 0.595 1.000

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8 Yr 9 Yr 10

After 3rd yr

0.687 0.008 0.196 0.624 0.394 0.936 0.696 0.998

After 6th yr

0.223 0.767 0.977 0.805 0.675 0.306 0.073 0.899

After 9th yr

0.694 0.953 0.991 0.495 0.797 0.999 0.359 0.024

After 3,6,9 yr

0.911 0.002 0.264 1.000 0.698 0.595 1.000 0.012

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune Prune Prune

Prune ½ Live

CrownYr 3

After 3rd yr

0.980

After 6th yr

0.932

After 9th yr

0.485

After 3,6,9 yr

0.961

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4

After 3rd yr

0.980 <.0001

After 6th yr

0.932 0.467

After 9th yr

0.485 0.894

After 3,6,9 yr

0.961 <.0001

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5

After 3rd yr

0.980 <.0001 0.300

After 6th yr

0.932 0.467 0.998

After 9th yr

0.485 0.894 0.974

After 3,6,9 yr

0.961 <.0001 0.013

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6

After 3rd yr

0.980 <.0001 0.300 0.914

After 6th yr

0.932 0.467 0.998 0.999

After 9th yr

0.485 0.894 0.974 1.000

After 3,6,9 yr

0.961 <.0001 0.013 1.000

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7

After 3rd yr

0.980 <.0001 0.300 0.914 0.840

After 6th yr

0.932 0.467 0.998 0.999 <.0001

After 9th yr

0.485 0.894 0.974 1.000 0.193

After 3,6,9 yr

0.961 <.0001 0.013 1.000 <.0001

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8

After 3rd yr

0.980 <.0001 0.300 0.914 0.840 0.855

After 6th yr

0.932 0.467 0.998 0.999 <.0001 0.030

After 9th yr

0.485 0.894 0.974 1.000 0.193 0.999

After 3,6,9 yr

0.961 <.0001 0.013 1.000 <.0001 0.770

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8 Yr 9 Yr10

After 3rd yr

0.980 <.0001 0.300 0.914 0.840 0.855 0.208

After 6th yr

0.932 0.467 0.998 0.999 <.0001 0.030 0.136

After 9th yr

0.485 0.894 0.974 1.000 0.193 0.999 0.992

After 3,6,9 yr

0.961 <.0001 0.013 1.000 <.0001 0.770 1.000

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune Prune Prune

Prune ½ Live

CrownYr 3 Yr 4 Yr 5 Yr 6 Yr 7 Yr 8 Yr 9 Yr10

After 3rd yr

0.980 <.0001 0.300 0.914 0.840 0.855 0.208 0.670

After 6th yr

0.932 0.467 0.998 0.999 <.0001 0.030 0.136 0.896

After 9th yr

0.485 0.894 0.974 1.000 0.193 0.999 0.992 <.0001

After 3,6,9 yr

0.961 <.0001 0.013 1.000 <.0001 0.770 1.000 <.0001

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune Prune Prune

Cumulative Height

0

5

10

15

20

25

30

35

40

3 4 5 6 7 8 9 10

Age

He

igh

t (f

t)

Control

Age 3

Age 6

Age 9

Age 3,6,9

Cumulative Dbh

0

1

2

3

4

5

6

7

3 4 5 6 7 8 9 10

Age

Db

h (

in)

Control

Age 3

Age 6

Age 9

Age 3,6,9

After 10 years:

•Height: Only age 3-6-9 lift treatment is shorter than control.

•Dbh: Only age 6 lift and the age 3-6-9 lift treatment have smaller Dbh than control.

Another question regarding pruning:

• Is it feasible to prune some of the trees in a loblolly pine stand?

FIELD STUDY

• RCB Design: 2 locations, 4 blocks/location and 5 plots/block

• Treatment plots with eight rows, eight trees/row• Thirty-six interior measurement trees• 6 ft x 6 ft square spacing• Planted with genetically improved seedlings• Competition control through age 2• Annual measurements of Dbh, height, crown

dimensions

Some Tree Pruning (STP) STUDY: Is it feasible to prune some of the trees in a stand?

Treatments After Year 6

• Control

• Prune 25% of the live crown length on all the trees

• Prune 50% of the live crown length on all the trees

• Prune 25 % of the live crown length on ½ the trees

• Prune 50% of the live crown length on ½ the trees

Scheme for systematically pruning ½ the trees on a plot

Control Plot at Age 6

Age 6 Pruning Treatments

Remove ¼ crown on all trees

Remove ¼ crown on every other tree

Remove 1/2 crown on every other tree

Remove 1/2 crown on all trees

Treatment Yr 5 Yr 6 Yr 7 Yr 8 Yr 9 Yr 10

Prune ¼ crown on all trees

0.996 0.999 0.999 0.987 0.986 0.826

Prune ½ crown on all trees

0.601 0.978 0.850 0.005 0.913 0.509

Prune ¼ crown on

some trees0.953 0.691 0.981 0.999 0.914 0.331

Prune ½ crown on

some trees0.297 0.585 0.837 0.035 0.954 0.158

Adj. P-values for Height Growth: Treatment Plots vs Control Plot

Prune

Treatment Yr 5 Yr 6 Yr 7 Yr 8

Prune ¼ crown all

trees0.934 0.852 0.097 1.000

Prune ½ crown all

trees0.374 0.999 <.0001 0.090

Prune ¼ crown on

some trees1.000 0.461 0.582 0.999

Prune ½ crown on

some trees0.171 0.996 0.001 0.326

Adj. P-values for Dbh Growth: Treatment Plots vs Control Plot

Prune

Treatment Yr 6 Yr 7 Yr 8 Yr 9

Prune ¼ crown ½ trees

18 Unpruned trees

18 Pruned trees

0.859

0.849

0.953

1.000

1.000

0.992

1.000

0.310

Prune ½ crown ½ trees

18 Unpruned trees

18 Pruned trees

0.735

0.807

1.000

0.551

0.554

0.015

0.997

0.548

Adj. P-values for Height Growth: Plots Where Some of the Trees are Pruned vs Control Plot

Treatment Yr 6 Yr 7 Yr 8 Yr 9

Prune ¼ crown ½ trees

18 Unpruned trees

18 Pruned trees

0.820

0.569

1.000

0.198

0.980

1.000

0.973

0.974

Prune ½ crown ½ trees

18 Unpruned trees

18 Pruned trees

0.998

1.000

0.531

<.0001

0.985

0.018

0.967

1.000

Adj. P-values for Dbh Growth: Plots Where Some of the Trees are Pruned vs Control Plot

After 10 years:

•Height: No impact on height development

•Dbh: Only heavily pruned trees with unpruned neighbors exhibit reduced Dbh growth

Cumulative Dbh

3

3.5

4

4.5

5

5.5

6 7 8 9 10

Age

Db

h (

in)

Control Prune 1/4 crown Prune 1/2 crown

Prune 1/4 crown no Prune 1/4 crown yes Prune 1/2 crown no

Prune 1/2 crown yes

Cumulative Height

1517192123252729313335

6 7 8 9 10

Age

Hei

gh

t (f

t)

Control Prune 1/4 crown Prune 1/2 crown

Prune 1/4 crown no Prune 1/4 crown yes Prune 1/2 crown no

Prune 1/2 crown yes

Overall Conclusions

• Light pruning affects neither height nor diameter.

• Following severe pruning, height growth of pruned trees is little affected even where neighbors remain unpruned; diameter growth is more negatively impacted than height growth.

• Pruning some of the trees in a stand does not improve the growth of neighboring unpruned trees.

• Growth recovery occurs quickly following pruning.

• Pruning treatments employing multiple lifts negatively impacts height and diameter.

Questions?