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?