1. Temporal and spatial variability in stand structure and individual-tree growth for 10 years following commercial thinning in spruce-fir forests of northern Maine Christian Kuehne1, Aaron Weiskittel1, Arne Pommerening2, Robert Wagner1 1 School of Forest Resources, University of Maine 2 Department of Forest Resource Management, Swedish University of Agricultural Sciences SLU

2. All trees: spatial locations
Data
6 replicates (locations): 34- to 70-year-old naturally regenerated spruce-fir stands, not pre-commercially thinned
7 treatments: control & factorial combination of thinning method (low, dominant, or crown) and level of relative density reduction (33 or 50%)
All trees: spatial locations
10 years of annual post-treatment measurements
Permanent 0.08 ha measurement plots with a forwarder trail established in 0.37 ha treatment plots

3. Research questions
Are there differences in stand structural heterogeneity between treatments and how do they relate to variation in individual-tree diameter growth over the 10-year study period?
Do spatially explicit statistics (inclusion of tree locations) reveal new insights into the variability patterns as well as the observed stand dynamics?

4. Tree diameter distributions
(2-cm dbh classes) 1 (black) and 10 years (white bars) since thinning (YST)
Control
Crown
Dominant
Low
Change in
mean absolute ΔDBH
(cm year-1)
 YST
Control
Crown
Dominant
Low 1
0.9
1.9
1.3
2.4 10
1.1
2.6
2.9
3.0

5. DBH-based stand structural heterogeneity
quantified using the Gini coefficient 1 and 10 years since thinning (YST)
& ΔDBH-based tree growth variation
Stand structural heterogeneity
Tree growth variation
 Treatment
YST 1 10
Control
.23
.21
.72
.68
Crown
.25
.66
.51
Dominant
.17
.15
.74
.48
Low
.13
.12
.43

6. Mean pair correlation functions g(r)
& mean mark variograms 𝜸𝒎(r) for DBH
Control
Crown
Dominant
Low

7. Change in Growing Space Efficiency (GSE)
using estimated parameter a derived from nonlinear regression models
predicting GSE (mm m-2 year-1) as a function of area potentially available (APA, m2)
GSE was calculated as the ratio of annual ΔDBH (mm) and APA.
Higher a values depict greater GSE across the entire APA range.
GSE (annual ΔDBH/APA)
Treatment
Years since thinning 1 5 10
Control
0.58
0.63
0.47
Crown
0.94
2.34
1.74
Dominant
0.85
1.13
2.53
Low
1.29
1.28
0.81
GSE = a*APA^b
APA
Sit & Poulin-Costello 1994

8. Conclusions
Medium-aged suppressed and intermediate balsam fir and red spruce proved to be highly responsive to newly available growing space while growth rates in the low thinning treatments remained at relatively high levels throughout the study period
Spatially explicit statistics and measures helped to better understand observed structural and growth patterns and thus stand dynamics
Changes in forest structure and growth highlight the interrelationship of forest management, stand structure, and tree growth: permanent feedback loop

9. Thank you! Funding provided by
Northeastern States Research Cooperative
Cooperative Forestry Research Unit of Maine
German Science Foundation

10. Change in mean growth dominance G
G values greater than 0 signal growth dominance of larger trees
(i.e. contribution to stand total growth by larger trees is greater than their contribution to stand total size)
Treatment
Years since thinning 1 5 10
Control
.18
.22
.23
Crown
.17
.09
Dominant
.15
Low
-.02
.08

11. Effect of distance to forwarder trail
on relative tree species-specific diameter growth
100% = control