Ponderosa pine seedling height growth beneath partial overstories in the central Oregon Cascade Range Woongsoon Jang 1 Christopher R. Keyes 1 , David L.R. Affleck 1 , and Douglas A. Maguire 2 1 Department of Forest Management, College of Forestry and Conservation, University of Montana 2 Department of Forest Engineering, Resources & Management, Oregon State University
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Ponderosa pine seedling height growth beneath partial overstories in the central Oregon Cascade Range Woongsoon Jang 1 Christopher R. Keyes 1, David L.R.
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Ponderosa pine seedling height growth be-neath partial overstories in
the central Oregon Cascade RangeWoongsoon Jang1
Christopher R. Keyes1, David L.R. Affleck1, and Douglas A. Maguire2
1Department of Forest Management, College of Forestry and Con-servation, University of Montana 2Department of Forest Engineering, Resources & Management, Oregon State University
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Partial overstory retention
• Compromise between timber production and ecological objec-
tives
– Enhance structural complexity
– Increase species diversity
• Facilitating ponderosa pine seedling recruitment and survival
– Enhance seed availability
– Ameliorate environmental stressors
• For silviculturists
– Effect on growth rates of seedling?
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Negative effects on seedling growth
• Negative relationship between seedling growth and over-
story density, distance, etc.
• But, number of study is few:
– Because seedling growth prior to overstory removal was not
concerned
– Overstory retention level is constrained and retained temporary
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Objectives
• Understand overstory/understory relationships of two-
aged ponderosa pine stands arising from dispersed
variable-retention harvests
– How the growth of seedlings and saplings is influenced by
varying levels of overstory retention
– How the overstory/seedling growth relationship changes in
different environments
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Study Site
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Climate of study site
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0
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50
60
70
80
90
0
0.2
0.4
0.6
0.8
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1.6
1.8
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Precipitation
Max. Temp.
Min. Temp.
Tem
per
atu
re (
F)
Pre
cip
itat
ion
(in
.)
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Site description
Block Stand Tree ha-1 BA(m2 ha-1)
QMD(cm)
Ave. Ht.(m)
Ave. LCR(%)
Shrub Cov.(%)
WarmSprings
101102103105107
1216172033
9.27.87.33.46.8
99.078.774.246.451.0
41.739.036.519.624.4
5053545855
6272797940
PringleFalls
203204205206207208
12839
1031923380
22.510.817.324.313.918.1
47.459.346.340.272.853.7
26.031.725.523.134.229.8
664458545750
4877399
7354
Fort Rock301302304
182047
4.23.3
13.2
54.846.159.8
21.815.624.4
617262
382540
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Collected dataVariable Group Parameter Unit Scale
Response Variable Seedling height growth (1994-99) cm individual
Potential Productivity
Seedling height at 1994 cm individual
Site index m plot
Planted treatment - plot
Site preparation - plot
Block - stand
Overstory Retention
Quadratic Mean Diameter cm plot
Tree density trees ha-1 plot
Stand Density Index - plot
Basal Area ft2 ac-1 plot
Understory Condition
Vegetation Coverage % plot
Overhead shrub presence - individual
Nearest Shrub Height cm individual
Distance to Nearest Shrub cm individual
Graminoid coverage % plot
Seedling density trees ha-1 plot
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Data analyses
• Generalized linear model (GLM)
– Random component (probability distribution)
• Gamma distribution
– Linear predictor
•
– Link function
• Log transformation
•
X
)ln( X )exp( X
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Results
Variable Group Parameter Est. Coeff. S.E. p-value
(Intercept) -0.2792 0.1953 0.1532
Potential Productivity
Seedling Ht (1994) 0.6464 0.0364 <0.0001
Site index 0.0490 0.004 <0.0001
Planted treatment 0.3228 0.0419 <0.0001
Site preparation -0.2825 0.0541 <0.0001
Block (PF) 1.1249 0.18270 <0.0001
Block (WS) 0.7492 0.1741 <0.0001
Ht×(PF) -0.2341 0.0426 <0.0001
Ht×(WS) -0.0333 0.0408 0.4151
Overstory RetentionQMD (15 m) -0.0009 0.0005 0.0565
– How do seedlings respond to the weather during growing season?
• Refinement of understory veg. variables
– Plot level measurement were not appropriate
– Shrub species composition
– Interaction (e.g. competition vs. facilitation?) with seedling along
with site condition and seedling size, etc.
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