Ponderosa pine seedling height growth
beneath partial overstories
in the central Oregon Cascade Range
Woongsoon Jang1
Christopher R. Keyes1, David L.R. Affleck1, and Douglas A. Maguire2
1Department
of Forest Management, College of Forestry and Conservation,
University of Montana
2Department of Forest Engineering, Resources & Management,
Oregon State University
Partial overstory retention
• Compromise between timber production and ecological objectives
– 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?
Negative effects on seedling growth
• Negative relationship between seedling growth and overstory
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
Objectives
• Understand overstory/understory relationships of two-aged
ponderosa pine stands arising from dispersed variableretention 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
Study Site
Climate of study site
90
2
Precipitation
1.8
Max. Temp.
Temperature (F)
70
1.6
Min. Temp.
1.4
60
1.2
50
1
40
0.8
30
0.6
20
0.4
10
0.2
0
0
Jan
Feb
Mar Apr May Jun
Jul
Aug Sep
Oct
Nov Dec
Precipitation (in.)
80
Site description
Stand
Tree ha-1
BA
(m2 ha-1)
QMD
(cm)
Ave. Ht.
(m)
101
102
103
105
107
12
16
17
20
33
9.2
7.8
7.3
3.4
6.8
99.0
78.7
74.2
46.4
51.0
41.7
39.0
36.5
19.6
24.4
50
53
54
58
55
62
72
79
79
40
Pringle
Falls
203
204
205
206
207
208
128
39
103
192
33
80
22.5
10.8
17.3
24.3
13.9
18.1
47.4
59.3
46.3
40.2
72.8
53.7
26.0
31.7
25.5
23.1
34.2
29.8
66
44
58
54
57
50
48
77
39
9
73
54
Fort Rock
301
302
304
18
20
47
4.2
3.3
13.2
54.8
46.1
59.8
21.8
15.6
24.4
61
72
62
38
25
40
Block
Warm
Springs
Ave. LCR Shrub Cov.
(%)
(%)
Collected data
Variable Group
Parameter
Unit
Scale
Response Variable
Seedling height growth (1994-99)
cm
individual
Seedling height at 1994
cm
individual
Site index
m
plot
Planted treatment
-
plot
Site preparation
-
plot
Block
-
stand
Quadratic Mean Diameter
cm
plot
Tree density
trees ha-1
plot
Stand Density Index
-
plot
Basal Area
ft2 ac-1
plot
Vegetation Coverage
%
plot
Overhead shrub presence
-
individual
Nearest Shrub Height
cm
individual
Distance to Nearest Shrub
cm
individual
Graminoid coverage
%
plot
Potential Productivity
Overstory Retention
Understory Condition
Data analyses
• Generalized linear model (GLM)
– Random component (probability distribution)
• Gamma distribution
– Linear predictor
•
  X
– Link function
• Log transformation
•
X  ln(  )
  exp( X )
Results
Variable Group
Parameter
Est. Coeff.
S.E.
p-value
(Intercept)
-0.2792
0.1953
0.1532
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
QMD (15 m)
-0.0009
0.0005
0.0565
Tree density (15m)
-0.0055
0.0005
<0.0001
Nearest Shrub Height
0.0018
0.0003
<0.0001
Potential Productivity
Overstory Retention
Understory condition
Overstory vs. Understory
• Negative effect on seedling height growth
– 10 cm increase of QMD  0.92% reduction
• e-0.0092 = 0.9908
– Additional 10 tree/ha  5.35% reduction
• e-0.0550 = 0.9465
• Similar results with other studies and species
– Ponderosa pine (Oliver and Dolph,1992; McDonald and Abbott
1994)
– Douglas-fir (Isaac 1956; Wampler 1993; Hansen et al. 1995)
– Scots pine (Elfving and Jakobsson 2006)
Best measure of overstory?
• Basal Area (BA)
– Many study have used
• E.g. Rose and Muir 1997; Acker et al. 1998; Page et al. 2001
– Not merely a measure of aboveground competition
– Correlated with foliage or canopy coverage, root
competition, etc.
• Combination of tree density and QMD
– Account for more variance than BA
How big should the plot size be?
• Key question from competition indices
– So-called “zone of influence” (Opie 1968)
• Optimum radius of overstory plot
– Vary with tree size (Wagner and Radosevich 1991)
– 3.5 times of the mean crown radius (Lorimer 1983)
• Bigger plot explains more variance
– Beyond 18.29 m  ignorable (Hoyer 1993)
– Min. effective distance 12.19 m (McDonald 1976)
– Thus, 15 m radius is the most relevant
Shade? Or others?
• What causes the reduction of seedling growth?
– Light condition
• Influences ponderosa pine seedlings more than any other factor
• Decreases with overstory basal area increment (Oliver and Dolph 1992)
• Modifies tree attributes (Pearson 1936, Messier et al. 1999)
– Others?
• Soil moisture (McDonald and Abbot 1994)
• Competition for nutrients and low soil temperature (Lajzerowicz et al.
2004)
Prescribed burning
• Reduces fuel load, improves seedling recruitment, simulates thinning
effect, etc.
• However, the effect of prescribed burning has been debated
for a long time
• Negative effect in this study
– Loss of total biomass of duff layer
– Subsequent nutrient deficiency
• Takes long time to recover to the level of pre-burn
• Limitation of total nutrient supply (especially N)
• Delayed recovery of N-fixation shrubs
(eg. Ceanothus velutinus, Purshia tridentata)
Planting
• Already selected seedlings
– Have better geno- & phenotype
• Already grown enough to compete
• Planter could control the place to be planted
Understory veg. & seedling growth
200
150
0
50
Pringle Falls
100
Fort Rock
Height of Nearest Shrub (cm)
Height Growth
250
300
Warm Springs
FR
0
100
200
Height at 1994 (cm)
300
400
PF
Block
WS
Management implications
• Controlling seedling height growth
– Manipulation of overstory retention level
• Number and size of overstory retention trees
• Introduction of site preparation method or artificial planting
• Effects of other factors on seedling behavior
– stand history, potential productivity, and understory condition
80
60
40
20
0
QMD (cm)
100
120
140
Management implications
0
0
-1
-2
20
-3
-4
40
-5
-6
60
-7
-8
-9
-10
80
Number of trees per ha
-11
100
-12
-13
120
-14
-15
140
-16
-17
Going further…
• Spatial pattern of overstory retention?
– Palik et al. 2003; Maguire et al. 2006
• Climate?
– 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.
Cited literature
•
Acker, S.A., E. Zenner, and W. Emmingham. 1998. Structure and yield of two-aged stands on the Willamette National Forest, Oregon: implications for green tree
retention. Canadian Journal of Forest Research 28(5):749-758.
•
Hansen, A.J., S.L. Garman, J.F. Weigand, D.L. Urban, W.C. McComb, and M.G. Raphael. 1995. Alternative Silvicultural Regimes in the Pacific Northwest: Simulations of
Ecological and Economic Effects. Ecological Applications 5(3):535-554.
•
Hoyer, G.E. 1993. The influence of Douglas-fir overstory on understory tree height growth in coastal forests of Washington. Washington Department Natural Resources
Forest Land Management Research Center. Contribution No. 348.
•
Isaac, L.A. 1956. Place of partial cutting in old-growth stands of the Douglas-fir region. US Dept. of Agriculture, Forest Service, Pacific Northwest Forest and Range
Experiment Station. Research Paper 16. PNW-RP-16. p 48.
•
Lajzerowicz, C.C., M.B. Walters, M. Krasowski, and H.B. Massicotte. 2004. Light and temperature differentially colimit subalpine fir and Engelmann spruce seedling growth
in partial-cut subalpine forests. Canadian Journal of Forest Research 34(1):249-260.
•
Lorimer, C.G. 1983. Tests of age-independent competition indices for individual trees in natural hardwood stands. Forest Ecology and Management 6(4):343-360.
•
Maguire, D., D. Mainwaring, and C. Halpern. 2006. Stand dynamics after variable-retention harvesting in mature Douglas-fir forests of western North America. Allgemeine
Forst und Jagdzeitung 177(6/7):120.
•
McDonald, P.M. 1976. Inhibiting Effect of Ponderosa Pine Seed Trees on Seedling Growth. Journal of Forestry 74(4):220-224.
•
McDonald, P.M., and C.S. Abbott. 1994. Seedfall, regeneration, and seedling development in group-selection openings. U.S. Department of Agriculture, Forest Service
Research Paper PSW-RP-220. 13p.
•
Messier, C., R. Doucet, J.-C. Ruel, Y. Claveau, C. Kelly, and M.J. Lechowicz. 1999. Functional ecology of advance regeneration in relation to light in boreal forests.
Canadian Journal of Forest Research 29(6):812-823.
•
Oliver, W.W., and L.K. Dolph. 1992. Mixed-conifer seedling growth varies in response to overstory release. Forest Ecology and Management 48(1-2):179-183.
•
Opie, J.E. 1968. Predictability of Individual Tree Growth Using Various Definitions of Competing Basal Area. Forest Science 14(3):314-323.
•
Page, L.M., A.D. Cameron, and G.C. Clarke. 2001. Influence of overstorey basal area on density and growth of advance regeneration of Sitka spruce in variably thinned
stands. Forest Ecology and Management 151(1-3):25-35.
•
Palik, B., R.J. Mitchell, S. Pecot, M. Battaglia, and M. Pu. 2003. Spatial distribution of overstory retention influences resources and growth of longleaf pine seedlings.
Ecological Applications 13(3):674-686.
•
Pearson, G.A. 1936. Some Observations on the Reaction of Pine Seedlings to Shade. Ecology 17(2):270-276.
•
Rose, C.R., and P.S. Muir. 1997. Green-tree retention: consequences for timber production in forests of the western Cascades, Oregon. Ecological Applications
7(1):209-217.
•
Wagner, R.G., and S.R. Radosevich. 1991. Neighborhood predictors of interspecific competition in young Douglas-fir plantations. Canadian Journal of Forest
Research 21(6):821-828.
•
Wampler, M. 1993. Growth of Douglas-fir Under Partial Overstory Retention. M.S. thesis, University of Washington, Seattle, WA.