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Kyle Lochhead and Phil Comeau University of Alberta June 10 th , 2012
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Transcript of Kyle Lochhead and Phil Comeau University of Alberta June 10 th , 2012
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Relationships between forest Relationships between forest structure, understorey light and structure, understorey light and
regeneration in complex Douglas-fir regeneration in complex Douglas-fir dominated stands in south-eastern dominated stands in south-eastern
British ColumbiaBritish Columbia
Kyle Lochhead and Phil ComeauUniversity of Alberta
June 10th, 2012
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. . . . Love for the western US
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Relationships between forest Relationships between forest structure, understorey light and structure, understorey light and
regeneration in complex Douglas-fir regeneration in complex Douglas-fir dominated stands in south-eastern dominated stands in south-eastern
British ColumbiaBritish Columbia
Kyle Lochhead and Phil ComeauUniversity of Alberta
June 10th, 2012
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Interior Douglas FirInterior Douglas Fir• Warm (1.6 - 9.5°C) and
Dry (300 – 750 mm)
• Fd – Lw – Pl
• Fire dominated
• Large openings – Frost
• Mule deer
• Light requirements of Fd (coast); >20% survive, morphology < 40%; Fd (interior) found in 5%
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StructureStructure
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Characterizing light levels in the understory
• Many studies indicate that stand characteristics such as basal area (Hale 2003), SDI (Vales and Bunnell 1988), Relative Density (Comeau and Heineman 2003) can be used to predict light levels
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Study SiteStudy Site
• IDFdm2• Mixed conifer
– Fd, Lw, Pl, PP
• Fire occurred 120 yrs– Lw is over 200 yrs
• Harvested in 1994• Selection harvesting
with differing residual basal areas
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Experimental DesignExperimental Design
• CRD with subsampling• 4 replicates of 4 treatments
of target residual basal area (m2/ha): 8, 16, 24, and unharvested (~37 m2/ha)
• Regeneration growth• Light measurements : LAI-
2000 Plant Canopy Analzyers, Hemi-photos, Photodiodes
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Structural Density EstimatorsStructural Density Estimators
𝜋൬𝑑𝑖200൰2
𝑁൬𝐷𝑞25൰1.6
ඨσ(𝑑𝑖2) 𝑛
𝑁𝑖൬Di25൰1.6
𝑛𝑖 N = SDI =
G = SDI* =
Dq = 𝐻𝑡𝑖 Sum Ht =
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AnalysisAnalysis
• Treatment differences of DIFN, Growth: ANOVA
• DIFN ~ Structural density estimators: NLMM
Yij = (β0 + ui) e (βk X
kij) + εij (i = 1 .. 16; j = 1 .. 16) ui ~ N(0, σu
2)
εij ~ N(0, σε2)
• Combination- backwards: AIC
• Species specific (Fd, Lw, Pl), Size effects of Layers: 1 (>12 cm dbh), 2 (7.5 – 12 cm dbh), 3 (4-7.5 cm
dbh): compare parameter estimates
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Understorey light availabilityUnderstorey light availability
DIFN
Tota
l PPF
D (µ
mol
/m²)
0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
0e+0
01e
+05
2e+0
53e
+05
4e+0
55e
+05
6e+0
5
CH
LM
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Diffuse Non-interceptance
Trea
tmen
t
C=H=M=L, p=0.24R2 =0.9, RMSE = 64,079
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0.0 0.2 0.4 0.6 0.8 1.0
0.1
0.3
0.5
0.7
G (m²/0.01ha)
DIF
N
0 10 20 30 40
0.1
0.3
0.5
0.7
N (Trees/0.01ha)
DIF
N
0 5 10 15
0.1
0.3
0.5
0.7
SDIeven/0.01ha
DIF
N
0 5 10 15
0.1
0.3
0.5
0.7
SDI*/0.01ha
DIF
N0 20 40 60 80
0.1
0.3
0.5
0.7
Sum log(DBH)/0.01ha
DIF
N
0 100 200 300 400
0.1
0.3
0.5
0.7
Sum Height/0.01haD
IFN
Light availability and structureLight availability and structure
• At the microsite scale
adjR2: G - 0.37 (0.02) – N - 0.54 (0.24)
• Unoccupied plots predicting 31-40% full sky
•Separation by species
•SDIeven ~ SDI*
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Light availability and structureLight availability and structure• Combination of structural variables was marginal – issues
with multicollinearity • Dq positively related to DIFN, Skewness coefficients• Layer 1 (>12 cm) was not significant, Layer 2 (7.5-12) and
3 (4 – 7.5) not different
No. Model AICc Δi wi adjR2
1b(0.4509+ u)EXP(-0.02785 Nlayer1 -0.04504 Nlayer2 -0.0189
Nlayer3 - 0.2673 PFD)-548.2 4.8 0.073
0.547 (0.280)
2b (0.3823+ u)EXP(-6.2917 Glayer2-11.7093 Glayer3-0.1605 PFD) -538.3 14.7 0.0010.525
(0.241)
3b(0.3704+ u)EXP(-0.02424 SDIlayer1-0.1886 SDIlayer2-0.2370
SDIlayer3+ 0.005996 Dq -0.1868 PFD)-543.1 9.9 0.006
0.541(0.272)
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RegenerationRegeneration
• Height growth is slow (<20% fully sky)– 2.3 to 6.8 cm
• Treatment differences– Small (p=0.47), Medium (p =
0.56), Large (p = 0.36)
• Average 5 year leader length: R2: 31.9 - 63.3% DIFN and N best
• Abundance: Light is key
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At the microsite-scaleAt the microsite-scale
• Structural estimators capture < 55 (28)% – Measuring diffuse light– Small plot sizes (40% full sky in open plots)– Spatial information
• Covariates – non collinear, Dq positively related to light
• Effect of small trees (i) per unit basal area MAY have greater leaf area (ii) crowns closer to measurement point (iii) clumps
• How does this fit in with size-density relationships?
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Light and size-densityLight and size-density
• Uneven-aged – Dq can range with the same N, estimate of skewness is needed
• SDI* deals with skewness and assumes additively but in this empirical study proved similar to SDI– Truncation of smaller classes (Ducey 2009)
• Sterba and Monserud (1993) – Flatter slope– This slope is not constant- often curvi-linear, other factors
• At the microsite - individual weight G (DBH2), SDI* (DBH1.6), sum D (DBH1) and N (DBH0)
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ConclusionsConclusions
• Light availability is variable at the microsite
• The linkage between management at the stand level and microsite level– Use a growth model or … use bigger plots,
include spatial info, size-density relationships with structure
• RBA below 24 m2/ha promote regeneration
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Thank-you
Funding for this research provided by B.C. Ministry of Forests and RangeAssistance from Teresa Newsome and Michaela Waterhouse is gratefully acknowledged