Relationships between forest structure, understorey light and regeneration in complex Douglas-fir dominated stands in south-eastern British Columbia Kyle Lochhead and Phil Comeau University of Alberta June 10 th, 2012

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Relationships between forest structure, understorey light and regeneration in complex Douglas-fir dominated stands in south-eastern British Columbia Kyle Lochhead and Phil Comeau University of Alberta June 10 th, 2012

Interior Douglas Fir Warm ( °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%

Structure

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

Study 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

Experimental Design CRD with subsampling 4 replicates of 4 treatments of target residual basal area (m 2 /ha): 8, 16, 24, and unharvested (~37 m 2 /ha) Regeneration growth Light measurements : LAI Plant Canopy Analzyers, Hemi-photos, Photodiodes

Structural Density Estimators N =SDI = G =SDI* = Dq =Sum Ht =

Analysis Treatment differences of DIFN, Growth: ANOVA DIFN ~ Structural density estimators: NLMM Y ij = (β 0 + u i ) e (β k X kij ) + ε ij (i = ; j = ) u i ~ N(0, σ u 2 ) ε ij ~ N(0, σ ε 2 ) 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

Understorey light availability C=H=M=L, p=0.24R 2 =0.9, RMSE = 64,079

Light availability and structure At the microsite scale adj R 2 : G (0.02) – N (0.24) Unoccupied plots predicting 31-40% full sky Separation by species SDI even ~ SDI*

Light 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.ModelAIC c ΔiΔi wiwiadj R 2 1b ( u)EXP( N layer N layer N layer P FD ) (0.280) 2b ( u)EXP( G layer G layer P FD ) (0.241) 3b ( u)EXP( SDI layer SDI layer SDI layer D q P FD ) (0.272)

Regeneration 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: R 2 : % DIFN and N best Abundance: Light is key

At 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?

Light 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 (DBH 2 ), SDI* (DBH 1.6 ), sum D (DBH 1 ) and N (DBH 0 )

Conclusions 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 m 2 /ha promote regeneration

Thank-you Funding for this research provided by B.C. Ministry of Forests and Range Assistance from Teresa Newsome and Michaela Waterhouse is gratefully acknowledged