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Kyle Lochhead and Phil Comeau University of Alberta June 10 th , 2012

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. . . . . Love for the western US.

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Kyle Lochhead and Phil Comeau University of Alberta June 10 th , 2012

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  1. 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 10th, 2012

  2. . . . . Love for the western US

  3. 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 10th, 2012

  4. Interior 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%

  5. Structure

  6. 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

  7. 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

  8. Experimental 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

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

  10. Analysis • Treatment differences of DIFN, Growth: ANOVA • DIFN ~ Structural density estimators: NLMM Yij = (β0 + ui) e (βk Xkij) + εij(i = 1 .. 16; j = 1 .. 16)ui ~ N(0, σu2) 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

  11. Understorey light availability R2 =0.9, RMSE = 64,079 C=H=M=L, p=0.24

  12. Light 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*

  13. 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

  14. 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: R2: 31.9 - 63.3% DIFN and N best • Abundance: Light is key

  15. 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?

  16. 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 (DBH2), SDI* (DBH1.6), sum D (DBH1) and N (DBH0)

  17. 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 m2/ha promote regeneration

  18. 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

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