Phil Comeau*, Gary Kerr, Sophie Hale and Arne Pommerening

Transcription

1 Effects of levels of overstory retention on understory light and implications for regeneration in Britain and western Canada Phil Comeau*, Gary Kerr, Sophie Hale and Arne Pommerening *Univ. of Alberta, Edmonton, AB, Canada

2 Major Factors influencing Ss and Fd regeneration establishment and survival in Britain and Canada In UK SS 7 ha (49% of forest cover) Fd 4 ha (3 %) Seed supply Seedbed Light Soil moisture Browsing Insect damage (aphids) Vegetation. (See Hale 24 FCIN63)

3 Characterizing light levels in the understory Light measurement requires specialized equipment and appropriate measurement conditions Many studies indicate that stand characteristics such as basal area (Hale 23), SDI (Vales and Bunnell 1988), Relative Density (Comeau and Heineman 23) can be used to predict light levels We set out to determing if SDI might better than basal area as a predictor of light?

4 Density Size Relationships for SS and DF in GB and western Canada a) Sitka spruce (GB) b) Douglas-fir (GB) 1 1 Stand density (trees/ha) 1 Stand density (trees/ha) Quadratic mean diameter (Dq) (cm) Quadratic mean diameter (Dq) (cm) data Top 1% MAX Top 1% data Top 1% MAX Top 1% c) Sitka spruce (BC) d) Douglas-fir (BC) 1 1 Stand density (trees/ha) 1 Stand density (trees/ha) Quadratic mean diameter (Dq) (cm) Quadratic mean diameter (Dq) (cm) data Top 2% MAX data Top 1% MAX Top 1% Figure 2. Relationships between stand density and quadratic mean diameter for Sitka spruce and Douglas-fir based on OLS regression on the upper 1 percent of the data. Equations and parameter values for these lines are provided in table 1. Data from 499 SS (GB), 112 DF (GB), 2 SS (BC) and 389 DF (BC) plots

5 Revised SDI equations and SDI=N * (QMD/25) b Sitka spruce Britain b= 2.68* SDImax=1868 Canada b= SDImax=273 Douglas-fir Britain b= 1.864* SDImax=1491 Canada b= 1.241* SDImax=1815 Max SDI Stand density (trees/ha) Quadratic mean diameter (Dq) (cm) SS (GB) SS (BC) DF (GB) DF (BC) * b significantly different from 1.65 Comeau, P.G, White, M, Kerr, G, and Hale, S. E. [21] Maximum density-size relationships for Sitka spruce and coastal Douglas-fir in Britain and Canada. Forestry (in press).

6 Gap Fraction Diffuse Transmittance y =.7352x +.43 R 2 =.9725 y =.8578x R 2 = SS FD Linear (SS) Linear (FD) 5 hemiphotos from 32 thinned Sitka spruce plots (1 locations) and 21 thinned Douglas-fir plots (3 locations) Photos analyzed to determine GF using SLIM software (9º overhead view assumed) autothresholding used Tested several stand measures (basal area, tph, qmd, sdi,, height, crown depth) as predictors of GF using REML regression (SAS Proc GLIMMIX) Gap Fraction

7 SS GF results GF=exp( *baha-.641*tph) n=3 R2adj =.686 Ss Ss Gap Fraction Basal area (m2/ha) p25 p5 p75 AB CLOC COM GAR KLD TRALLWM GLAS Gap Fraction Stems/ha AB CLOC COM GAR KLD TRALLWM GLAS Expon. (p3) Expon. (p15) Expon. (p45) SS.6 Gap Fraction AB CLOC COM GAR TRALLWM GLAS GLED SDI GF=exp( *SDI-.68*tph) n=3 R2adj =.686

8 FD-GF results Fd FD Gap Fraction BETWS CLAR MOR pred Expon. (pred) Gap Fraction BETWS CLAR MOR 'pred' pred Basal Area (m2/ha) SDI GF=exp( *baha) R2adj=.85 GF=exp( *SDI) R2adj=.68

9 GF vs Basal Area.7.6 Gap fraction SS FD Basal area (m2/ha) SS GF=exp( *baha-.64*tph) FD GF=exp( *baha)

10 Sitka spruce GB 1 Stand density (trees/ha) Dq (cm) MAX RD=.6 (ZICM) RD=.15 (Crow n Closure) GF=.3 GF=.4 GF=.5 G=6 G=5 G=4 G=3 G=2 G=1 Figure 12. Stand density management diagram for Sitka spruce in Great Britain showing the positions of gap fraction (GF) lines for GF=.3,.4 and.5, the maximum size density line, the zone of imminent competition mortality (ZICM, at a relative density (RD) of.6) and the approximate position of the crown closure line (at a relative density of.15). Basal area isolines are shown (G=6, G=5, ; values in m 2 /ha). (D q =quadratic mean diameter for the stand).

11 Douglas-fir GB 1 Stand density (trees/ha) Dq (cm) MAX RD=.6 (ZICM) RD=.15 (Crow n Closure) G=6 G=5 G=4 G=3 G=2 G=1 GF=.3 GF=.4 GF=.5 Figure 13. Stand density management diagram for Douglas-fir in Great Britain showing the positions of gap fraction (GF) lines for GF=.3,.4 and.5, the maximum size density line, the zone of imminent competition mortality (ZICM, at a relative density (RD) of.6) and the approximate position of the crown closure line (at a relative density of.15). Basal area isolines are shown (G=6, G=5, ; values in m 2 /ha). (D q =quadratic mean diameter for the stand).

12 Are distance dependent measures better? (Douglas-fir 3 locations in Wales GFR y = e -.98x R 2 = Basal area (m2/ha) gfr cyb5 cyb4 atw1 GFR y = e x 1 R 2 = RD (based on SDInew equation) gfr cyb5 cyb4 atw1 GFR y = 4.722e -.819x R 2 = gfr cyb5 cyb4 atw1 GFR y = e -.74x R 2 = gfr cyb5 cyb4 atw1 C (Shotnoise) Hegyis Index Hegyis=sum(dbh/dist) Radius=15m

13 Light under an uneven-aged Douglas-fir stand SE BC study (Kyle Lochhead M.Sc.) indicates Height strata have different effects on light per unit basal area Simple indexes of limited use Table 3-1 Various stand density estimators used as predictors of light availability and separated by species. The following model was developed where DIFN 1.3 = a*exp(-b*fd - c*lw - d*pl) n =255. Stand Estimator a FD LW PL i 2 RMSE Basal Area/ha (.171) (.2417) (.229) (.5868) Trees/ha (.128) (.45) (.815) (.157) SDI/ha (.178) (.16) (.113) (.254) S Ht /1m (.149) -.49 (.42) -.35 (.5) (.849) Figure 3-1 Scatter plot showing the relationships between understory light and different stand parameters (total). Fitted line (blue) represents the effect when species composition is taken into account with nonsignificant variables held constant at their average. Red dotted lines signify 95% CI for population means. See table 2-2 for statistical description

14 Conclusions SDI should be calculated using regionalized formulas Maximum stocking of Sitka spruce and Douglas-fir lower in Britain than Canada For SS GF predicted as well by basal area and stems/ha as by SDI (SS), basal area better for DF For Sitka spruce - basal area below 3 required to create gf >.25 (diffuse light >25%) (but depends on density) Retained trees grow quickly (2 m 2 /ha/y) important to consider growth of overstory in planning levels of removal and cutting cycle. Douglas-fir - all measured stands had GFR>3 Overlaying GFR on the density QMD diagram could be useful as a planning tool These simple relationships work only in initial stages of transformation, not in irregular or uneven-aged aged stands

15 Acknowledgements Funding to support this research provided by the Scottish Forestry Trust Support from Forestry Commission, Forest Research Support from B.C. Ministry of Forests and Range for SE BC study BC Data from B.C. Ministry of Forests and Range, Inventory Branch and thanks to Alf Kivari and John Vivian

16 Thank-you Thank-you

17 Regeneration and light 1 1 Ss regen presence Ss regen presence GFR Total Transmittance (hemiphoto-slim) No Sitka spruce regeneration observed at GFR<.22 or T <17 (18 stands observed [Phil Comeau unpubl.]) Want gfr>.25