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Yield Implications of Variable Retention Harvesting

Western Mensurationist Meeting Victoria, July 3, 2003. Yield Implications of Variable Retention Harvesting. VR Team: Mario Di Lucca, Ken Polsson, Jim Goudie, and Tim Bogle. Research & Timber Supply Branches B. C. Ministry of Forests, Victoria. In the Fraser TSA.

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Yield Implications of Variable Retention Harvesting

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  1. Western Mensurationist Meeting Victoria, July 3, 2003 Yield Implications of Variable Retention Harvesting VR Team: Mario Di Lucca, Ken Polsson, Jim Goudie, and Tim Bogle Research & Timber Supply Branches B. C. Ministry of Forests, Victoria

  2. In the Fraser TSA From a Timber Supply Perspective

  3. Variable Retention (VR)Impacts on Sustainable Harvest Levels • Will VR reduce harvest levels? • If so, by how much? • What are the ecological merits of • aggregated vs. dispersed retention? • What are the G&Y impacts? • What are the economic implications?

  4. Variable Retention (VR) • Background • J. Franklin (UW) “New Forestry” • Clayoquot Scientific Panel (1995) • Weyerhaeuser (1998) & • TASS simulations - Goudie (1998) • Timber supply analysts request VR volume estimates for the Fraser TSA • Research Branch develops tools to predict VR yields of: • regenerated stands • excluding retained trees

  5. TASS Simulations (Goudie, 1998) Weyerhaeuser Retained stand age 100 years - Regenerated stand age 10

  6. Methods to Estimate Variable Retention Yield Curves using TASS 1. Simulate Actual Site VR Yield Curves Cutblock Variables TASS TSR

  7. Methods to Estimate Variable Retention Yield Curves using TASS 1. Simulate Actual Site VR Yield Curves Cutblock Variables TASS TSR 2. Derive Relationships TASS VRAF Function VR Yield Curves Simulation Variables TIPSY TSR Cutblock Variables

  8. Method 1. Simulate Actual Site in the Fraser TSA 60 years old cutblock after VR harvest TASS layout

  9. Cutblock Statistics(ArcInfo) Cutblock area: 31.02 ha Retention area: 4.38 ha (15 groups ranging from 0.05 to 2.1 ha) Percent retention: 14% Perimeter or edge retained: 111 m/ha

  10. TASS Simulations • Simulate VR cutblock scenario: • Plant: 4444 trees/ha Fd on site 35 (age 0) • Grow to: age 60 • Harvest to mimic cutblock layout • Plant: 1400 Cw trees/ha • Grow to: age 160 & harvest Simulate comparable clearcut scenario & calculate: VRAF = VR vol/Clearcut vol = 0.82 (age 100)

  11. Clearcut vs. Regenerated (VR) Yields Average Reduction 1.00 0.83 Clearcut VR Previous Stand

  12. Method 2. Derive Relationships • Matrix of TASS simulations • Select important variables & • Derive VRAF equations: • VRAF(sp) = f (edge, % retention, SI, • overstory age or height, etc.)

  13. Method 2. Derive Relationships • Matrix of TASS simulations (1107 runs): • Site Index: 25, 30 & 35 • Harvest ages: 70, 130 & 200 years • Retention level: 10, 20 & 30% • 15 rectangular group sizes: 0.01 to 4 ha • Number of groups: 1 to 9 • 27 dispersed tree regimes: 20 to 240 trees/ha • Constants: • Original stand: 5000 trees/ha FDc natural • Regenerated stand: 1200 trees/ha planted & • 600 trees/ha natural • Retained groups: rectangularity of 1:6.25

  14. Partial matrix of TASS simulationsSI 30, Overstory age 70 & 10% Retention Run 1: 1 group - 1.5 ha Run 2: 152 groups - 0.01 ha (1 ha) Run 3: 718 groups (trees) - 0.0015 ha (1 ha) (15 ha)

  15. Partial matrix of TASS simulations Clearcut 1 group 152 groups 718 groups

  16. Partial matrix of TASS simulations Avg. Yield Reduction 1.00 Clearcut 0.91 1 group 0.72 0.73 152 groups 718 groups VRAF = VR volume/Clearcut volume

  17. Method 2. Derive Relationships • Matrix of TASS simulations • Select important variables & • Derive VRAF equations: • VRAF(sp) = f (edge, % retention, SI, • overstory age or height, etc.)

  18. Select important variables to estimate VRAF using TASS • Species & Site Index • Overstory retained stand: • Edge length > f (group shape, size & number) • % retention • Top height /age • Regenerated stand: • Top height

  19. Edge Effect Retained stand age 100 years - Regenerated stand age 10 0 m edge 118 m edge 235 m edge 200 m edge 352 m edge 910 m edge No trees will grow under the overstory canopy (black areas) TASS Simulations (Goudie, 1998) of Weyerhaeuser treatments

  20. VRAF as affected by edge length, no. & group size Run 1: (1 Group) Run 2: (152 Groups) Run 3: (718 Groups) VRAF declines (< 1.00) as: • Edge length increases by: • increasing number of groups • decreasing group size

  21. VRAF as affected by % Retention & Overstory Age VRAF declines (< 1.00) as: • % retention increases • overstory age decreases

  22. VRAF as affected by Site Index & Overstory Topht SI 35 SI 25 SI 30 VRAF declines (< 1.00) as: • SI increases • overstory top height decreases

  23. Method 2. Derive Relationships • Matrix of TASS simulations • Select important variables & • Derive VRAF equations: • VRAF(sp) = f (edge, % retention, SI, • overstory age or height, etc.)

  24. 10% 20% 30%

  25. VRAF Segmented Regression Function VRAF = 1- (b * Edge + c * (Edge - x0) * d1 + f * (Edge - x1) * d2) 1st Slope: b = b0 + b1* SI + b2 * retht + b3 * perc + b4 * topht Slope change: c = c0 + c1* SI + c2 * retht + c3 * perc + c4 * topht 2nd slope change: f = f0 + f1 * SI + f2* retht + f3 * perc Where: Edge = Edge length (m/ha) SI = Site index Retht = Overstory top height Perc = % retention Topht = Regenerated top height

  26. Fitted VRAF Function R2 = 0.993

  27. Retention 10% 20% 30%

  28. Percent retention: 14% Edge length: 111 m/ha Overstory height: 30 m Overstory age: 60 yrs. TIPSY ver. 3.2 VRAF = 0.83 Fraser TSA Cutblock

  29. Variable retention vs. clearcut yields & value at age 60 VRAF = 0.83

  30. CC 200 Overstory Age 130 70 CC % = b * ba ** c Where: b = b0 + b1 * retht c = c0 + c1 * SI

  31. Variable Retention Harvesting Effects on Timber Supply

  32. % retention edge length SI top height of regenerated trees top height/age of overstory trees Variable Retention Summary VRAF declines (< 1.00) and the relative yield of regenerated stands decreases as:

  33. Variable Retention Summary The primary factor affecting VRAF is: the amount and distribution of the retained trees which will compete for the regenerated growing space

  34. Current & Future Development • incorporate VRAF into TIPSY • address other species • model impact of windthrow & pests • incorporate VRAF into TASS III which is linked to a light model

  35. TASS with and without light model TASS II TASS III

  36. TASS with and without light model TASS II TASS III

  37. TASS with and without light model TASS II TASS III

  38. TASS with and without light model TASS II TASS III

  39. TASS II TASS III

  40. TASS II TASS III

  41. Questions?

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