1 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 Western Mensurationist Meeting Victoria, July 3, 2003

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

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

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

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

9 Cutblock Statistics (ArcInfo) Cutblock area: 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 Previous Stand Average Reduction Clearcut VR Clearcut vs. Regenerated (VR) Yields

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

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 Run 1: 1 group ha (15 ha) Run 2: 152 groups ha (1 ha) Run 3: 718 groups (trees) ha (1 ha) Partial matrix of TASS simulations S I 30, Overstory age 70 & 10% Retention

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

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

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

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 edge118 m edge235 m edge 200 m edge910 m edge352 m edge No trees will grow under the overstory canopy (black areas) TASS Simulations (Goudie, 1998) of Weyerhaeuser treatments

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

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 25 SI 35 SI 30 VRAF declines (< 1.00) as: SI increases overstory top height decreases

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

24 10% 20% 30%

25 VRAF Segmented Regression Function VRAF = 1- ( b * Edge + c * (Edge - x0) * d1 + f * (Edge - x1) * d2) 1st Slope: b = b 0 + b 1 * SI + b 2 * retht + b 3 * perc + b 4 * topht Slope change: c = c 0 + c 1 * SI + c 2 * retht + c 3 * perc + c 4 * 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 R 2 = 0.993

27 10% 20% 30% Retention

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 Overstory Age CC % = b * ba ** c Where: b = b 0 + b 1 * retht c = c 0 + c 1 * SI

31 Variable Retention Harvesting Effects on Timber Supply

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

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 III TASS II

40 TASS II TASS III

41 Questions?