Long term effects of alternative group selection harvesting designs on stand production. C. Halpin, C.G. Lorimer, J.J. Hanson, B.

Transcription

1 Long term effects of alternative group selection harvesting designs on stand production C. Halpin, C.G. Lorimer, J.J. Hanson, B. Palik

2 Objectives To assess group selection s impact on Stand-level volume production Stand-level growing space efficiency Tree-level volume production Tree-level growing space efficiency 2

3 Approach 3

4 Large trees (>17m tall) grow in diameter Small trees (<17m tall) grow in height Diameter growth (mm/yr) Tree diameter at breast height (cm) 4

5 Exposed and facing gap Exposed and not facing gap Shaded (15% stocking) Crown growth (cm) Tree diameter (cm) 5

6 8 Observed mortality Predicted mortality 6 Dead Trees Risk Category 6

7 Species of new saplings is influenced by overstory composition 7

8 Validation Comparing CANOPY simulations of standard single-tree selection against NH-25 field data for the same treatment: CANOPY Prediction NH-25 Measurement %Diff Survivor Growth (m 2 /ha/yr) % Mortality (m 2 /ha/yr) % Harvest Rate (m 3 /ha/yr) % 8

9 (a) (b) Treatments a) Standard STS b) GS+STS 8m 2, 3% c) Clearcutting w/ Thinning d) GS 8m 2, 12yr (c) (d) 9

10 Methods Simulated 1 reps of each treatment Used last 15 years of simulation to compute annualized volumetric yield and mortality Life-cycle inventory for individual trees A cohort of trees is tracked from birth to death 5-year volume increments are used to compute yield and efficiency averaged by size class 1

11 Hypotheses H1: Group size and the percentage of the stand occupied by groups will not affect net production rate H2: Under group selection alone, net production will decline as rotation age increases H3: Increases in sapling/pole GSE will not increase stand-level production markedly because the sapling/pole component produces only a small fraction of the total 11

12 Stand-level Production Net Production Mortality Industrial STS Heavy STS Standard STS GS+STS 8m2, 3% Clearcutting w/ Thinning GS 8m2, 12yr Clearcutting

13 Group Selection with Single-tree Cutting between groups Net Production (m 3 /ha/yr) % 3% 5% 9% Opening Size (m 2 ) 13

14 Group Selection Alone Net Production (m 3 /ha/yr) yr 12yr 135yr Opening Size (m 2 ) 14

15 Relative volume produced by trees in each size class Large Mature Pole Sapling Standard STS GS+STS 8m2, 3% Heavy STS Clearcutting w/ Thinning GS 8m2, 12yr Clearcutting Industrial STS % Total Production 15

16 Lifetime Average GSE ECA Large Mature Pole Sapling Standard STS GS+STS 8m2, 3% Heavy STS Industrial STS GS 8m2, 12yr Clearcutting w/ Thinning Clearcutting GSE ECA (dm 3 /m 2 /yr) 16

17 Production and Stand-level GSE TCA TCA Efficiency Net Production Net Production (m^3/ha/yr) 17

18 Relative Production of Clearcutting and Standard STS 9 Standard STS Clearcutting w/ Thinning Cumulative Cut (m^3/ha) Simulation Year 18

19 Evaluation of Hypotheses H1: Group sized/extent does not affect net production Supported by data H2: Under group selection alone, net production will decline as rotation age increases Supported by data H3: Increases in sapling/pole GSE will not increase stand-level production markedly because the sapling/ pole component produces only a small fraction of the total NOT supported by data 19

20 Concluding Remarks Paradox of efficiency vs yield Clearcutting without thinning is less productive than STS because of unsalvaged mortality Clearcutting with thinning is very similar in production to STS despite clear GSE advantages GSE advantage is mitigated by lower site occupancy 2

21 Questions? 21

22 Potential Production of Clearcutting and Standard STS 9 Standard STS Clearcutting w/ Thinning Potential Cut (m^3/ha) Simulation Year 22

23 GSE ECA within a size class Large Mature Pole Sapling GS 8m2, 12yr Heavy STS Industrial STS GS+STS 8m2, 3% Standard STS Clearcutting w/ Thinning Clearcutting

24 Relative volume harvested from each size class Large Mature Pole Sapling Standard STS GS+STS 8m2, 3% Clearcutting w/ Thinning Heavy STS Industrial STS GS 8m2, 12yr Clearcutting % Total Production 24

25 Observed Predicted 25

26 2 5 Trees / ha Tree diameter (cm)

27 Over 13, trees 27