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GUIDELINES for . . .
Spacer graphic Developing Stand Density Management Regimes

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Options analysis

    Production comparisons

      Tables A2-3 and A2-4 display some of the information generated by TIPSY for the coastal and interior scenarios, respectively. Yields are compared at a constant age which is close to the physical rotation ages given in the second section of the table. Economic analyses for coastal hemlock and interior pine are based on the log and lumber markets, respectively. To see a discussion of minor limitations regarding TIPSY's ability to differentiate between H- and I-grade logs, go to the online documentation, use the `Search for Help On...' option and type in `log grades.' The following summary applies to the pre-commercial thinning (PCT) of hemlock (Hw) or pine (Pl) or, if unspecified, both in these examples:

      • Merchantable volume is insensitive to thinning in this range.
      • Mean DBH increases with intensity of PCT.
      • Merchantable volume and DBH of prime trees increase but the latter is less sensitive to thinning than is the mean DBH of the stand.
      • Hw: The volume of I-grade logs increases but is offset by decreases in other grades. Harvest revenue improves somewhat.
      • Pl: Total lumber output (mostly 4_ and 6_ widths) and harvest revenue are higher but decline as residual density decreases. Spacing also elevates lumber recovery and harvest revenue.
      • Hw: Physical rotations increase; MAIs are stable; site values decline.
      • Pl: Physical rotations and MAIs are stable; site values decline.
      • Hw: Economic rotations are stable, but MAIs and site values decline.
      • Pl: Economic rotations and MAIs are stable; site values decline.
      • Ignoring the initial pre-treatment costs (discounting to age of PCT instead of 0) doubles the site value but does not alter the ranking of treatments.

    Table A2-3. Tactical options analysis for four western hemlock stand density regimes


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    Unthinned
    PCT to
    1200 sph
    PCT to
    900 sph
    PCT to
    600 sph

    Yield comparison [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age at comparison (yr) 100 100 100 100
    Merch. volume (m3/ha) 1 062 1 064 1 059 1 011
    All trees [0.0+]: Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - mean DBH (cm) 33.7 38.5 40.5 44.9
    - no. of trees 774 632 570 444
    250 prime trees: Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - merch. vol. (m3/ha) 758 804 823 874
    - mean DBH (cm) 47.2 50.3 51.3 53.7
    Logs (m3/ha): Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - Grade H 50 33 19 5
    - Grade I 262 366 413 499
    - Grade J 661 597 568 462
    - Grade U 65 53 46 35
    - Grade X 13 12 12 10
    - Grade Y 2 2 2 2
    - total 1 053 1 063 1 060 1 013
    Harvest revenue ($/ha) 96 582 99 841 100 293 98 526
    Physical rotation [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age of culmination of MAI (yr) 90 95 105 120
    MAI [= max] (m3/ha) 10.67 10.65 10.61 10.27
    Site value [< max] ($/ha) 1 056 746 583 307
    Economic rotation [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age of culmination of site value (yr) 80 80 80 85
    Site value [= max] ($/ha) 1 083 884 904 860
    MAI [< max] (m3/ha) 10.55 10.39 10.22 9.76
    Site value @ age 17 (PCT) ($/ha) 2 147 1 778 1 816 1 730

    Table A2-4. Tactical options analysis for four lodgepole pine density regimes


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    Unthinned
    PCT to
    1800 sph
    PCT to
    1400 sph
    PCT to
    1000 sph

    Yield comparison [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age at comparison (yr) 70 70 70 70
    Merch. volume (m3/ha) 349 366 357 335
    All trees [0.0+]: Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - mean DBH (cm) 20.0 23.5 24.8 27.6
    - no. of trees 1 404 1 093 962 741
    250 prime trees: Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - merch. vol. (m3/ha) 150 159 167 180
    - mean DBH (cm) 28.9 30.8 31.9 33.9
    Chips (BDU/ha) 61 63 61 57
    Lumber vol. (bd ft/ha): Spacer graphic Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    - 2 x 4 55 797 57 789 55 380 50 274
    - 2 x 6 17 000 20 041 20 164 20 007
    - 2 x 8 2 154 2 326 2 465 2 677
    - 2 x 10 2 645 3 659 4 933 7 378
    - total 77 596 83 814 82 942 80 336
    Lumber recovery (bd ft/m3) 222.1 228.9 232.5 239.5
    Harvest revenue 36 764 39 505 39 035 37 727
    Physical rotation [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age of culmination of MAI (yr) 70 70 70 75
    MAI [= max] (m3/ha) 4.99 5.23 5.10 4.81
    Site value [< max] ($/ha) 940 719 708 595
    Economic rotation [12.5+] Spacer graphic Spacer graphic Spacer graphic Spacer graphic
    Age of culmination of site value (yr) 60 60 60 60
    Site value [= max] ($/ha) 1 048 848 831 785
    MAI [< max] (m3/ha) 4.92 5.18 5.01 4.64
    Site value @ age 16 (PCT) ($/ha) 1 992 1 598 1 567 1 481

      In summary, the biological response of the stand to pre-commercial thinning slightly increased the harvest revenue. However, the economic analysis shows that the site value did not increase enough to cover treatment costs when all revenues and costs were discounted to a common point in time. This does not mean that spacing can not be undertaken to meet other management objectives (e.g., maintenance of wildlife habitat).

      Rotation ages in Tables A2-3 and A2-4 vary widely depending on the regime and criteria selected. However, the relationships of MAI to age and treatment (Figures A2-1 and A2-2) show that volume production is quite insensitive to both in this range with the exception of the heaviest treatment. TIPSY can draw these figures if each regime file is run in steps of five years from 0 to 160 (Hw) or 120 (Pl) years prior to plotting "MAI (merch) 12.5+" over "Age." Notice that thinning impairs volume production of coastal hemlock until the site is reoccupied, after which it catches up with the untreated stand. Recovery time is related to the intensity of thinning and site productivity. The situation with pine is more complex because utilization limits have a great impact on yield, particularly when the rotations are short.

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    Figure A2-1. Mean annual increment over stand age for four coastal western hemlock density regimes.

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    Figure A2-2. Mean annual increment over stand age for four interior lodgepole pine density regimes.

      Similar insight into the dynamics of stand development can be achieved by plotting other variables over age (e.g., volume, diameter, number of trees and prime tree statistics). It is also informative to display number of trees (stand table) and volume (stock table) by diameter classes. TIPSY-generated stand tables at age 100 (Hw) and 70 (Pl) show that the unthinned stand has many more trees in the smaller diameter classes. The difference increases with the intensity of treatment. However, thinning produces slightly more trees in the largest diameter classes.

      The corresponding stock tables for hemlock (Figure A2-3) and pine (Figure A2-4) are more meaningful than stand tables because they display volume, which is closely related to stand value. Notice that pre-commercial thinning shifts volume toward the larger diameter classes in both examples, which is the intent of this practice. A closer look at the untreated and thinned to 900 hemlock regimes (Figure A2-3) shows that 193 m3 of small wood (mostly in the 20 to 35 cm classes) is replaced with 181 m3 of large wood (mostly in the 50 to 65 cm classes). Spacing pine to 1400 trees/ha (Figure A2-4) converts 77 m3, in the 15 to 20 cm classes into 83 m3, most of which falls in the 30 to 35 cm classes.

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    Figure A2-3. Distribution of volume by diameter class at age 100 for the coastal western hemlock density regimes.

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    Figure A2-4. Distribution of volume by diameter class at age 70 for the interior lodgepole pine density regimes.

    Investment decision

      The site value of all density management regimes is positive over a wide range of ages for both hemlock (Figure A2-5) and lodgepole pine (Figure A2-6). This indicates that, in isolation, all regimes are economically efficient. However, all thinned stands have a lower site value than the comparable untreated regimes, indicating that the untreated regime is the most economically efficient choice in these examples.

      The economic outlook for spacing will only be favourable if the increase in tree diameters increases log size and value sufficiently to offset thinning costs compounded to harvest. Notice that DBH distributions shift by about 5 cm in Figures A2-3 and A2-4. TIPSY addresses the premium for piece size through the effect treatment has on log and lumber yields by dimension and the associated prices.

      The foregoing analysis indicates that alternative silviculture investment options, including treatments on other sites, should be investigated. Those options which yield higher net economic gains should be considered before investing in any of the thinning regimes in these examples.

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    Figure A2-5. Site value over stand age (economic efficiency) for four coastal western hemlock density regimes.

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    Figure A2-6. Site value over stand age (economic efficiency) for four interior lodgepole pine density regimes.

    Other considerations

      Figures A2-5 and A2-6 illustrate the effect of harvest timing on investment decisions. There is a 10 year plateau of economic advantage when the site value is at or near the optimum economic rotation age. Site value declines rapidly in later years due to the compounding effect of time on silviculture investments.

      If, for reasons of resource management constraints (e.g., VQO, ungulate winter range, community watershed requirements), the rotation must be extended or deferred beyond the period of maximum site value, it would be unwise, from a timber optimization perspective, to invest silviculture capital in pre-commercial thinning. Silviculture investments made under these circumstances will likely yield low or negative returns. Similar economic impacts result from spacing stands of low productivity with lengthy investment periods.

      Some assumptions used in the preceding analysis may not be based on the best available data for a specific site or area. Thinning costs, for example, were based on the "Linear Equation" option. Use of the "District Average" values raises the costs of thinning pine to 1400 trees by $154 and lowers the economic site value from $831 to $739. Managers should be aware of the relative sensitivity of the various assumptions in their analysis. Examples of sensitivity analysis follow.


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Copyright 1999 Province of British Columbia
Forest Practices Branch
BC Ministry of Forests
This page was last updated January 1999

Comments to: Tim Ebata <Tim.Ebata@gems8.gov.bc.ca>