9.6 Silviculture System
This section is used to specify which silviculture system will be used to harvest each polygon in the first and subsequent rotations.
A selection can be made to account for either a clearcut or some form of alternate silviculture system (partial cut) on the selected polygon. Clearcuts with reserves should be considered clearcuts for this model, and entered as only the net area harvested. Patch clearcuts could be split polygons. The model will default to clearcut unless otherwise selected.
The first harvest entry will occur at or later than the harvest age selected in Polygon Data (under Yield Type, Harvest white box, refer to section "9.7.2 Harvest Age" page 9-51). The actual harvest age will depend on the order selected in the Calculations screen and actual cue in the line of polygons being harvested.
9.6.1 Clearcut
To activate clearcut, click on the Clearcut radio button. Use this system for any polygon that will approximate a clearcut, including clearcut with reserves and commercially thinned polygons (note a commercial thinning feature may be available in subsequent releases of WOODLOT.)
The first harvest entry will occur at or later than the harvest age selected in Polygon Data (under Yield Type, Harvest white box, refer to section "9.7.2 Harvest Age" page 9-51). The actual harvest age will depend on the order selected in the Calculations screen and actual cue in the line of polygons being harvested.
9.6.2 Partial Cut
Acceptable Values: 1-50%, 10-999 Years
[Default] values are updated directly from harvest parameters.
To activate the partial cut feature, click on the Partial Cut radio button. Enter the two-digit percentage volume to be removed on the first entry, and the minimum re-entry period in years.
WOODLOT uses a simple approximation technique to predict future yields and measure in-growth from partially cut stands, using VDYP natural yields and a Partial Cut Adjustment Factor (PCAF). This method is used in the absence of yield models for partially cut stands in BC, and has been accepted by MOF staff for use in WOODLOT. (The use of recently developed partial-cut yield models such as PrognosisBC is being considered for use in a subsequent release of WOODLOT.)
In WOODLOT, partial cutting works in the following manner:
- The Partial Cut feature is selected with % removal and re-entry periods specified.
- Yield curves are derived, as they would be for all polygons from the Calculate Yields command. Partial cutting uses only VDYP natural yields in WOODLOT.
- The first harvest entry will occur at or later than the harvest age selected in Polygon Data (under Yield Type, Harvest white box, refer to section "9.7.2 Harvest Age" page 9-51). The actual harvest age will depend on the order selected in the Calculations screen and actual cue in the line of polygons being harvested.
- To measure volume removed on the first entry, WOODLOT will first determine the residual volume to be reduced to based on the % removal. The volume to be reduced to is the difference in volume at the specified harvest age, less the % removal.
- To model the in-growth and volume to be removed on subsequent entries, the residual volume is compared to the VDYP yield curve, and assumed to grow like a similar stand at the younger age that matches this residual volume. The stand is assumed to grow at the same rate and stocking as the naturally occurring well-stocked stand did, and is re-harvested at the specified re-entry period.
- To adjust for any upward or downward bias of this methodology, a Partial Cut Netdown Factor (PCAF) has been introduced in the Harvest Parameters screen. The yield generated is reduced (or can be increased) by this amount. WOODLOT defaults the PCAF to 0.8, which assumes a conservative 20% netdown. This can be reset in the Harvest Parameters screen. The Partial Cut Adjustment Factor (PCAF) is applied to the in-growth, and the net amount is used for harvest calculations
(i.e. volume used for Partial cut polygon in harvest calculations = in-growth * PCAF)
Refer to section "11.4
Harvest Parameters" page 11-66 for more information on setting a Partial Cut Adjustment Factor, which is applied to all partial cut stands on the woodlot.
- At reentry age, the in-growth is removed, and the stand is reduced to the younger age again. The stand re grows again, until it is harvested at the next reentry period, and the cycle continues.
A graphical and tabular example is provided below.
| Example Item | Numerical values | Comment |
|---|
| Current Age of stand (years) | 25 | Does not affect calculations. If the current age is > the harvest age, then the current age and volume at this age will be used for the first harvest age. |
| Target Harvest Age (years) (existing Management = 1st harvest age) | 100 | User selected |
| Total Volume at target harvest age (m3/ha) | 400 | VDYP generated |
| % volume to be removed | 15% | User selected |
| Minimum Reentry period (years) | 30 | User selected |
| Volume to be harvested down to in all partial cuts (m3/ha) | 400-(15%*400) = 340 | WOODLOT calculated as the lower bench mark value to measure from. |
| Example actual harvest age (years) | 120 | Typical example actual harvest age used by WOOLDOT due to delayed sequence in Calculations or cue |
| Total Volume at actual harvest age (m3/ha) | 420 | VDYP generated |
| Volume removed at first harvest (m3/ha) | 420-340 =80 | Volume that WOODLOT will include in the harvest rate calculations |
| Assumed stand age which in-growth is assumed to occur from (years) | Volume of 340 m3/ha occurs at 85 years age on a normal VDYP stand | VDYP generated |
| Assumed stand age at next and subsequent harvests (years) | 85+30 years=115 | years WOODLOT will use the volume at this age |
| Volume for a normal stand at 115 years (m3/ha) | 410 | |
| In-Growth (m3/ha) | 410-340=70 m3/ha | Unadjusted in-growth, which will vary depending on the actual subsequent harvest age |
| PCAF | 0.8 | User selected. This assumes a 20% reduction due to delayed growth and not fully stocked stand |
| In-growth volume used for subsequent harvest calculation | 0.8*70=56 | Volume that WOODLOT will include in the subsequent harvest rate calculation. |
Note: until recently, the TSR method assumes a process whereby the volume available on reentry equals a constant mai x years growth, based on some reduced mai.
Note: Selecting partial cut will turn off any TIPSY yield tables. Only VDYP can be used in conjunction with Partial Cut at this time. Future releases of WOODLOT may use partial cut yield curve information in exchange for this option.
9.6.3 Commercial Thin
This feature is not enabled for version 2.1 of WOODLOT. Below is an example of how the calculation may work.
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