Forecaster calculator works by utilising geographic location. When you select a point on the map, Forecaster Calculator will cross reference it with a number of geographic “surfaces” which predict some growth-related parameters based on the location. These include:

• Altitude (metres above sea level).
• Site index. For radiata this is the average height of the 100 largest diameter stems per hectare at age 20 years. (Goulding 2005).
• 300 Index. This is the stem volume mean annual increment (MAI) at age 30 years of a stand grown to a reference regime with final stocking of 300 stems/ha. (Kimberley et al. 2005).
• Mean Annual Air Temperature. From Land Environments of New Zealand (LENZ) data.

Some of these “surfaces” have been developed by dividing the country up into a fixed sized grid and assigning values to each cell. Forecaster Calculator then averages non-missing surface values within a 15ha radius of the selected location. Site indices are applicable to tree stock with a genetic growth and form (GF) rating of 14.

Note that there is currently no surface for the 500 Index (which is required when simulating Douglas-fir) so a value must be entered. The article Douglas-fir - The Current New Zealand Scene, NZJF (Ledgard et. al. May 2005) has a table with some good starting values: South Waikato - 22.4, Rotorua-Taupo/East Coast - 18.3, Hawkes Bay - 14.6, Central North Island (Karioi) - 24.9, Lower North Island - 14.1 Nelson/Marlborough - 18.9, Westland - 16.6, Canterbury - 19.5, Otago - 19.7, Southland - 21.8. An overall average for New Zealand is given as 18.4.

The silvicultural regime is specified by a list of commands, each of which comprises a condition, such as the age of the stand, and a series of one or more events such as plant, prune, thin or clear-fell. As the calculator requires only the basic parameters for these events the following defaults are assumed:

Planting – stock is GF 14.
Pruning – pruning is to a prune height with the larger, taller stems selected in preference, the ordering strictness set at 3 to allow for some spacing considerations in the stem selection. The number of stems to prune is specified.
Thinning – only waste thinning is supported. The residual stocking is specified and stems are selected from the smallest DBH and Height with an ordering strictness of 3.

To run a regime in Forecaster Calculator, a measurement of the crop is required as the start-point for the growth projections. If a measurement event is not supplied then one is generated using the 300 Index growth model by using the supplied site index and 300 index. The date of this generated measurement event is calculated from the plant year and crop age at the first silvicultural event.

Eight log product definitions are used in Forecaster Calculator’s cutting strategy when simulating Domestic Radiata. These align with the set in the Radiata Pine Calculator spreadsheet. Six log product definitions are used with the Export Radiata cutting strategy. Four are used when simulating Douglas-fir.

The Cutting strategies for both the Radiata Pine and Douglas-fir have a cutting cost of $1.00. This ensures a long log is preferred to two shorts of equal total value. The bucking mode is set to maximum value, that is, each stem piece is cut to produce the mix of logs that will yield the maximum value. This is a reproducible strategy that aligns with the predictions made by most pre-harvest inventory systems such as YTGen.

Structural (Framing) Regime

On an average site (site index 30, 300 index 26), this regime was constructed as follows:

Plant 1000 s/ha;
Thin at age 5.5 to 800 s/ha;
Thin at age 10 to 500 s/ha;
Clearfell at age 30.

The results in terms of the mix of log product volumes are shown below. Differences in the percent of TRV by log grade are listed.

TSV = total standing volume inside-bark at age 30 (m3/ha).
TRV = total recovered volume at age 30 (m3/ha).

The TSV values are very close as expected. The percentage recovered yield predicted by Forecaster Calculator was 85%, which is the average value suggested in the spreadsheet. The grade mix is similar apart from S2 and Pulp where Forecaster Calculator predicted more S2 volume and less pulp.

Clear-wood (Pruned) Regime

On the same site a pruned regime was constructed as follows:

Plant 1000 s/ha;
Prune 450 to 2.4m at age 5;
Thin at age 5.5 to 700 s/ha;
Prune 400 to 4.6m at age 7;
Prune 350 to 6m at age 10;
Thin at age 10 to 350 s/ha;
Clearfell at age 30.

Results are shown below.

TSV = total standing volume inside-bark at age 30 (m3/ha).
TRV = total recovered volume at age 30 (m3/ha).

Forecaster Calculator predicted 84% recovery for this regime and, again, estimated more S2 volume than the spreadsheet.

Discussion

No attempt was made to tune the log mix proportions to any pre-conceived set. However such adjustment would be possible in Forecaster desktop by varying the parameters of the “quality” models, that is, branching, sweep and forking. For example, a higher probability of large branches will tend to reduce the proportion of S grades. Adjustments can also be made by varying the relative price /m3 of the log grades.