Development of a productivity Index for Douglas-fir

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Development of a productivity Index for
Douglas-fir

• Leith Knowles

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Productivity Indices

• Site Index (SI)
• SIMTH_at_40years. Independent of silviculture
• Site basal Area Potential (SBAP)
• Derived from sample plots. The SBAP is the value
  that makes the growth model BA increment best
  match the sample plot BA increment. The overall
  plot mean SBAP is calculated as the
  period-weighted mean over all increment periods.
  Independent of silviculture
• Is it possible to develop one simple volume index
  by combining the two?

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Methods
TSVaMTHBA TSVaSIbSBAPc MAI TSV/rotation
age
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SI and SBAP for 1365 sample plots
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SI and SBAP matrix
min max interval Number
SI 20m 40m 4m 6
SBAP 1.0 2.4 0.2 8
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What is 500 Index?

• 500 index is simply the predicted MAI of a stand
  planted at 1500 stems/ha, thinned to 500 stems/ha
  by 15m MTH, and grown to age 40 years

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Results

• 500 Index aSIbSBAPc
• Where
• a0.0971
• b1.344
• c0.0973

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500 Index compared to MAI from DF NAT
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SBAP can be predicted from SI and 500 Index

• SBAP(500 Index/aSIb))d
• Where
• a0.0971
• b1.344
• d1.028

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Sensitivity of 500 Index to changes in
silviculture

• Stocking _at_ age 10 years (1500 stems/ha)
• 200 stems/ha1 change in 500 Index
• MTH at thinning (15m)
• 1m1.15 in 500 Index
• Final crop stocking (500 stems/ha)
• 100 stems/ha6.6 in 500 Index

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Latitude
Latitude a b c
380S 1.000 1.344 0.973
420S 0.097 1.344 0.973
460S 0.094 1.344 0.973
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500 index can be estimated by region
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.. and by forest
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Conclusions

• Both SI and SBAP are needed to explain site
  productivity
• These can be combined to predict MAI for a
  standard regime (500 Index)
• Productivity of Douglas-fir on most sites in NZ
  is now expressed in terms of 500 Index
• 500 Index included in DF Calc V2

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Questions and answers