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Development of a productivity Index for Douglas-fir

Leith Knowles's study develops a productivity index for Douglas-fir using Site Index (SI) and Site Basal Area Potential (SBAP) metrics. The study proposes a combined index, the 500 Index, to predict the Mean Annual Increment (MAI) of Douglas-fir stands. Results show the sensitivity of the 500 Index to changes in silviculture practices, making it a valuable tool for forest management. The study concludes that the 500 Index, incorporating SI and SBAP, is crucial for understanding and predicting the productivity of Douglas-fir in various sites.

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Development of a productivity Index for Douglas-fir

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  1. Leith Knowles Development of a productivity Index for Douglas-fir

  2. Productivity Indices • Site Index (SI) • SI=MTH@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?

  3. Methods TSV=a*MTH*BA TSV=a*SIb*SBAPc MAI =TSV/rotation age

  4. SI and SBAP for 1365 sample plots

  5. SI and SBAP matrix

  6. 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

  7. Results 500 Index = a*SIb*SBAPc Where a=0.0971 b=1.344 c=0.0973

  8. 500 Index compared to MAI from DF NAT

  9. SBAP can be predicted from SI and 500 Index SBAP=(500 Index/a*SIb))d Where a=0.0971 b=1.344 d=1.028

  10. Sensitivity of 500 Index to changes in silviculture • Stocking @ age 10 years (1500 stems/ha) 200 stems/ha=1% change in 500 Index • MTH at thinning (15m) 1m=1.15% in 500 Index • Final crop stocking (500 stems/ha) 100 stems/ha=6.6% in 500 Index

  11. Latitude

  12. 500 index can be estimated by region

  13. ….. and by forest

  14. 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

  15. Questions and answers

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