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Application of the New Zealand Douglas-fir stand-level growth model to data from the PNW

This study applies the New Zealand Douglas-fir stand-level growth model (DF NAT) to data from the Pacific Northwest (PNW). The study examines the relationship between stand-level variables such as site index (SI), basal area (BA), and mortality. The results show that despite some differences, the DF NAT model works well in the PNW region.

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Application of the New Zealand Douglas-fir stand-level growth model to data from the PNW

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  1. Leith Knowles and Lars Hansen Application of the New Zealand Douglas-fir stand-level growth model to data from the PNW

  2. NZ stand-level growth model (DF NAT) • Based on data from 1600 permanent plots • MTH = fn(SI, age and latitude) • Current annual BA increment = fn(SBAP, age, crown, competition) • Mortality = fn(stocking, DBH) based on Reineke’s 3/2 rule • BA after thinning: BA2 = BA1*(N2/N1)a

  3. PNW validation data • Jim Flewelling facilitated access to data from the Stand Management Cooperative, University of Washington • 27 silvicultural trials (installations) • 303 sample plots • Stands 3-28 yrs of age • Roger Fight, US Forest Service, PNW Research Station also contributed to the study

  4. Fit of PNW data against NZ ht/age curves

  5. Ht/age curves refitted to PNW data

  6. New PNW ht/age curves

  7. Cumulative distribution of Site Index PNW NZ

  8. In PNW, SI increases with stocking

  9. NZ mortality function slightly underpredicts for PNW

  10. Different definitions for height to crown base • PNW: height above ground to lowest whorl where 3 out of 4 quadrants contain live branches • NZ: the average of height above ground to lowest live branch, and height above ground to lowest whorl with majority of branches live

  11. Predicted vs observed crown length for PNW data

  12. Thinning coefficient fitted for each thinning on each plot BA after thinning: BA2 = BA1*(N2/N1)a • PNW first thinning a = 0.77 • PNW second thinning a = 0.82 • Average NZ a = 0.71 • Average GB a = 0.66 • Average Germany a = 0.83

  13. SBAP sets BA ‘level’

  14. Cumulative distribution of SBAP PNW NZ

  15. SBAP in PNW trials independent of stocking

  16. Site Index and BA potential are poorly correlated

  17. 500-Index Volume MAI (m3/ha/yr) for a stand that has been thinned to waste to 500 stems/ha by 15m MTH, and grown on to age 40 years • Best growth installation 717: 17.4 m3/ha/yr • Poorest growth installation 501: 5.5 m3/ha/yr • Average for 27 installations: 12.4 m3/ha/yr • Compares to NZ average of 18.4 m3/ha/yr

  18. 500 index for 27 PNW installations

  19. Overall, DF NAT works well against PNW data

  20. Conclusions • SI similar (32m @ 40 years) • SBAP higher in NZ (1.88) vs PNW (1.2) • 500-index higher in NZ (18.4) vs PNW (12.4) • Slightly higher mortality in PNW • DF NAT needed new height-to-crown-base prediction function • Despite productivity differences (BA not SI), DF NAT works well in PNW • Valuable to repeat the exercise in 5-10 years

  21. Questions and answers

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