Sean M. Garber April 26, 2007

1. Simulating growth impacts of Swiss needle cast in Douglas-fir:The blood, sweat and tears behind the ORGANON growth multiplier Sean M. Garber April 26, 2007

2. Introduction • Swiss needle cast (SNC): • Infects current year needles in Douglas-fir • Reduced gas exchange and photosynthesis • Cause premature loss of needles • Reduces tree and stand growth

3. Introduction • Necessary to have tools to predict growth losses • Only stand-level corrections are currently available • Rough approximations • Limited use for individual trees • Biological and economical assessments are difficult

4. Objectives • Develop modifier equations that will adjust diameter and height growth projections for SNC in ORGANON • Incorporate these equations into a DLL routine • Connect SNC module to Windows version of ORGANON

5. Data From Swiss Needle Cast Cooperative study plots Younger stands Older stands

6. Data • Plot measurements • Plot for all trees ≥ 5 cm DBH tagged • Smaller subplot for all trees > 1.37 m HT and < 5 cm • Measured all DBH’s • Subsampled HT and HCB

7. Data • Needle retention (NR) • Number of needle age classes • Measure of SNC infection levels • Average of 10 trees per plot • Range was from 1 to 4.5 years

8. Analysis • Untreated plots grown in ORGANON-SMC • Used a single 4-year growth period from each plot • First 4-year growth period from each plot • Multiplied by 1.25 to match ORGANON’s 5-year time step

9. Analysis • All trees included in ORGANON runs • Including small trees and hardwoods • Site index • Fractional ages in young stands • Bruce’s (1981) site index based on earliest measurements • Less affected by SNC • Highly variable in younger stands • Range 80-170 ft

10. Modifier analysis • Calculation of modifiers • ORGANON-SMC predictions assumed to be healthy stand • DMOD = predicted ΔDBH / (observed ΔDBH ×1.25) • HMOD = predicted ΔHT / (observed ΔHT ×1.25) • Fitting modifiers • Only used trees with DBH, HT, CR

11. Modifier analysis • Response variables were the modifiers • Model as a function of needle retention • Growth impact expected to follow a Weibull model form: MOD = [1 – exp(-b1NRb2)]

12. Model fitting Infected tree: MOD<1.0 Healthy tree: MOD=1.0

13. Model fitting • Problems • Asymptote was > 1.0 • Residual bias with tree position

14. Raw residuals from DMOD fit on BAL Bias at lower crown positions Observed -Predicted

15. Crown Position Bias • Bias only seen in DMOD residuals • Most likely an artifact of younger naturally established trees • Other small trees in small gaps • No evidence that this was related to SNC!

16. Final model forms Diameter growth modifier: DMOD=β0[exp(β1BAL1.4)] ×[1 – exp(-β2NRβ3)]+ε Accounts for BAL bias Asymptote Height growth modifier: HMOD=γ0[1 - exp(-γ1NRγ2)]+ε

17. Results • High variability in modifier values • DMOD and HMOD trend w/NR were significant • Asymptotes significantly greater than 1.0 • Healthy trees grew faster than ORGANON-SMC predicted • DMOD = 1.2816 (0.0362) • HMOD = 1.1925 (0.0171) • ΔDBH more sensitive to SNC than ΔHT

18. HMOD DMOD

19. Percent of healthy growth

20. Application of Modifiers Adjusted ΔDBH = predicted ΔDBH × DMOD Adjusted ΔHT = predicted ΔHT × HMOD

21. Module • Applies to unthinned and unfertilized stands • Applied to SMC and NWO variants • Needle retention can be changed by user during runs • Dynamic link library has been written • Currently being incorporated into Windows version of ORGANON

22. What’s next? • Incorporate into ORGANON • Validate with remeasurement data • 10-year remeasurement on all young plots at the end of 2007 • Validate over multiple growth cycles

23. Questions?