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

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

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

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

Data StudyBH Age range (yrs) PlotsNumber of periods Growth interval (yrs) GIS PCT CT or 22 RCT Younger stands Older stands From Swiss Needle Cast Cooperative study plots

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

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

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

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 ft

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

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(-b 1 NR b 2 )]

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

Model fitting Problems – Asymptote was > 1.0 – Residual bias with tree position

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

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!

Final model forms Diameter growth modifier: DMOD=β 0 [exp(β 1 BAL 1.4 )] ×[1 – exp(-β 2 NR β 3 )]+ε Height growth modifier: HMOD= γ 0 [1 - exp(- γ 1 NR γ 2 )]+ ε Asymptote Accounts for BAL bias

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 = (0.0362) – HMOD = (0.0171) ΔDBH more sensitive to SNC than ΔHT

HMOD DMOD

Percent of healthy growth NR Δ DBH ΔHT 1.033%60% 1.567%82% 2.090%94% 2.598%

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

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

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

Questions?

Conclusions Healthy plots grow 20-30% faster in than ORGANON predicts – Short time period (influence of good years?) Confounding effects of SNC and estimation of site index in young stands Appears pattern with basal area in larger trees mostly an artifact of stand structure Appears work adequately