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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
availableRough approximationsLimited use for individual treesBiological 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
Study BH Age range (yrs)
Plots Number of
periods
Growth interval
(yrs)
GIS 5-30 76 3 2
PCT 7-18 23 3 2
CT 19-61 30 1 or 2 2
RCT 33-63 22 1 4
Youngerstands
Olderstands
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
measurementsLess affected by SNCHighly variable in younger standsRange 80-170 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(-b1NRb2)]
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=β0[exp(β1BAL1.4)] ×[1 – exp(-β2NRβ3)]+ε
Height growth modifier: HMOD=γ0[1 - exp(-γ1NRγ2)]+ε
Asymptote Accounts forBAL 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 = 1.2816 (0.0362)– HMOD = 1.1925 (0.0171)
ΔDBH more sensitive to SNC than ΔHT
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 ORGANONValidate with remeasurement data
– 10-year remeasurement on all young plots at the end of 2007
Validate over multiple growth cycles