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)]

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

Obs

erve

d -P

redi

cted

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=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

HMOD

DMOD

Percent of healthy growth

NR ΔDBH ΔHT

1.0 33% 60%

1.5 67% 82%

2.0 90% 94%

2.5 98% 98%

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 ORGANONValidate with remeasurement data

– 10-year remeasurement on all young plots at the end of 2007

Validate over multiple growth cycles

Questions?