Jette Reeg*, Thorsten Schad°, Jane Tang°, Tilghman 

Hall°, Thomas Preuss°, Andreas Solga°, Florian Jeltsch*

Modeling Population and Community 

Effects of Herbicide Drift - Xplicit-IBC

*University Potsdam, °Bayer CropScience 

EMPM Oct. 2014
Problem Formulation

Risk assessment for Non-Target Terrestrial Plants (NTTP) 

(endangered or non-endangered) needs to account for :

• Agricultural activities (eg, cropping, chemical use pattern)

• Prevailing environmental conditions and climate conditions

• Inter- and intra-specific competition with a local plant community

Page 2

An integrated modeling approach was developed for 

NTTP risk assessment using 

• a local-scale plant Individual Based Community 

model (IBC) capable of simulating the dynamics and 

local effects of herbicides to NTTP species, and 

• a probabilistic model for estimating spatially and 

temporally explicit exposure and effect based 

landscape data (Xplicit)

uni-giessen.de
Xplicit -IBC Overview

- From Herbicide Use to Plant Community

•Fields (landscape)

•Crop types

• Chemical use 

pattern

Applications

•Drift model

•Environmental 

conditions

•Habitats (NTTP) 

ibc patches

Exposure

•Dose-responses 

(ecotoxicology)

 individual-level 

effect by species 

and attribute

Individual-level 

Effects

•Empirical 

distribution of 

effects over 

species

by attribute

Species Effect 

Distribution • Assign sensitivity to 

species

• Species effect 

distribution sampling

• Link attributes to model 

parameters

IBC

Plant Populationand Communitylevel Effects

Page 3

Xplicit individual-level effects in space and time IBC
Xplicit (Schad et al.)

Page 4

 Xplicit is a probabilistic modelling approach for estimating 

spatially and temporally explicit exposure and effect based 

on landscape data 

• Consider chemical applications, wind conditions, drift exposure, and effect 

data from standard ecotox. tests (vegetative vigor and seedling emergence) 

to predict plant individual-level effects 

• Simulate a range of complexity levels ranging from simple edge-of-the-field 

to complex landscapes)

• Used in regulatory risk assessments in Europe

1 3 5 7 10 15 20 25 30 40 50 distance from field edge [m]

3 m2 Wind patch 
IBC Model

Page 5

Individuals

Above- and belowground Zone Of Influence (ZOI) 

with overlapping zones*,**

*Weiner et al. 2001 **May et al. 2009

Plant functional types (PFT)

• Growth form

• Plant height

• Clonal reproduction

• Type of CSR-strategist *

• Photosynthetic active area (~SLA)

Spatially explicit (local patch of 3 m2)
IBC Model

- From Real-world to PFT Plant Communities

Page 6

Species/taxa list of interest

e.g.“Calthion“ 

Trait Database (Europe) 

(e.g., BiolFlor, LEDA, CloPla3)

selection of key functional traits, 

(plant size, growth form, resource 

response, seed mass, etc.)

Community

(PFTs)

‘Base' model PFT 

community

IBC model 

initialization

‘Actual' model PFT 

community 

(dynamic)

e.g.,Calthion‘ (≈35 PFTs)

Community

(PFTs)

Vegetation data from field 

and literature (species lists, 

vegetation surveys)

Community

(species list)

 IBC has been validated in predicting plant community dynamics in research projects
Example Community in IBC

Page 7

 Calthion grassland community

• Common in Germany/Europe

• Nutrient rich, moist meadows

• 2 cutting events/year 

• Primula veris potentially endangered 

species included: moderate abundant

PFT richness

year

17

plant (PFT) community initialization

Calthion Community

Population 

PFT1

Ind

1

Ind

2

Ind

i

Population 

PFT 2

Ind

1

Ind

2

Ind

j

Population 

PFT 35

Ind

1

Ind

2

Ind

k
Configuration and Parameterization of IBC

Page 8

 PFT sensitivity assigned randomly or by expert judgment

 Species effect function distribution sampling

• Actual individual-level effect of PFT taken from Species-EffectDistribution

 Linking attributes of species effort to IBC

Vegetative vigor tests: 

biomass, shoot length, 

survival

Seedling tests:

Shoot length, biomass, 

survival, emergence

Biomass gain (plants 

and seedlings)

Mortality probability 

(plants and seedlings)

Probability of 

establishment

IBC

Direct transfer

Species Effect Distribution
Assessment Endpoints (IBC output)

Page 9

Plant 

Community

Population 

PFT1

Ind

1

Ind

2

Ind

i

Population 

PFT 2

Ind

1

Ind

2

Ind

j

Population 

PFT N

Ind

1

Ind

2

Ind

k

• Biomass (total, above- and belowground)

• Number of PFTs

• Number of individuals

• Diversity indices (Shannon, Simpson, Evenness)

• Shootmass

• Number of individuals (= population size)

• Cover

• Quasi extinction risk

(extinction risk, if population size decreases below a 

certain threshold; here: conservative approach: 25% of 

mean population size in control)
Case Study

Page 10

1: Xplicit

a herbicide

• Soybean: 1 x 740 g/ha 

+ 1 x 595 g/ha 

• Dose-responses

• Wind towards NTTP

• Drift predicted by 

AgDrift

• edge of the field 

2: Species Effect Distribution

Plant Community 

Test Patches 

Field-edge distances:

• 3 ft

• 10 ft

3: IBC

Test Plant Community 

(Calthion)

• Two cutting events, low

grazing intensity

• Primula veris (PFT) as 

endangered species and 

assumed high sensitivity

To evaluate drift effects on edge of the field NTTP
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1.0

0.5

1.5

R

elatio

n

T

r

e

atm

e

nt/C

o

ntr

ol

30 years herbicide exposure 35 years recovery

Relation Treatment/Control

 Reduction of biomass and the number of PFTs (PFT richness)

Community Level Effects at Edge of Field (3 ft)
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R

elatio

n

T

r

e

atm

e

nt/C

o

ntr

ol

1.5

1.0

0.5

35 years ‚recovery‘

Relation Treatment/Control

 Only temporary reduction of biomass, and no effect on PFT richness

Community Level Effects at Edge of Field (10 ft)

30 years herbicide exposure
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1.0

0.5

1.0

0.5

1.0

R

0.5

ela

tio

n

T

r

e

a

t

m

e

n

t

/

C

o

n

t

r

ol

30 years herbicide exposure 35 years ‚recovery‘

Inverse Simpson

Eveness

Shannon

 Different response of diversity indices

 Interpretation of the different indices is ongoing

Community Level Effects (3 ft) 
Page 14

Shootmass for selected PFT-types in community context

PFT Carex panicea PFT Cirsium rivulare

PFT Lotus pedunculatus PFT Myosotis nemorosa

0 1 2 3 4

year

0 1 2 3 4

year

R

elatio

n

Tre

atm

e

nt/C

o

ntrol

Population Level Effects (3 ft)
 No effect on field boundary within a 10 ft distance

Page 15

3ft 3ft 3ft

Population Level Effects
Page 16

 High extinction risks for Primula veris (assumed high sensitivity) at the field 

edge for isolated populations

 Population recovers when degree of isolation is low

 Low risk for Primula veris populations at 10 ft distance

Degree of isolation

High (low seed input) Medium Low (high seed input)

3ft 3ft 3ft

*Quasi extinction risk:

Extinction risk, if population size

decreases below a certain

threshold; here, conservative

setting of 25% of mean

population size in control

Population Level Effects -Primula veris 
Summary

 Xplicit-IBC offers an integrated approach to analyze impacts of drift to 

individual plants (traits) at community and population levels at 

landscape scale.

 Scenarios with different levels of complexity can be addressed, ranging 

from conservative edge-of-the-field to full landscape-scales

• representing real-world landscapes with specific agricultural and 

management practice and,

• spatial species occurrence with consideration of isolation of plant 

populations

 IBC has been validated in predicting plant community dynamics in 

research projects

Page 17
Ongoing Work

 Additional scenario development based on the established 

framework

• Plant communities, landscape scenario, test patches, herbicide 

use, exposure model, plant species/community occurrence and 

isolation, etc.

 Validation of IBC-grass of predicted herbicidal effects at plant 

community and population level using field data

 Further evaluation of transferring measured individual-level effects of 

species to IBC traits

 Streamline model interface/runs for regulatory use

Page 18
Thank you!