Making a difference for a truly clean,green and sustainable New Zealand

Modelling weed spreadin heterogeneous landscapes

NZIMA weeds workshop17 April 2007

John Kean (AgResearch, Lincoln)Jake Overton (Landcare Research, Hamilton)Peter Williams (Landcare Research, Nelson)Rowan Buxton (Landcare Research, Lincoln)

Overview

• Why model weeds at the landscape scale?

• Modelling weed spread in heterogenous landscapes(e.g. PestSpread v.1)

• Field data formodelling(e.g. hawthorn)

• A model of aweed model

What is a weed?

1. Any plant that is growing where it is unwanted

“A weed is a plant that has mastered every survival skill except for learning

how to grow in rows.” - Doug Larson

“What is a weed? A plant whose virtues have never been discovered.”

- Ralph Waldo Emerson

What is a weed?

1. Any plant that is growing where it is unwanted

“A weed is a plant that has mastered every survival skill except for learning

how to grow in rows.” - Doug Larson

“What is a weed? A plant whose virtues have never been discovered.”

- Ralph Waldo Emerson

2. A town in northernCalifornia

Why model weeds?

(Feedback from DOC, Regional Councils, Biosecurity NZ)

• Prioritise pests and control efforts

• Transparency of decision-making

• Target surveillance

• Optimising control efficacy

• Support national and international cooordination

• Estimate and communicate the difference made

• Identify research needs

Weed prioritisations

• National Pest Plant Accord(http://www.biosecurity.govt.nz/pests-diseases/plants/accord.htm)

• Regional Pest Management Strategies(e.g. http://www.ecan.govt.nz/Plans+and+Reports

/pestAndWeeds/RPMS+2005.htm)

• National Pest Management Strategies(e.g. http://www1.maf.govt.nz/pms/cgi/pms.pl)

Prioritisations are largely subjective:expert opinion + qualitative weed risk assessments

Can we do better?

currentdistribution

potentialdistribution

yr 10

yr 20

yr 30

yr 40

yr 50

currentdistribution

potentialdistribution

local population growth(aging + local reproduction)

dispersal of propagules

storedresources

species distributions current, potential,

pre-calculated

species setup files

e.g. gorse, pinus, old man’s beard

other spatial information

e.g. friction maps for dispersal

demography modules

e.g. annual herb, tree, vine etc

dispersal modules

e.g. wind, bird, water etc

modelling modules

modelcore

modeluser

web server(with GIS)

• species setup file• distribution maps• management file

predicteddistribution maps

PestSpread v.1

± age-dependent seed production

sigmoid localincrease

Demography modules 1

± persistent seed bank

Seedlings Juveniles Adults

Demography modules 2

Seeds

classicaldispersal

kernel

nearest neighbour

Dispersal modules 1

wind ± topography

Dispersal modules 2

water runoff: direction + flow rate

Dispersal modules 3

bird dispersal

= habitat preference+ seed deposition

Dispersal modules 4

Widespread species Limited distribution species

Tree Corsican pine

Pinus nigra

in Twizel

Sweet pittosporum

Pittosporum undulatum

in Kaitaia

Shrub Scotch broom

Cytisus scoparius

in Palmerston North

Spiny broom

Calicotome spinosa

in Palmerston North

Grass Pampas

Cortaderia selloana

in Palmerston North

Pypgrass

Ehrharta villosa

in Palmerston North

Vine Old man’s beard

Clematis vitalba

in Palmerston North

White bryony

Bryonia cretica

in Palmerston North

Case study weeds

Widespread species Limited distribution species

Tree Corsican pine

stage structured

wind

Sweet pittosporum

stage structured

bird dispersal

Shrub Scotch broom

stage structured

neighbour + run-off

Spiny broom

stage structured

neighbour + run-off

Grass Pampas

stage structured

classical kernel

Pypgrass

sigmoid

neighbour

Vine Old man’s beard

stage structured

classical kernel

White bryony

sigmoid + age

bird dispersal

Case study weeds

NEAREST8 dispersal(10% of cover)

SIGMOID local increase

Pypgrass assumptions

Pypgrass predictions

(NB. No seed bank)

Seedlings< 2 yr

Juveniles2 - 14 yr

Adults>14 yr

Corsican pine life cycle

Wind rose for Twizel in Maywhen wind speed > 5 m/s and temperature > 15 °C

Wind dispersal

Corsican pine

Corsican pine predicted % coverfor 2054

Seedling< 1 yr

Juvenile1 – 2 yr

Mature adult vine> 3 yr

Seed dispersal

250 m

Old man’s beard life cycle

Old man’s beard

Old man’s beard predicted % cover

Robust pest prioritisation and risk assessment

= potential distribution (ultimate risk)

+ current distribution (scope for additional damage)

+ change over time (immediacy of risk)

+ management = cost/benefit of action

+ value of affected areas ($$ or NHMS)

+ impact on affected areas

What next?

PestSpreadv.1

PestSpreadv.2

Points to ponder

1. What is the appropriate spatial scale to be working at?

2. Can we just “scale up” from local models?

3. How much detail about the landscape do we need?

4. Can we really see the landscape from a plant's point of view?

5. How does landscape affect competition/invasibility?

6. Can we legitimately extrapolate model results from one landscape to another, or from one species to another?

Aims:

1. To identify the changing drivers determining hawthorn spread

2. To predict hawthorn spread under different landscape and management influences

Study site: Porters pass, Canterbury

Hawthorn ecology: Long-lived, slow to mature Abundant fleshy fruit spread by blackbirds Seedlings only partially grazing resistant

Spread of hawthorn

1908 (WA Taylor glass plate, Canterbury Museum)

1978 (Ian Whitehouse photo)

2005

Sampling hawthorn

The grand-daddy of them all

A successful day in the field

y = 1.26x + 7.70

R2 = 0.81

0

30

60

90

0 10 20 30 40 50

Diameter (cm)

Ag

e (

ye

ars

)

Predicting hawthorn age

y = 7.12e0.28x

R2 = 0.70

0

30

60

90

0 3 6 9 12

Height (m)

Ag

e (

ye

ars

)

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

0

0.04

0.08

0.12

0.16

010

020

030

040

050

060

070

080

090

010

0011

0012

0013

0014

0015

0016

0017

0018

00

Pro

p. o

f 2

00

6 t

ree

s

N

NE

E

SE

S

SW

W

NW

Direction from original tree

Distance from original tree (m)

Hawthorn spread

Pro

po

rtio

n o

f 2

006

tree

s

LandformIntrinsic rate

of increase /yr

Hills 0.0833

Gullies 0.0707

Scarps 0.0662

High terraces 0.1341

Low terraces and riverbed 0.1925

Effects of landscape

1

10

100

1000

1925 1935 1945 1955 1965 1975 1985 1995

Year

Re

lati

ve

no

tre

es

pre

se

nt

Hawthorn invasion

(NB. Log scale)

1

10

100

1000

1925 1935 1945 1955 1965 1975 1985 1995

Year

Re

lati

ve

no

tre

es

pre

se

nt

Phase 1r = 0.036 /yr

Hawthorn invasion

(NB. Log scale)

1

10

100

1000

1925 1935 1945 1955 1965 1975 1985 1995

Year

Re

lati

ve

no

tre

es

pre

se

nt

Phase 1r = 0.036 /yr

Phase 2r = 0.126 /yr

Hawthorn invasion

cessation of burning+ rabbit control

+ fertilisers= blackbird nesting sites

(NB. Log scale)

= ( - )

× [ (+ ) - ]

× [ × - ( - )]

× ( × )

Potential risk of weed

potentialdistribution

feasibility and costof eradication

climatechange

currentdistribution

probability ofnaturalisation

local rateof increase

dispersalrate

propagulepersistence

feasibility andcost of control

impact on invadedecosystems

value of invadedecosystems

economicsocial

environmental

= ( - )

× [ (+ ) - ]

× [ × - ( - )]

× ( × )

Potential risk of weed

potentialdistribution

feasibility and costof eradication

climatechange

currentdistribution

probability ofnaturalisation

local rateof increase

dispersalrate

propagulepersistence

feasibility andcost of control

impact on invadedecosystems

value of invadedecosystems

economicsocial

environmental

needs work

well studied

potential gains

Acknowledgements

Department of Conservation

Graeme Bourdot (AgResearch, Lincoln)

Shona Lamoureaux (AgResearch, Lincoln)

James Barringer (Landcare Research, Lincoln)

Stephen Ferriss (Landcare Research, Lincoln)

Mandy Barron (AgResearch, Lincoln)

Rowan invasion at Tekapo