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Managing invasive species impacts – feral animals and weeds

Talk presented to weed and feral animal control rangers at Kakadu National Park (4 April 2003)

By Peter Bayliss & Dave Walden

Environmental Research Institute of the Supervising Scientist

Registry File #

1

Seminar outline

Principles of population control to mitigate damage

Using integrated ‘Pest Control’ models Damage-density relationship

Cost-of-control curve

Population growth response

Examples Pigs on Kakadu

Buffalo on Kakadu

Mimosa on Oenpelli

Management & monitoring framework for invasive species

2

Managing invasive species impacts

(ferals & weeds)

THE 3 “TRUTHS” OF POPULATION CONTROL

• All animals have an impact on their environment.

• Damage occurs when that impact causes economic or environmental harm.

• How one defines “harm” depends on how one makes a living.

3

Managing invasive species impacts (weeds & ferals)

Involves making choices– how much management intervention at what cost ($) ?– what benefit is delivered ?

Challenge is to make choices that are– sensible– pragmatic– defensible

Requires benefits & costs to be balanced at least– past focus on “activity-based” management– need new focus on “damage-based” management within a budget– involves complex decision making - need to use modelling tools

Pest control

Pest density

Damagereduction

Economic inputs(costs of control)

Outputs(additional income or

improved public asset)

Benefit/cost analysis

Monetary benefit/cost analysisBenefit maximisationCost minimisation

Pest Control Modelling

4

POPULATION CONTROLHOW TO MANAGE IMPACTS OR “DAMAGE”

• Clearly define damage in first place

• Identify a socially acceptable level of damage & corresponding animal density

• Use modelling tools to improve efficiency of control operations within budgetary constraints – i.e. come up with the hard facts & figures

• There are only 3 key models to use ..........

1. DAMAGE - DENSITY RELATIONSHIP

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12

Pest Density

Leve

l of D

amag

e

Socially acceptable?

Threshold

5

2. COST- OF- CONTROL CURVECHOOSING THE RIGHT “TARGET” DENSITY

Threshold dens ity – where damage firs t occurs or is measurable

Socially acceptable dens ity – damage level

Buffalo – Arnhem Land 1985

3. POPULATION GROWTH RESPONSE

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 2 4 6 8 10 12

Years

Den

sity

fera

l / k

m2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 2 4 6 8 10 12

Years

Den

sity

fera

l / k

m2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 2 4 6 8 10 12

Years

Den

sity

fera

l / k

m2

RECOVERY RATE(usually rapid with pest species)

initial control

maintenance control

6

Helicopter duration (hrs / pig) = Cost $ / killKNP (1998 - 2001)

0.0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500 600 700

Index pig density (pigs shot)

hrs

/ pig

T = 1.9186 D-0.7861

R2 = 73%, R=0.8513n=58, P<0.001

PIG CONTROL – KAKADU – COST CURVE

NB: Still need to add all other costs – ammo, salary etc

Index density needs to be converted to “actual density”

NTU KCTWM FERAL ANIMAL MANAGEMENT CONTRACT KAKADU

• How do Traditional Owners view this “damage”?

• How do they value pigs & buffalo?

• Which cultural resources (assets) are being damaged or at risk? (habitats, species, sacred sites etc)

• How many & where (whose country & responsibility)?

• How do we manage these different views? - what are the “trade-offs”?

7

SIMULATED BUFFALO CONTROL monitoring performance

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 2 4 6 8 10

Years

Dens

ity fe

ral /

km

2rm = 17% p.a.Initial kill 80%maintenance kill 10%Target 2 / km2

7 years to exceed target again

COST-OF-CONTROL OR HARVEST / HABITAT Costs / km2 / yr Total $

Initial cost $36.91 $3,691Maintenance cost $113 $101,709Total cost fo 10 Years $105,400

SIMULATED BUFFALO HARVEST

For BUFFALOYear start 2003Year end 2023Simulation Years 10

Price $/head $150.0

Total Return $243,245Total Cost $105,400Net cost or benefit $137,845

Net annual Return $13,785 p.aTotal annual cost $10,540 p.a.

$ cost helicopter/hr $1,0001,000

6,000

11,000

16,000

21,000

26,000

31,000

36,000

2002 2006 2010 2014

Year

Cost

or b

enef

it ($

)

Total benefits ($)Total costs($)Net benefits ($)

8

But we also need current information on feral animaldistribution & abundance – many methods e.g. aerial

survey (Bayliss 1985)

Blocks

Transects

Buffalo Pigs

Or use methods related directly to control program e.g. Catch-out fisheries method (Pigs – 1999 Kakadu)

"Catch-out" Method

N = 2,674

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000

Sum of previous number shot

New

pig

s sh

ot/h

r

More cost effective – but requires CONSISTENT collection of the RIGHT sort of effort data (time spent searching & killing in an AREA; # killed, #

bullets/kill)

9

RULES OF ENGAGEMENT OF PEST CONTROL

• Keep focused on damage management, not numbers killed

• Searching an area is just as important as killing – e.g 2 pigs killed in a high priority control area (with threatened habitat) is more important that a 1,000 pigs killed in a low priority area.

• A reduced population will quickly recover – control is “forever” - so need a cost-effective maintenance program using the best kill proportion & time interval to keep density below target (e.g. 30% of what’s left every 2 years).

• So absolutely essential that you collect consistent effort & cost data for each control area, to monitor your performance in relation to DAMAGE control.

Pig impacts on EleocharisPhD student Robert Bednarik – NTU

supported by TOs, Parks & Eriss

Eleocharis dulcis -Bunda

10

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 10 20 30 40 50

TIME (YEARS)

POSS

UM

DEN

SITY

(ha

-1) &

HI

NAU

IND

EX (x

10)

POSSUM

HINAU FRUIT

K

Introduced possum in NZ & damage to native forests

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 10 20 30 40 50 60 70 80

YEAR

POSS

UM

& H

INAU

DEN

SIT

Y

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 10 20 30 40 50 60 70 80

YEAR

POSS

UM

& H

INAU

DEN

SIT

Y

Target = 10% reductionTarget = 80% reduction

DENSITY- DAMAGE THRESHOLD

Possums Hinau

What target density is needed to restore natural “masting” cyclein hinau fruit production?

11

Mimosa Risk Assessmentnorthern Australia

Wetlands across northern Australia potentially at risk of mimosa infestation, based on 1:250K topographical wetland data & potential distribution using CLIMEX

Dave Walden et al. (2002): A Risk Assessment of the Tropical Wetland Weed Mimosa pigra in Northern Australia

Potential impact mimosa on magpie geese nest numbers in Top End (1983-1989)

y = - 0.01Area2 + 71.4Area - 35410R2 = 96%, n=6, P<0.01

01000020000300004000050000600007000080000

0 500 1000 1500 2000 2500 3000 3500

Area Floodplain or mimosa (km2)

Tota

l num

ber n

ests

(los

t)

POTENTIAL DAMAGE CAUSED BY MIMOSA TO WATERBIRDS

12

Impact of mimosa on floodplain plant biodiversity (CSIRO study Oenpelli 1993)

Loss = 0.90 MC - 2.81R2 = 90%, n=4, P<0.05

0

20

40

60

80

100

0 20 40 60 80 100

% Cover mimosa

% S

peci

es lo

ss

DAMAGE CAUSED BY MIMOSA TO WETLAND PLANT DIVERSITY

MIMOSA & PARAGRASS DESTROYS BUSHTUCKER HARVESTS

& ANY POTENTIAL FOR COMMERCIAL USE

13

Mapping Paragrass & other weeds on the Magela

New (2003)Old (1991)

Cost-of-control curve MimosaOenpelli 1991 - 1997

y = 30150x-0.7109

R2 = 93%, P<0.001

$0

$100

$200

$300

$400

$500

$600

$700

0 2000 4000 6000 8000

Mimosa control area (ha)

$ Co

st /

ha

Mimosa control on Oenpelli Floodplain

14

MIMOSA CONTROL OENPELLI(1991 – 1997)

0

5000

10000

15000

20000

25000

30000

35000

0 2 4 6 8 10 12 14 16 18 20

Years

Area

mim

osa

(ha)

1991

C osts/h a T o ta l Co sts

In iti a l co st ($ /h a ) $ 0 $ 0M e a n a n n ua l m a in t c ost ($/ h a / y r $ 0 $ 0To ta l co st ( $ /h a ) for $ 0 $ 013 Y e a r s

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 2 4 6 8 10 12 14 16 18 20

Years

Area

mim

osa

(ha)

1991

Costs/ha Total Costs

Initial cost ($/ha) $51 $404,162Mean annual maint cost ($/ha/yr) $218 $247,707Total cost ($/ha) for $1,139 $1,642,696

ABUNDANCE MANAGEMENT FRAMEWORK

ABUNDANCE APPROACHDominates pest control, is a single species, single method & single location approach - inefficient

PIGS CONTROL

DAMAGE(ground disturbance or eat yams)

15

IMPACT MANAGEMENT FRAMEWORK

DAMAGE APPROACHFocus is on the "damage", not the animal; allows use of social & economic values in management decisions - more efficient & realistic

PIGS DAMAGE CONTROL

GROUND SOCIAL & ECONOMICDISTURBANCE VALUES