Control of Invasive Species: Lessons from Miconia in Hawaii

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Control of Invasive Species Lessons from
Miconia in Hawaii

• Kimberly Burnett, Brooks Kaiser,
• Basharat A. Pitafi, James Roumasset
• University of Hawaii, Manoa, HI
• Gettysburg College, Gettysburg, PA

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Objectives

• Inform public policy decisions for invasive
  species using economic theory
• Optimal control of an existing invader
• Case study from Hawaii

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Our case
Existing invader Miconia calvescens
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Minimize NPV (Costsdamages)

• NPV of reducing population to N consists of
• 1. Transition cost of reducing the population
  from
• to
• 2. Cost of maintaining population at
• 3. Damages incurred from remaining at

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Minimize NPV (Costsdamages)

• NPV of increasing population to N consists of
• 1. Transition damage associated with this time
  and popn level
• 2. Cost of maintaining population at
• 3. Damages incurred from remaining at

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An Algorithm for Minimizing Costs Damages
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Existing invader methodology

• Choosing MinV(n0,N) determines optimal steady
  state population level N, corresponding to N0.
• N minimizes costs and damages over time and
• may be smaller (including zero) than the
  existing population
• or larger (including carrying capacity) than the
  existing population
• Is potentially dependent on the current invasion
  level

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Case Study

• Growth function g(N)
• Damage function D(N)
• Control cost function C(N,x)

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Miconia Growth

• b, intrinsic growth rate 0.3
• from analysis of the spread of the tree on Hawaii
  since 1960s introduction
• K, carrying capacity 100,000,000
• (100 trees per acre over 1 million acres above
  the 1800 mm/yr rainfall line)

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Miconia Damages

• Endangered birds
• Households willing to pay 31/ bird species /year
  to keep a species from extinction (Loomis and
  White 1996)
• Full threat of loss in biodiversity on all
  islands equivalent to a loss of ½ the endangered
  bird species ? 103-303 mill / year
• Watershed
• Groundwater recharge losses ? 137 million /year
  (Kaiser and Roumasset 2002)
• Increased sedimentation ? 33.9 million /year
  (Kaiser and Roumasset 2000)
• Total damages
• Estimated average of 377.4 million per year
• If any 1 tree equally responsible for its portion
  of damages, per-tree damage rate of 3.77

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Biodiversity
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Ecosystem services
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Miconia Control cost

• Search component
• Treatment component
• 2003 total number of trees controlled on 4
  islands 72,339
• Annual control expenditures 1 million
• 72,339 trees removed thought to be less than ¼ of
  existing population

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Miconia Results (High damages)

• Current stock 400,000
• lt
• Reduce stock to N 31,295 trees, maintain

PV losses for N0 400,000






D(N)2.74N -gt 34,202 trees D(N)4.88N-gt 28,803
trees


0

31,29
5



400
,000



100 m N (Stationary)


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Miconia Results(Low Damages)

• If lower damages,
• Global min at N31,295,
• Local min at N100 m
• Illustrates need to check both above and below
  initial population

PV losses for N0








0

2.8 k

400 k 4.4 m 100 m
N (stationary)

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Miconia policy status quo vs. optimal (win-win)
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Summary

• Status quo policy welfare equivalent of doing
  nothing
• Optimal control of invasive species requires
  integrated assessment of bio-economic threat
• Growth pattern, control costs, and damages must
  be estimated as functions of population and
  removal
• Optimal policies dependent on initial population
  at time of action
• Eradication, internal steady state, accommodation
  all viable outcomes
• Catastrophic damages from continuation of status
  quo policies can be avoided at costs even lower
  than current spending trajectory

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Limitations and direction for further research

• Overall
• Sophistication of growth, control cost functions
• Accurate anticipation of damages, particularly
  ecological
• Seed bank, spatial dimensions improved