Control of Invasive Species: Lessons from Miconia in Hawaii

1. 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

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

3. Our case Existing invader: Miconia calvescens

4. Minimize NPV (Costs+damages) 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

5. NPV of increasing population to N consists of:: 1. Transition damage associated with this time and pop’n level 2. Cost of maintaining population at 3. Damages incurred from remaining at Minimize NPV (Costs+damages)

6. An Algorithm for Minimizing Costs + Damages

7. Existing invader: methodology • Choosing Min[V(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

8. Case Study • Growth function g(N) • Damage function D(N) • Control cost function C(N,x)

9. 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)

10. 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

11. Biodiversity

12. Ecosystem services

13. 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

14. Miconia: Results (High damages) • Current stock: 400,000 • < • Reduce stock to N* = 31,295 trees, maintain PV losses for N0 = 400,000 D(N)=$2.74N -> 34,202 trees D(N)=$4.88N-> 28,803 trees 0 31,29 5 400 ,000 100 m N (Stationary)

15. Miconia: Results(Low Damages) • If lower damages, • Global min at N*=31,295, • Local min at N*=100 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)

16. First period removal cost Annual removal cost PV costs Annual damages NPV damages PV (losses) Status quo $1 m $1 m $50 m $369.5 m $12.35 b -$12.4 b Opt policy $6.27 m $449,245 $28.7 m $117,982 $7.4 m -$36.1 m Miconia policy: status quo vs. optimal (win-win)

17. 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

18. Limitations and direction for further research • Overall: • Sophistication of growth, control cost functions • Accurate anticipation of damages, particularly ecological • Seed bank, spatial dimensions improved