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 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(n 0,N)] determines optimal steady state population level N*, corresponding to N 0.  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 N 0 = 400,000 0 31,295 400,000 100 m N (Stationary) D(N)=$2.74N -> 34,202 trees D(N)=$4.88N-> 28,803 trees

15.  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 Miconia: Results (Low Damages) PV losses for N 0 0 2.8 k 400 k 4.4 m 100 m N (stationary)

16. Miconia policy: status quo vs. optimal (win-win) First period removal cost Annual removal cost PV costs Annual damages NPV damages PV (losses) Status quo $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

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