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Economic Currents

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Cost-Effectiveness of Herbicide Ballistic Technology to Control Miconia in Hawaii

UHERO is working with Dr. James Leary (CTAHR) to assess cost effectiveness of Herbicide Ballistic Technology (HBT) operations to control invasive miconia (Miconia calvescens) plants before reaching maturity. Based on studies in Costa Rica, Tahiti and Australia, we can interpret spatial and temporal implications of management driven by miconia’s fecundity, dispersal, seed bank longevity and recruitment. We find that the dispersal kernel of miconia in the East Maui Watershed is closely matched to a similar probability density function developed from miconia naturalized in North Queensland, Australia (Fletcher and Westcott 2013). In this spatial model, 99% of recruitment was within 609 m with rare stochastic events (i.e., 1%) extending out to 1644 m. Based on these biological features, one autogamous, mature plant can impact up to 850 ha (i.e., 2100 acres) of forested watershed with hundreds to thousands of dispersed progeny germinating asynchronously over several decades (Fig. 1).

Figure 1. The dispersal kernel displays as a raster layer creating an 850-ha area calculation with corresponding probability density function (color shades).

Effective management is achieved when target mortality outpaces biological recruitment. Cacho et al. (2007) coined the term ‘‘mortality factor’’ described by the simple equation: m=Pd x Pk, where the probabilities of detection (Pd ) and kill (Pk)are equal determinants of the “mortality” product. Our current Pk is 0.98 for all HBT treatments. With this effective and reliable treatment technique, management outcomes largely depend on detection (Leary et al. 2013; Lodge et al. 2006). Koopman (1946) introduced the mathematical framework for estimating the probability of detection: Pd=1-e-c, where the probability of detection asymptotically approaches 1.0 with increasing coverage (Fig. 2). In operations, imperfect detection can be compensated by frequent interventions compounding coverage levels over time, but with obvious diminishing returns (Leary et al. 2014).

Figure 2. Probability of detection (blue) and the inverse for the equally important confirmation of no targets (orange). Note gray dash connotation of a theoretically “perfect” sensor, where coverage is equal to detection and confirmation.

The variable costs for HBT operations (e.g., flight time and projectiles) are driven by target density (Leary et al 2013, Leary et al. 2014). With that knowledge, we estimate the cost to manage the area (i.e., 850 ha) impacted by the dispersal of new progeny created by a mature plant. A new mature miconia with two panicles may produce ~300-400 progeny. With a single, incipient target being such a high risk, intensive efforts should be matched to comprehensively search the entire impact area over the several decades with a level probability of detection (and equal confirmation of no targets) of all progeny recruits. For instance, with 320 propagules dispersed, Pd would need to exceed 0.9968 with coverage at 5.77 s per 100 m2 pixel totaling ~136 hours of effort over the entire impact area over four decades (Fig. 3A). Any level of coverage less than that (including 99%) would be prone to missing a target that ultimately reaches maturity and newly replenishes the seed bank (Fig. 3B). Furthermore, an overwhelming majority of search effort would actually be dedicated to the confirmation of no targets, where, for instance 87% of effort is invested in looking for 1% of the targets dispersed out to the perimeter.

Figure 3. (A) Search effort (EFT; hours) over a 43-year period to match the level of coverage with the probability of detection from a random search effort. (B) is the reproduction of 2nd generation progeny by undetected targets of the 1st generation shown as Base 10 log scale.

Based on this model, we estimate accrual of future management costs ranging from $169,000-337,000 for every mature target detected, with the increase from the base cost dependent on increasing propagule loads and the static cost to treat each those individuals detected.

- James Leary, Kimberly Burnett and Christopher Wada



Cacho, O.J., Hester, S. and Spring, D., 2007. Applying search theory to determine the feasibility of eradicating an invasive population in natural environments. Australian Journal of Agricultural and Resource Economics, 51(4), pp.425-443. 

Fletcher C. S. and Westcott D. A.. 2013. Dispersal and the design of effective management strategies for plant invasions: matching scales for success. Ecological Applications 23:1881–1892. 

Koopman, B.O. (1946). Search and Screening. Operations Evaluations Group Report no. 56, Center for Naval Analyses, Alexandria, VA. 

Leary, J.J., Gooding, J., Chapman, J., Radford, A., Mahnken, B. and Cox, L.J., 2013. Calibration of an Herbicide Ballistic Technology (HBT) helicopter platform targeting Miconia calvescens in Hawaii. Invasive Plant Science and Management, 6(2), pp.292-303. 

Leary, J., Mahnken, B.V., Cox, L.J., Radford, A., Yanagida, J., Penniman, T., Duffy, D.C. and Gooding, J., 2014. Reducing nascent miconia (Miconia calvescens) patches with an accelerated intervention strategy utilizing herbicide ballistic technology.

Lodge, D.M., Williams, S., MacIsaac, H.J., Hayes, K.R., Leung, B., Reichard, S., Mack, R.N., Moyle, P.B., Smith, M., Andow, D.A. and Carlton, J.T., 2006. Biological invasions: recommendations for US policy and management. Ecological Applications, 16(6), pp.2035- 2054. 

Cost-Effectiveness of Controlling Invasive Miconia via Herbicide Ballistic Technology

Miconia calvescens is an invasive tree native to South and Central America that grows up to 50 feet with shallow root systems that promote erosion. The trees form thick monotypic stands, shading out native plants and threatening the watershed function of Hawaii’s forests. The quick growing miconia can mature in four years and produce 3 million seeds several times a year. It is thought that these seeds can remain viable for at least 18 years, and possibly much longer, before sprouting, potentially many more. Birds spread the tiny seeds when they eat the fruit, as do people when contaminated dirt or mud sticks to shoes, clothing, equipment, or vehicles.

Above: Herbicide is delivered via small purple pellet. Average treatment is 25 shots per plant.
Photo credit: Kimberly Burnett

Miconia was introduced to Maui in the early 1970s at a private nursery and botanical gardens near Hana, and now occurs in approximately 37,000 acres throughout East Maui. Maui Invasive Species Committee (MISC) has been managing Miconia for the last two decades, primarily through the use of ground crews and aerial treatment via long-line spray ball. Herbicide ballistic technology (HBT) was recently developed by Dr. James Leary (CTAHR, UH Manoa) as a way to complement these management strategies. The HBT platform delivers small amounts of herbicide into plant tissue from the air, allowing management in otherwise inaccessible locations. The herbicide is delivered via a small projectile fired from a device similar to a paintball gun.

Above: Getting a first-hand look at HBT operations in East Maui. L to R, Christopher Wada (UHERO), James Leary (CTAHR), Kimberly Burnett (UHERO).  Photo credit: Kimberly Burnett

UHERO’s Project Environment will be working with Dr. Leary to assess the cost-effectiveness of HBT technology relative to other management strategies. Key research questions include how to optimize frequency of surveillance, how to minimize the cost of reducing the population to a target level, where to focus HBT efforts (low density, isolated, high elevation/rainfall areas), and how to best combine HBT with other management strategies for maximum cost effectiveness.

--Kimberly Burnett and Christopher Wada


For more on the economics of Miconia from UHERO, see:

Economic impacts of non-indigenous species: Miconia and the Hawaiian economy

Invasive Species Control over Space and Time: Miconia calvescens on Oahu, Hawaii

Economic lessons from control efforts for an invasive species: Miconia calvescens in Hawaii

Prevention, Eradication, and Containment of Invasive Species: Illustrations from Hawaii

Control of Invasive Species: Lessons from Miconia in Hawaii

An Economic Assessment of Biological Control for Miconia calvescens in Hawaii

Understanding the Links Between Local Ecological Knowledge, Ecosystem Services, and Resilience

UHERO’s Project Environment has received funding from the National Science Foundation to participate in an interdisciplinary, international project that spans the natural and social sciences as well as the terrestrial and marine spheres. UHERO is partnering with scientists, resource managers, cultural practitioners and private landowners in Hawaii and Fiji. The project has two distinct parts; the first examines the relationship between local ecological knowledge and social, economic, and ecological outcomes across twenty rural villages in Fiji. The second part of the project explores the effects of different management and climate change scenarios on ecosystem services and indicators of resilience in three Pacific island watersheds.

For Part 1 of the project, we will focus on twenty rural coastal communities across four districts in Fiji. The team will collect household and village-level data within each of the four districts on ecological knowledge, customary skills and intergenerational knowledge. This will be matched to new and existing data collected from nearby forests and reefs. The goal is to develop an index of local ecological knowledge, as well as an index of social-ecological resilience, and examine relationships between these new indices and other ecological, social and economic outcomes. Of particular interest is the influence of local ecological knowledge on our indicators of resilience.

In Part 2 we will conduct three in-depth case studies at the watershed level, focused on quantifying ecological, cultural, and economic values of various land/ocean uses and covers, and their implications for resilience to climate change. The three watersheds were chosen where collaborators have long-term studies to leverage strong existing relationships with landowners, resource managers and users. The watersheds include Kaupulehu on the leeward coast of Hawaii Island, Haena on the north shore of Kauai, and Kubulau on southwestern Vanua Levu.

In each watershed we will collect new terrestrial data on vegetative composition, canopy cover, and indicators of habitat connectivity. Marine ecological surveys will include reef fish assemblages, benthic cover, species composition, biomass, and trophic structure. Ecosystem and cultural services for land and ocean uses will be calculated based on existing data, ecological characteristics, participatory mapping, and interviews.

To understand what combination of land-use practices best enhance social-ecological resilience under different climate change scenarios, we will evaluate the levels and resilience of ecosystem services under multiple future scenarios of climate change and management. These scenarios will represent a range of likely future climates crossed with a range of possible management decisions for each of the three watersheds. After developing an understanding of the ecological, cultural, and economic benefits of each of the management scenarios, we will then assess the costs of various management regimes under different climate change scenarios. The team can then identify a series of “optimum” scenarios – those that appear to maximize resilience indicators and emphasize the cultural, economic and ecological values identified to be of interest to the community members, land managers, and other stakeholders.

Our dual focus on Hawaii and Fiji provides a spectrum of cultural values and land and ocean uses, from functional agroforestry and traditional subsistence fishing in Fiji, to systematic habitat conservation and restoration in Hawaii. As a result, we can capture a wide spectrum of land management paradigms and their potential outcomes under different climate change scenarios, and our results can inform decision making elsewhere in Hawaii, in the Pacific, and throughout coastal areas more broadly.

-Kim Burnett and Cheryl Geslani

How Do We Measure Social-Ecological Resilience?

Two UHERO graduate researchers, Alex Frost and Cheryl Scarton, attended a field course about social-ecological resilience of island systems in Nadave, Fiji. Participants of the field course were students and environmental practitioners from places throughout the Pacifc like Fiji, Vanuatu, Micronesia and the Solomon Islands.

On day three of the field course, the group took an early morning boat ride to Viwa, an island community of 30 households that is largely food and water self-sufficient. The home stay experience immersed participants in a traditional village lifestyle to apply terrestrial and marine survey methodologies learned from previous days.

Based on western standards and traditional economic measure like income, labor, and production, Viwa would be considered impoverished. The residents’ primary income is through selling excess fish and crops at the market and organization of a home stay immersion program. The island has intermittent power at night from a diesel generator, water comes from a thoughtfully engineered catchment system, and the intermittent power limits access to television and Internet.

From a lens that focuses on social and natural capital versus human and financial capital, Viwa is ecologically and socially wealthy. There is strong community cohesion - every Monday is a rotating social work day, where residents take the time to help one family plant, weed or harvest. Everybody shares excess harvest and people have time for leisure and storytelling. They are always joking, laughing and singing. The knowledge of agroforestry and management of fisheries is passed down through observation and application between generations that do not harm the health of the soil and encourages biodiversity, both are key indicators of sustainability.

How resilient is Viwa island? The common definition of resilience is “the capacity of a system to absorb disturbances or shocks and adapt accordingly while still retaining the same function and structure (McClanahan et al. 2012).” Economically speaking, global financial collapse will probably not affect Viwa at all, but the increasing demand of marine resources from Asia is pressuring people to over harvest. Ecologically, it seems the biggest challenge is invasive species, but heterogeneity of the agroforestry system minimizes the spread of pests and disease, compared to monoculture agriculture. Additionally, they have social mechanisms in place to prepare for extreme events like hurricanes. The island is especially vulnerable to sea level rise, coral bleaching, and shifts in weather patterns (such as a long drought). The village residents are working to develop an extensive water infrastructure system in the future to connect water pipes with an adjacent island. Still, the village faces many social challenges. Younger generations are adapting to the expectations of the market economy by working off island, which leads to a loss of traditional ecological knowledge. Concurrently the growing island population requires further clearing of the land for more housing.

 Overall, the week-long intensive field course brought together faculty, students, and experts to disseminate and learn various methods and tools to measure social-ecological resilience. The forum encouraged network building between the University of Hawai’i and University of South Pacific. The variety of perspectives helped increase participant capacity to challenge existing mental models and assumptions. The experience inspired students to develop future interdisciplinary research on island resilience and identify opportunities to mitigate complex challenges that face Pacific nations, like the impacts of climate change.

- Alex Frost and Kim Burnett