Invasive species that alter ecosystem structure and function (i.e., “foundational invaders”) are among the primary threats to Threatened and Endangered (T&E) species, particularly on oceanic islands. Department of Defense (DoD) installations on islands are critical to the U.S. military mission and often contain high numbers of T&E species, protected by installation fences from habitat loss, herbivory, and direct exploitation. Charged with simultaneously carrying out training and military readiness activities and protecting federally listed species, installation managers must select and implement invasive species controls that are effective, efficient, and minimize non-target impacts. The objective of this project is to address Statement of Need #RCSON-23-C1 and advance scientific understanding of the changes in distribution, abundance, and population dynamics of invasive species, and their potential foreseeable impacts to military readiness as a result of changes to threatened and endangered species and species at risk. Specifically, the project team aims to use an existing array of invasive species manage/no management plots in the largest DoD installation in Hawaii (Pōhakuloa Training Area [PTA] on Hawai'i Island) to evaluate the impacts of two invasive foundational plant species on six T&E plant species, both currently and within a context of future projected climate change; assess the impact of existing control measures on both focal invaders and T&E species; project future T&E species population trajectories given feedbacks with invaders under various control method scenarios; and develop decision-support guidance for DoD managers selecting invasive species control protocols while adjusting for T&E species requirements and climate change. This work builds on the five-year, recently completed, SERDP-funded study of endangered plant species responses to invasive predators at PTA.

The project team will collect demographic data for two invasive and six T&E plant species in PTA sites where invaders are currently controlled by installation managers and in comparison, sites lacking such controls. The project team will quantify population trajectories of both invasive and T&E species in response to one another, in response to control efforts, and in response to climate-driven fire risk. The work will (a) advance current state-of-the-art demographic modeling to account for multiple interacting species, providing a resource for managers worldwide, and (b) provide decision support for PTA and other resource managers determining when and where to employ invasive species controls. The project team will complete the following tasks:

1. Demographic sampling of target invasive and T&E plant species in manage/no management plots.
2. Development of Integral Projection Models to evaluate population vital rates for target species.
3. Quantification of the link between target plant demographics and invasives, drought, and weed (or invasive plant) controls.
4. Innovation of Population Viability Analyses to evaluate interactive species responses.
5. Quantification of T&E population exposure to invasive species + climate change-driven fire risk.
6. Development of a comprehensive invasive control plan that takes into account effects of competition with T&E species from invaders, non-target effects of weed (or invasive plant) controls, and fire risk.

This ambitious project is made feasible by the previous intensive field work in PTA (beginning in 2015); the familiarity with the focal species and the field site; and the extant relationships with installation managers.

This work will assess the effectiveness, efficiency, and non-target effects of control efforts aimed at suppressing two foundational invasive plant species in Hawaii’s largest DoD installation. The project team will advance upon state-of-the-art population modeling frameworks to innovate new methods of evaluating population trajectories for multiple interacting species. The project team will provide decision-support guidance for DoD and other managers faced with conserving T&E species of various functional groups, managing foundational invaders, controlling fire risk, preparing for climate change, and ensuring military readiness. The project team will produce a User’s Guide, conference presentations, and peer-reviewed publications to assist managers with resource allocation when managing multiple species simultaneously.