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Quantifying the Impacts of High-Priority Non-Native and Dominant Native Plant Species on Freshwater Availability in the State of Hawaii
Phase 1A -- Species Evaluation and Site Selection on Maui

Project Chief: Alan Mair
Project Period: 2016 through 2017
Cooperators: Maui County Department of Water Supply, Hawaii State Commission on Water Resource Management
Collaborator: University of Hawaii at Manoa, Department of Geography
Location: Island of Maui


Because of limited data, current understanding of regional impacts of highly invasive non-native forest species on water resources is incomplete, which is not conducive to developing effective and efficient resource-management strategies. This study addresses a specific need to collect information that will lead to a better understanding of the hydrologic impacts of high-priority non-native plant species on freshwater availability on Maui and throughout the State of Hawaii. The overall objective of this study is to provide needed information for (1) assessing species-specific impacts on freshwater availability and (2) reducing uncertainty in regional recharge estimates associated with forested areas.

The study was developed as an outcome of three workshops and a field reconnaissance related to the study. To accomplish the overall objective, an intensive field investigation will be implemented to quantify plot-scale rates of rainfall, net precipitation, cloud-water interception, evapotranspiration, infiltration, and groundwater recharge for different plant species. The selection of plant species and suitable study sites is a necessary and critical first step towards achieving the overall study objective. Therefore, to address this first step, the study is divided into two phases: Phase 1A, a species-evaluation and site-selection phase, and Phase 1B, an intensive field data-collection phase. Phase 1A is currently in-progress. Phase 1B will be initiated pending the results of Phase 1A and stakeholder interest.


The objectives of Phase 1A are to (1) determine how transpiration rates are dependent on species type within forested areas, (2) determine how understory and overstory forest species influence stand-level transpiration rates, (3) determine how infiltration rates and soil hydrophobicity are dependent on species type, and (4) develop a detailed study plan and proposal for Phase 1B. Phase 1B will involve field monitoring to quantify plot-scale rates of rainfall, net precipitation, cloud-water interception, evapotranspiration, and groundwater recharge for different plant species.

Relevance and Benefits

Quantifying the hydrologic impacts of dominant native and high-priority non-native species is critical for (1) understanding how different vegetation types impact freshwater availability and surface-water runoff, (2) determining how to best measure the impacts of watershed management and restoration on freshwater availability, and (3) properly managing groundwater in the United States. The results of this study will inform resource managers and watershed partnerships in Hawaii of the potential impacts of high-priority non-native species on water resources. By quantifying the hydrologic impacts of dominant native and high-priority non-native species on water resources that provide public-water supply and support fragile ecosystems, this study broadly supports two of the six science directions in the USGS Science Strategy: (1) understanding ecosystems and predicting ecosystem change, and (2) a water census of the United States.


To accomplish the Phase 1A objectives, the USGS will (1) conduct a candidate site review and reconnaissance, (2) collect data to measure transpiration and infiltration rates for selected species and study sites, (3) process and analyze data to accomplish Phase 1A objectives, (4) develop a proposal for Phase 1B, and (5) engage stakeholders and cooperators through presentation of Phase 1A results and a study proposal for Phase 1B.

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Page Last Modified: Friday, 13-Jan-2017 15:20:41 EST