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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

Project Chief: Alan Mair
Cooperators: Maui County Department of Water Supply, Hawaii State Commission on Water Resource Management Hawaii Division of Forestry and Wildlife
Location: Islands of Hawaii, Maui, Molokai, Oahu, and Kauai


In recent years, Federal, State, and County agencies have invested substantial resources to protect forested watershed areas in the State of Hawaii. Watershed partnerships and other conservation organizations have undertaken a variety of watershed-management and watershed-restoration activities that include controlling the spread of highly invasive non-native forest species. Resource managers are concerned that invasive non-native forest species may reduce freshwater availability. However, studies that quantify rates of net precipitation, cloud-water interception, evapotranspiration, infiltration, and groundwater recharge associated with non-native forest species are limited to only a few species and hydrologic settings. Additional information is needed for a variety of hydrologic settings to understand the regional impacts of highly invasive non-native forest species on freshwater availability.

Because of limited information, current understanding of the 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 collaborative study addresses a specific need to collect information that will lead to a better understanding of the hydrologic impacts of non-native plant species on freshwater availability throughout the State of Hawaii. The results of this study will inform resource managers and watershed partnerships in Hawaii of the potential impacts of non-native species on water resources. Collaborators for this study include the Hawaii Community Foundation and Hawaii Watershed Partnerships who are providing financial and logistical support, respectively.


The overall objective of this study is to provide needed information for assessing species-specific impacts on freshwater availability, and reducing uncertainty in regional recharge estimates associated with forested areas. The study is divided into two phases and specific objectives of each phase include the following:

Phase 1A: Species Evaluation and Site Selection on Hawaii, Maui, Molokai, Oahu, and Kauai

  • Identify high-priority native and non-native species, and candidate study sites on each island
  • Select study sites on each island
  • Determine how transpiration rates are dependent on species type within forested areas on Maui
  • Determine how infiltration rates and soil hydrophobicity are dependent on species type on Maui
  • Identify stakeholder needs and potential funding partners for conducting Phase 1B
  • Develop a detailed study plan and proposal for Phase 1B

Phase 1B: Field Monitoring and Data Collection at Selected Study Sites

  • Quantify plot-scale rates of rainfall, net precipitation, cloud-water interception, evapotranspiration, infiltration, and groundwater recharge for different plant species
  • Provide information for defining future species-specific impacts on freshwater availability and developing a range of plausible management scenarios

Relevance and Benefits

Quantifying the hydrologic impacts of high-priority non-native and dominant 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. 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 U.S. Geological Survey Science Strategy: (1) understanding ecosystems and predicting ecosystem change, and (2) a water census of the United States.


To accomplish the Phase 1A objectives, a collaborative team of researchers from the USGS and the University of Hawaii at Manoa will:

  • Conduct workshops on each island with watershed partnerships and stakeholders
  • Conduct a candidate site review and reconnaissance on each island
  • Collect data to measure transpiration and infiltration rates for selected species and study sites on the island of Maui
  • Process and analyze data from the island of Maui

The research team will use the results from Phase 1A to develop a detailed study plan and proposal for Phase 1B, the intensive field data-collection phase. The research team will also engage stakeholders and cooperators through presentations of Phase 1A results and the study proposal for Phase 1B. Phase 1B will be initiated pending the results of Phase 1A and stakeholder interest.

Scientific Research Team

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