Invasive Species

Invasive Species

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Invasive species outcompete native species in disturbed ecosystems, and they pose a number of threats to the Ala Wai Watershed. 1) Compared to native vegetation, invasive plants generally cause more runoff, which pollutes the streams with sediment and 2) reduces the recharge to our groundwater (The Ala Wai Watershed includes the Pālolo and part of the Nuʻuanu sector of the Honolulu Aquifer). 3) Invasive species and in particular albizia trees in the lower latitudes also create more storm damage and debris debris during a flood, because their trunks, branches, and roots are more likely to break off. 4) Feral pigs degrade the forest and their feces pollute the streams, and 5) invasive catfish are the most common invasive fish in the streams, outcompeting the native ʻoʻopu and others that are critical to the balance of our stream ecosystems.

The Ala Wai Watershed Association is a non-profit founded in 1996 that organizes volunteer, community education, and development activities, and conducts streambank restoration and research. This includes testing different restoration methodologies at Paradise Park in Mānoa to determine the impact of invasive vs. native vegetation on sediment runoff into the streams.

Nā Wai ‘Ekolu is a collective of educators from K-12 and higher education institutions along the Mānoa, Pālolo, and Makiki streams, who care deeply for their watershed through monitoring, research, restoration, and curriculum development with their students. This includes removing invasive catfish and improve the habitat for the native ʻoʻopu.

Almost all the upland forest in the watershed is managed by the Department of Land and Natural Resources, Division of Forestry and Wildlife and is designated as State Forest Reserve. Because of its comparatively good condition and lack of funding resources, the upland forest in the Ala Wai Watershed is not currently under active management for feral pig control or invasive management.

The Koʻolau Mountains Watershed Partnership (KMWP) is a voluntary alliance of major public and private landowners encompassing the Ko’olau range. Partners with lands located in the Ala Wai Watershed include DLNR DOFAW and the Board of Water Supply, and to a lesser extent Kamehameha Schools, Lyon Arboretum, and DHHL. The KMWP is one of multiple Watershed Partnerships in the State comprising the Hawaiʻi Alliance of Watershed Partnerships (HAWP)  whose kuleana span across property boundaries to preserve watershed function and address the invasive species that threaten the health of native Hawaiian forests.

The Lyon Arboretum Botanical Garden in Mānoa, run by the University of Hawaiʻi, offers not only research projects on native Hawaiian plants, conservation biology, and Hawaiian ethnobotany, but also community education and volunteer activities, as well as annual plant sales.

In 2018, the Hawaiʻi Invasive Species Council (HISC) released the Strategic Plan for the Control and Management of Albizia in Hawaiʻi that  provides a framework to minimize the impacts of albizia on the environment, human health, and infrastructure.

The AWWC’s Working Group on Environmental Quality, Research and Science helps connect partners and activities in the Ala Wai Watershed that work on invasive species issues to identify priority areas and share best practices.

Cover photo credit: Nā Wai ʻEkolu and ʻIolani School

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