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    Author(s): Jené Michaud; Susan Cordell; T. Colleen Cole; Rebecca Ostertag
    Date: 2015
    Source: Pacific Science. 69(3): 367-383
    Publication Series: Scientific Journal (JRNL)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (735.0 KB)


    In this study we examined historic drought frequency and hydrologic effects of removing invasive plants from one of the few remaining Hawaiian wet lowland forests, near Hilo, Hawai‘i. We developed a conceptual and statistical model of Hilo droughts using historic rainfall and pan evaporation data and discovered that episodes of low soil moisture were most likely from January to March but also occurred in June or July. Field measurements were taken in four pairs of plots. Nonnative woody and herbaceous species were removed from four plots; control plots were undisturbed. Soil water potential measurements documented partial soil drying in control plots, but not removal plots, during droughts with recurrence intervals of 2–3 yr. Drier soils exhibited strong small-scale heterogeneity in soil water potential that presumably reflects macroporosity in the young ‘a‘â lava flow substrate. Transpiration from and rainfall interception by the dense canopy of nonnative species were most likely responsible for drier conditions in control plots. Removal plots experienced changes to shading, midday vapor pressure deficit, albedo, and aerodynamic resistance, but it appears that hydrologic impact of these variables was minor. We suggest that efforts to restore Hawaiian tropical rain forests should consider drought resilience as one objective, among many, of a restoration program. Germinating seeds, shallowrooted saplings and deeper-rooted mature trees may respond differently to hydrologic effects of removing invasive plants.

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    Michaud, Jené; Cordell, Susan; Cole, T. Colleen; Ostertag, Rebecca. 2015. Drought in an invaded Hawaiian lowland wet forest. Pacific Science. 69(3): 367-383.


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    soil water potential, hydrology, invasive species, drought

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