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Changes in Water Flow through Hawaiian Forests due to Invasive Species and Changing Rainfall Patterns

Potential Changes in Infiltration in Hawaiian Forests Caused by Climate Change and Invasive Species


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Precipitation in Hawaiʻi’s higher elevation upland areas provides needed water to both people and ecosystems. Once it reaches the ground, rain can either run off and contribute to water flow in streams, or it can infiltrate into the ground and provide water for plants and recharge aquifers and groundwater. The exact route that water takes is controlled by many factors, including the duration and intensity of rainfall, the topography of the land, soil properties, and vegetation. The introduction and spread of invasive plants and animals in Hawaiian forests, which alters the water-use and soil characteristics of ecosystems, can have large impacts on downstream water users. Increased demand and competition for limited water resources [...]

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Acacia_Koa_in `Ola`a Tract_JimJacobi_USGS_crop.jpg
“Acacia Koa in 'Ola'a Tract - Jim Jacobi, USGS”
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“Wailuku River, Hawaii - Credit: Alan Cressler”
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The overall objective of this work is to understand how rapidly expanding invasive plant population distributions coupled with changes in inter-species competitive dynamics (caused by projected shifting rainfall patterns) will impact water resources into the future. Local studies have highlighted how invasive plants and disturbance of the ground-cover vegetation by feral ungulates may alter soil characteristics critical to determining runoff and groundwater recharge (Perkins et al., 2012, 2014). Other efforts have suggested that invasive species, both plant and animal, have altered whole watershed water balances (Giambelluca et al., 2007; 2008; Strauch et al., in preparation) and possibly landscape groundwater recharge (Engott, 2011; Brauman et al., 2012; 2014). However, a landscape-level understanding of the impact of invasive species on water resources both island and state wide is still lacking. Our proposed work will explore the differences in key soil characteristics that control runoff and groundwater recharge across managed and relatively intact native mesic and wet forest communities. To explore the ecohydrological impact of invasion in these communities, we will conduct similar sampling in disturbed, invasive-dominated community types that most frequently replace the native communities considered. Specifically, we will be measuring Ksat (field-saturated hydraulic conductivity) and soil hydrophobicity. Ongoing and projected climate shifts are expected to directly and indirectly impact runoff/recharge in multiple ways. Based on differential soil characteristics among native and invaded community types considered, climate-based changes in runoff/recharge may be evaluated by integrating our field-data results with maps of baseline and future native-forest distributions (Fortini et al., 2015) and potential invasive species spread (Vorsino et al., 2013, Fortini et al., in preparation).

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Wailuku River, Hawaii - Credit: Alan Cressler
Wailuku River, Hawaii - Credit: Alan Cressler


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  • National and Regional Climate Adaptation Science Centers
  • Pacific Islands CASC

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