Hawai'i conservation alliance

Effect Of Native And Invasive Forest Species On Hydrological Components Of Hawaiian Watersheds

Ali Fares, Graduate Program Chair & Associate Prof. of Hydrology, Natural Resources & Environmental Management Dept., University of Hawai‘i – Mānoa
Farhat Abbas, Assistant Researcher, Natural Resources & Environmental Management Dept., University of Hawai‘i – Mānoa

Wednesday, August 3, 10 AM - 12 PM, Ballroom A

Alien Invasive Species (AIS) are serious threats to various ecosystems around the world. In Hawai‘i, this problem is severe: out of approximately 9,900 forest species, 1,240 species are naturalized (Wagner et al. 2005). In some cases, approximately 90 forest species have become invasive (Smith 1985) and affected ecosystem functions (D’Antonio and Dudley, 1995). Gordon (1998) reported that invasion by the evergreen tree (Melaleuca quinquenervia) modified the hydrologic cycle by increasing evapotranspiration (ET) rates compared with native forest communities. Stratton et al. (2000) reported that, in a dry forest on the island of Lana’i, the invasive Christmas berry (Schinus terebinthifolius) had higher rates of water consumption than native tree species. Evapotranspiration from vegetation is the dominant factor recycling more than two-thirds of the precipitation falling on the conterminous United States (Dunne and Leopold, 1978). In humid tropical regions, such is Hawai‘i, ET generally is the main factor that may affect hydrology of an ecosystem. Some of these AIS shade out and out-compete under story native plants for resources such as light, water and soil nutrients; others may alter the hydrology, chemistry, structure, or biological diversity of the landscape. This may results into increased erosion due to suppression of native ground level plants that normally hold the soil. Due to difference in plant canopy and leaf area index, different forest species affect the effective rainfall by altering throughfall and stheflow in different ways.

A clear understanding of the basic hydrologic processes is needed to restore and manage watersheds across the diverse physiologic unit. Hydrologic modeling has become an essential and powerful tool in watershed studies (Graham and Butts, 2005), and perhaps the only way to extrapolate hydrologic experimental finding from small watersheds to large basins and on the regional model. Process based, spatially distributed models are best suited for understanding how different types of watersheds respond to disturbance. It is important to understand how climate change, land use and topography influence hydrologic responses to disturbance at the regional scale for regional water supply and forest management and policy purposes. In this symposium, the key issues related to the effect of invasive and native forest species on hydrological components of Hawaiian watersheds would be discussed.

In addition to academia, this symposium should be of interest to organizations concerned with invasive forest species in Hawai‘i, environmental groups, conservationists, local, state and federal agencies, ecologists, forest resource managers, regulatory agency staff, lawmakers, policy-makers and students who are interested in addressing global climate change.

  • What’s the Fate of a Drop of Water in a Hawaiian Watershed?
    Ali Fares
  • Vegetation Maps for the Hanalei (Kaua‘i) and Kawela-Kamalo (Moloka‘i) Watersheds as a Foundation for Hydrological Research
    Jim Jacobi
  • Transpiration Variability Across Species and Forest Stands in Hawai‘i
    Aurora Kagawa
  • Groundwater Availability Alters Soil Nitrogen Inputs in a Leeward Stand of Kiawe (Prosopis pallida)
    Bruce Dudley
  • Modeling Water Supply and Demand on Maui: Forests as a Land Use Category
    Emily Grubert
  • Cloud Forest Dynamics at Alakahi, Kohala, Hawai‘i
    Eric Hansen

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