Hawaiian native forest conserves water relative to timber plantation: Species and stand traits influence water use

Authors

  • Aurora Kagawa,

    1. University of Hawai‘i at Mānoa, Botany Department, 3190 Maile Way, Honolulu, Hawaii 96822 USA
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  • Lawren Sack,

    Corresponding author
    1. University of Hawai‘i at Mānoa, Botany Department, 3190 Maile Way, Honolulu, Hawaii 96822 USA
    2. University of California, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, California 90095 USA
    •  Corresponding author: Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Drive South, Los Angeles, California 90095-1606 USA. E-mail: lawrensack@ucla.edu

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  • Ka‘eo Duarte,

    1. University of Hawai‘i at Mānoa, Botany Department, 3190 Maile Way, Honolulu, Hawaii 96822 USA
    2. Kamehemeha Schools, Land Assets Division, 567 South King Street, Honolulu, Hawaii 96813 USA
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  • Shelley James

    1. Bishop Museum, Natural Sciences, 1525 Bernice Street, Honolulu, Hawaii 96817 USA
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  • Corresponding Editor: F. C. Meinzer.

Abstract

Tropical forests are becoming increasingly alien-dominated through the establishment of timber plantations and secondary forests. Despite widespread recognition that afforestation results in increased evapotranspiration and lower catchment yields, little is known of the impacts of timber plantations on water balance relative to native forest. Native forest trees have been claimed to use water conservatively and enhance groundwater recharge relative to faster-growing alien species, and this argument should motivate native forest preservation and restoration. However, data have been available primarily for leaf-level gas exchange rather than for whole-plant and stand levels. We measured sap flow of dominant tree and tree fern species over eight weeks in native Metrosideros polymorpha forest and adjacent alien timber plantations on the island of Hawai‘i and estimated total stand transpiration. Metrosideros polymorpha had the lowest values of sap flux density and whole-tree water use (200 kg·m−2 sapwood·d−1, or 8 kg/d for trees of 35 cm mean diameter at breast height, D), substantially less than timber species Eucalyptus saligna or Fraxinus uhdei (33 and 34 kg/d for trees of 73 and 30 cm mean D, respectively). At the stand level, E. saligna and F. uhdei trees had three- and ninefold higher water use, respectively, than native M. polymorpha trees. Understory Cibotium tree ferns were most abundant in M. polymorpha-dominated forest where they accounted for 70% of water use. Overall, F. uhdei plantation had the highest water use at 1.8 mm/d, more than twice that of either E. saligna plantation or M. polymorpha forest. Forest water use was influenced by species composition, stem density, tree size, sapwood allocation, and understory contributions. Transpiration varied strongly among forest types even within the same wet tropical climate, and in this case, native forest had strikingly conservative water use. Comparisons of vegetation cover in water use should provide additional resolution to ecosystem valuation and land management decisions.

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