HR: 17:25h
AN: B24C-06    [Abstracts]
TI: Does Hawaiian native forest conserve water? Lower uptake rates at tree and stand scale by Metrosideros polymorpha relative to plantation species
AU: * Kagawa, A K
EM: kagawa@hawaii.edu
AF: Botany Department, University of Hawaii at Manoa, 3190 Maile Way, Honolulu, HI 96822, United States
AU: Sack, L
EM: lawrensack@ucla.edu
AF: Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA 90095, United States
AU: Duarte, T K
AF: Kamehameha Schools, 567 South King Street, Honolulu, HI 96813, United States
AU: James, S A
AF: Pacific Center for Molecular Biodiversity, Bishop Museum, 1525 Bernice Street, Honolulu, HI 96817, United States
AB: Native plants are often claimed to be conservative water users that enhance groundwater recharge compared to faster-growing non-native species that tend to dominate watersheds. This argument would have implications for motivating conservation and restoration of native forest in Hawai'i. However, few studies have examined differences in native and non-native plant transpiration (water use) at species or at stand level. Our aim was determine whether species matter to stand-level water use. We measured plant transpiration in a continuous mosaic of native forest and non-native tree plantation in Honaunau, Hawaii, focusing on endemic dominant tree Metrosideros polymorpha, alien timber trees Eucalyptus saligna and Fraxinus uhdei, and dominant understory Cibotium tree ferns. We measured xylem sap flow for six individuals of each species continuously for over eight weeks, and we estimated stand water use by scaling up these measurements using stand sapwood area and tree fern leaf area values obtained through vegetation surveys. Native forest dominant Metrosideros had the lowest rates of whole-tree daily water use at 8 kg day^-1 (200kg m^-2_sapwood day^-1), less than half the daily rates for Eucalyptus or Fraxinus; Metrosideros also had the lowest maximum transpiration rates of the three tree species. At the stand level, Fraxinus-dominated stands had higher water use than Eucalyptus- and Metrosideros- dominated stands due to the species' high sap flow rates, five-fold greater sapwood allocation, and the stands' two-fold greater dominant tree density. In Metrosideros-dominated stands, high Cibotium tree fern leaf area contributed to nearly 60% of water use, indicating the fern's critical role in forest water balance. Stand water use was influenced by factors at various scales, including species composition, stem density, tree sizes, and tree species' sapwood allocation, and was affected significantly by understory contributions. These findings highlight the importance of constituent species in forest water use, and in the case of this Hawaiian forest, indicate conservative water use by native forest.
DE: 0476 Plant ecology (1851)
DE: 0495 Water/energy interactions (1878)
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1852 Plant uptake
SC: Biogeosciences [B]
MN: 2007 Fall Meeting