Rainfall partitioning and cloud water interception in native forest and invaded forest in Hawai'I Volcanoes National Park

摘要

In many Hawaiian forests, including cloud forests, native plant communities are being displaced by invasive tree species,npossibly affecting rainfall partitioning and direct harvesting of cloud droplets by vegetation. In this study, the hydrologicalnimpacts of invasive species are examined, using measurements of rainfall (RF), throughfall (TF) and stemflow (SF), andnestimation of wet-canopy evaporation and cloud water interception (CWI) by the canopy water balance approach in bothnnative Metrosideros polymorpha-dominated and invaded, Psidium cattleianum-dominated forests within Hawai‘i VolcanoesnNational Park (HAVO). Canopy water storage capacity was found to be more than twice as great at the native site (1D86 mm)ncompared to the invaded site (0D85 mm). Annual RF, CWI, TF and SF were 3233, 1188, 3700 and 261 mm, respectively,nfor the native site; and 3735, 734, 3033 and 1091 mm, respectively, for the invaded site. Net RF (TF C SF) was 123 andn110% of RF, respectively, at the two sites. Annual evaporation of water from the wet canopy was also greater at the nativensite (464 mm) than at the invaded site (347 mm). Low canopy water storage capacity and the exceptionally high SF total atnthe invaded site are related to morphological characteristics and high stem density of the invasive P. cattleianum tree, whichnfavour efficient transport of intercepted water to the ground via the stems. Despite its more peripheral location near the edgenof the orographic cloud, CWI at the native site was higher. The characteristics of the native M. polymorpha tree may facilitatenmore effective harvesting of cloud water droplets, enhancing CWI at the site. Species invasion results in a lower proportionnof RF reaching the forest floor (110 vs 123%) and becoming available for groundwater recharge, suggesting that invasion bynP. cattleianum may have significant negative effects on Hawai‘i’s aquatic ecosystems and water resources.