Hydrology of Tropical Montane Cloud Forest in Hawai'i

0309731詹贝卢卡热带山地森林经常有雾，是具有重要水文和生态价值的地区。在云区内，植被从通过的空气中剥离水滴，从而增加水分输入。 由于云水拦截和抑制蒸腾作用，它们产生高流域产量，支持下游地区的水资源需求。 在夏威夷，潮湿的山地森林地区是地下水补给的重要来源，也是受威胁的生态资源的所在地。 夏威夷水资源开发和脆弱生态系统保护的规划取决于森林水文过程的准确量化。 然而，在夏威夷的森林中没有直接测量过ET，也没有任何先前的研究集中在由于物种入侵或夏威夷热带山地云雾森林中的其他干扰而导致的附生植物层损失的水文影响上。 最近在类似的海洋热带环境中的研究表明，夏威夷的森林ET可能超过目前的估计265-900毫米yr-1。 在夏威夷准确的森林ET测量是迫切需要的，以测试在其他地方发现的异常高的利率的再现性，并回答有关在夏威夷水文过程的具体问题。 冠层水平衡观测表明，云水拦截可能是负责在夏威夷的水文输入比以前认为的更大的比例。 本项目将有助于更全面地了解热带森林水文学，并通过以下方式满足对夏威夷水文通量进行更准确估计的迫切需要：（1）确定夏威夷潮湿森林地点的蒸散率、蒸腾率、截留蒸发率和土壤/凋落物蒸发率;（2）测定本地林和外来种林分的雾截留、截留蒸发、茎流、茎贮量和蒸腾量;（3）在夏威夷森林试验点测试估算蒸散量的替代方法;（4）在毛伊岛现有观测点使用替代方法估算蒸散量。 为了解决本研究的目标，我们将进行全面的实地测量的水通量的所有组成部分，进出，并在夏威夷岛的两个森林网站的植被层内。 这些地点将包括云区内的原生森林和入侵物种地点。 这项研究将有三个重叠的组成部分。 在第一部分中，将在两个主要实地地点对降雨分配、蒸散、蒸腾和雾截留进行密集监测。 在整个研究的三年期间，将继续进行现场监测。从研究的第二年开始，并在最后一年加强，研究的第二部分将侧重于分析每个站点的总蒸发量和截留蒸发量，物种入侵对雾截留和截留蒸发量的影响，SST变化对这些过程的影响，以及估计夏威夷森林ET的替代方法的性能。 在第三部分中，在前两个阶段获得的知识将被应用到估计ET在夏威夷的地形气候范围内的问题。

0309731GiambellucaTropical montane forests with frequent fog are zones of great hydrological and ecological value. Within the cloud zone, vegetation strips droplets from the passing air, thereby increasing water input. Because of cloud water interception and suppressed transpiration, they generate high watershed yields, supporting water resource needs of downstream regions. In Hawai'i, wet montane forest areas are critically important sources of groundwater recharge and host threatened ecological resources. Planning for water development and protection of fragile ecosystems in Hawai'i depend on accurate quantification of hydrological processes in forests. However, no direct measurements of ET have ever been made in Hawai'i's forests, nor have any prior studies focused on the hydrological impacts of the loss of the epiphyte layer due to species invasion or other disturbances in Hawai'i's tropical montane cloud forests. Recent studies in similar maritime tropical environments suggest that forest ET in Hawai'i may exceed current estimates by 265-900 mm yr-1. Accurate forest ET measurements in Hawai'i are urgently needed to test the reproducibility of exceptionally high rates found elsewhere and to answer specific questions about hydrologic processes in Hawai'i. Canopy water balance observations suggest cloud water interception may be responsible for a larger proportion of the hydrological input in Hawai'i than previously thought. This project will contribute to a more comprehensive understanding of tropical forest hydrology generally, and address pressing needs for more accurate estimates of hydrologic fluxes in Hawai'i, by: (1) determining the rates of evapotranspiration, transpiration, interception evaporation, and soil/litter evaporation for wet forest sites in Hawai`i; (2) determining fog interception, interception evaporation, stem flow, stem storage, and transpiration in native forest and in an alien species stand; (3) testing alternative methods of estimating ET for Hawai'i forest sites; and (4) using alternative methods to estimate ET at existing observing sites on Maui. To address the objectives of this study, we will conduct comprehensive field measurements of all components of water flux into, out of, and within the vegetative layer at two forest sites on Hawai'i Island. The sites will include native forest and an invasive species site, both within the cloud zone. There will be three overlapping components of this research. In the first component, rainfall partitioning, evapotranspiration, transpiration, and fog interception will be intensively monitored at the two primary field sites. Field monitoring will continue throughout the three years of the study. Beginning in the second year of the study and intensifying in the final year, component two of the study will focus on analysis of the total evaporation and interception evaporation at each site, effects of species invasion on fog interception and interception evaporation, influences of SST variations on these processes, and performance of alternative methods of estimating ET in Hawai`i forests. In component three, knowledge gained in the first two phases will be applied to the problem of estimating ET over a range of Hawai'i's topoclimates.