Hydrology of Tropical Montane Cloud Forest in Hawai'i

[0309731]热带山地森林雾多，是具有重要水文生态价值的地区。在云区内，植被从经过的空气中带走水滴，从而增加了水的输入。由于云水的截留和蒸腾的抑制，它们产生了很高的流域产量，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，也是受到威胁的生态资源的宿主。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对ET进行过直接测量，也没有任何先前的研究集中在夏威夷热带山地云雾林中由于物种入侵或其他干扰而导致的附生层损失的水文影响。最近在类似的海洋热带环境中进行的研究表明，夏威夷的森林ET可能比目前的估计值高出265-900毫米/年。夏威夷迫切需要精确的森林蒸散发测量，以测试在其他地方发现的异常高的蒸散发率的可重复性，并回答有关夏威夷水文过程的具体问题。冠层水分平衡观测表明，在夏威夷，云水拦截可能比以前认为的要占更大比例的水文输入。该项目将有助于更全面地了解热带森林水文，并通过以下方式解决更准确估计夏威夷水文通量的迫切需要：(1)确定夏威夷潮湿森林地点的蒸散速率、蒸腾速率、截流蒸发速率和土壤/凋落物蒸发速率；(2)测定原生森林和外来树种林分的截雾量、截雾蒸发量、茎流、茎库和蒸腾；(3)对夏威夷森林立地估算ET的替代方法进行测试；(4)利用替代方法估算毛伊岛现有观测点的ET。为了实现本研究的目标，我们将在夏威夷岛上的两个森林站点对进入、流出和在植被层内的水通量的所有组成部分进行全面的实地测量。这些地点将包括原生森林和入侵物种地点，都在云区内。这项研究将有三个重叠的组成部分。在第一个组成部分，将在两个主要场址集中监测降雨分配、蒸散发、蒸腾和雾拦截。实地监测将在整个三年的研究期间继续进行。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和拦截蒸发，物种入侵对雾拦截和拦截蒸发的影响，海温变化对这些过程的影响，以及估算夏威夷森林ET的替代方法的性能。在第三部分，在前两个阶段获得的知识将应用于估算夏威夷一系列地形气候的ET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.