Forest-hydrological Study on Transpiration in a Mountainous Watershed

为了更详细地描述森林蒸腾作用，尝试在森林流域用三种方法估算山地流域的蒸腾速率。利用短期水量平衡方法和截留雨量观测，估算了基尔余试验流域的年蒸腾速率和月蒸腾速率。本文利用赤松、柏木混交林林冠上方的气象观测资料，利用Penman-Monteith模型估算了松柏混交林的蒸腾速率。在吉林流域气象观测塔周围进行了热脉冲法树液流速测量。利用手持计算机和具有继电器开关输出的A-D转换器组成的自动热脉冲测速系统，连续两年多地测量了热脉冲法树液流速。蒸腾作用Ra…的季节变化特征由这三种方法估算的更多的TE彼此吻合较好。用Penman-Monteith方法和树干液流测量估算的蒸腾作用的日变化也是一致的。然而，用Penman-Monteith方法估计的速率与树干液流测量之间的关系呈现出非线性曲线。造成这种非线性关系的原因可能是由于用一种简单的方法计算的热脉冲速度与实际液流速度之间的非线性关系。为了用热脉冲方法准确地估计蒸腾速率，对一棵柏木采伐后的树木进行了热脉冲方法和吸水率测量的同步观测。用一种简单的方法计算的吸水率与热脉冲速度的关系与Periman-Monteith法和热脉冲法的估计值之间的关系曲线几乎相同。通过对具有实际热脉冲传递条件的对流-扩散方程进行数值计算，可以将这种关系再现为模拟模型。较少

Attempt has been made to estimate transpiration rate from mountainous watershed using three methods in a forested watershed for detail description on forest transpiration. In the Kiryu Experimental watershed, annual and monthly transpiration rate had been estimated by the short term water budget method and intercepted rainfall observation. In this study, transpiration rate has been estimated using the Penman-Monteith model with the meteorological data observed above the forest canopy in a mixed stand of Japanese Red Pine and Japanese Cypress. Measurement of sap flow velocity using the heat-pulse method also has been carried out around the tower for meteorological observation in the Kiryu watershed.Sap flow velocity using the heat-pulse method has been measured continuously more than two years by an automatic heat-pulse velocity measuring system composed of a handheld computer and a A-D converter with relay switch output. The characteristic of the seasonal variations in transpiration ra … More te estimated by these three methods agreed well one another. Diurnal variations in transpiration estimated by the Penman-Monteith method and by the sap flow measurement also agreed well. However, the relationships between estimated rate by the Penman-Monteith method and sap flow measurement shows a non-linear curve. The reason of the non-linear relationships may caused by the non-linear relationships between the heat-pulse velocity calculated by a simple method and the actual sap flow velocity.For the accurate estimation of transpiration rate using the heat- pulse method, simultaneous observation of heat-pulse method and water absorption rate measurement for a cut tree of Japanese Cypress has been conducted. The relationships between water absorption rate and the heat- pulse velocity calculated by a simple method shows is the nearly same curve as the relationships between estimated value by the Periman-Monteith method and the heat-pulse method. This relationships can be reproduced a simulation model using numerical calculation of an advection-diffusion equation with actual heat-pulse transfer conditions. Less