| 概要 |
九州大学福岡演習林の御手洗水試験流域においてGranier法を用いて8～20本のヒノキ(Chamaecyparis obtusa)の樹液流速測定を行い,樹液流速および蒸散量の個体差や微気象条件との関係について検討した.樹液流速の日変化は,流速の立ち上がり時間,ピーク時間および停止時間は各試料木でほぼ変わらず,変動パターンに個体差はなかった.樹液流速は大気飽差(VPD)に伴って増加する傾向を示したが...,VPDが約25hPaを超えると樹液流速の増加が頭打ちになった.このようなVPDに対する樹液流速の応答性に個体差は認められなかった.樹液流速は,晴天日においては胸高直径(DBH)が大きいほど増加する傾向があったが,曇天日においてはDBHに関わらずほぼ一定だった,辺材面積はDBHが大きいほど広く,両者には高い相関関係(R^2=0.78)がみられた.単木蒸散量は,晴天日,曇天日に関わらずDBHが大きいほど多く,両者に相関関係(晴天日R^2=0.72,曇天日R^2=0.62)がみられた.これらのことより,単木蒸散量は,DBHが大きくなると辺材面積が増加するだけでなく,樹液流速も増加するため,両者によって相乗的に増加することを明らかにした.調査期間中の林分蒸散量は,Penmanの可能蒸発量と高い相関関係(R^2=O .83)があり,調査期間中に土壌水分の著しい低下はみられなかったことから,主に微気象条件に依存していることが示唆された.
Sap flux densities of Chamaecyparis obtusa were measured by means of Granier method in the Ochozu experimental watershed of Kyushu University Forest in Fukuoka, Japan. Sap flux densities and transpiration rates were compared among different sized trees and the relationship between transpiration rates and climatic factors were discussed. Although sap flux densities significantly differed among the trees, their diurnal variation patterns, such as rise, peak and down time, were similar. Each sap flux density increased with vapor pressure deficit(VPD), but leveled off when VPD exceeded 25hPa. Sap flux densities tended to increase with diameter of breast height(DBH) in fine days, whereas they were similar regardless of DBH in cloudy days. Sapwood area in trees increased with DBH, and a high correlation was shown between them (R^2=0.78). Transpiration rate from a single tree increased with DBH regardless of weather, and high correlations between them were shown on a fine day (R^2=0.72) and on a cloudy day (R^2=0.62). These results indicated that transpiration rate from a single tree increased with DBH due to increase in sapwood area and the increase in sap flux density on fine days. Transpiration rate in the experimental plot was linearly related with Penman's potential evaporation (R^2=0.83). Since soil moisture was adequate during the experimental period, it could be suggested that the weather condition is mainly responsible for the variation of transpiration rate.続きを見る
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