Sap flow measurements of red pines: Developments on a horizontal scale

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  • Tsuchiya Akio
    Graduate School of Integrated Arts and Sciences, Hiroshima University

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  • アカマツの樹幹内蒸散流の観測とその面的展開

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Thermal dissipation probes (TDP) were plugged into the stems of red pines at Hiroshima University’s campus in order to calculate hydraulic conductivity. The data were developed to describe sap flow velocity (cm·s−1) and sap flow (l·h−1). The observed results show that except for rainy days when the transpiration dulls, a few litters of sap flow were absorbed up within an hour during the daytime of sunny days, and the amount was dependent on the diameter of the stems. Sap flow decreased to zero at night, and was small in the daytime in winter as well. Among micro-meteorological parameters obtained in the measurements from April to May, the saturation deficit was found out to be related to sap flow. An empirical equation between stem diameter and annual sap flow was calculated, and was employed to estimate the horizontal transpiration in the middle slope of Saijo Basin where the dieback of red pines has been progressing. As a result, horizontal transpiration on the slope was found to be 146,000 m3·Km−2·yr−1, while the transpiration at the mountain ridge with little dieback was about 644,000 m3, and the areal average was estimated to be about 245,000 m3. On the other hand, evapotranspiration was about 384,000 m3·Km−2·yr−1 from rainfall and discharge at the watershed level. It is thought that the difference between the values includes not only the amount of transpiration of hardwood individuals, but also interception loss of rainfall, and transpiration by paddy rice.<br>

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