| Abstract |
間伐の有無による遮断蒸発量の違いを調べることは，間伐が森林の渇水緩和機能に与える影響を評価するうえで重要であるが，これまでその違いを計測によって調べた例はわずかしかなかった．最近，佐渡・栗田(2004)は，ヒノキ林に無間伐区，12%間伐区，21%間伐区を設定して水収支法から各区の遮断蒸発量を計測した．しかし，その報告における解析は，間伐の有無が比較的長期（月以上の時間スケール）の森林水収支に与える...影響を把握するという目的からすると，遮断蒸発率（遮断蒸発量／林外雨量）の計算方法に問題があり，誤った結果と結論が導かれていた．そこで，本研究はその目的に合った遮断蒸発率の計算方法を採用して再解析することで，結果と結論を修正した．樹冠通過雨量計測期間の林外雨量は1282.2 ㎜，樹冠通過雨量は無間伐区，12%間伐区，21%間伐区でそれぞれ908.3 ㎜，909.2 ㎜，936.4 ㎜だった．樹幹流量計測期間における林外雨量は88.5 ㎜，樹幹流量は無間伐区，12%間伐区，21%間伐区でそれぞれ0.5 ㎜，0.7 ㎜，0.9 ㎜だった．これらのデータをもとにして，無間伐区，12%間伐区，21%間伐区の遮断蒸発率はそれぞれ29.7%，29.9%，28.0%と修正された．修正された遮断蒸発率をもとにすると，間伐の有無による遮断蒸発率の違いは，遮断蒸発計測で発生する誤差範囲内にあることが新たに指摘された．
Though examinations on the difference in rainfall interception evaporation between thinned and unthinned forests are needed for evaluating the effect of forest thinning on the amount of interception evaporation, only a few examinations have been performed. Sado and Kurita (2004) recently examined the difference in interception evaporation between unthinned, 12％ thinned, and 21％ thinned Chamaecyparis obtusa forest plots based on the water balance method. However, data analysis and conclusions of the study were inappropriate from the viewpoint of examining the change in forest water balance at relatively long time scale (> one month) with forest thinning because of the inappropriate calculation method for the interception ratio ( interception evaporation/rainfall) . Applying an alternative calculation method for the interception ratio, this study reanalyzed the data and modified the results and conclusions. According to the reanalysis, incident rainfall integrated for the whole throughfall measurement period was 1282.2 mm and the throughfall amounts were 908.3 mm, 909.2 mm, and 936.4 mm for unthinned, 12％ thinned, and 21％ thinned plots, respectively. Incident rainfall for the whole stemflow measurement period was 88.5 mm and the stemflow amounts were 0.5 mm, 0.7 mm, and 0.9 mm for unthinned, 12％ thinned, and 21％ thinned plots, respectively. Based on these results, the interception ratio ( i. e. , interception evaporation divided by incident rainfall) was calculated as 29.7％, 29.9％, and 28.0％ for unthinned, 12％ thinned, and 21％ thinned plots, respectively. This difference in the interception ratio among plots found in this study was smaller than that caused by measurement error.show more
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