森林内外の降水申の養分量について (第2報)

Abstract

1. 1961年6月より, 京大演習林上賀茂試験地で, 林外地の雨, ヒノキ林および常緑・落葉混交広葉樹林の林内雨をあつめ, カリウム・マグネシウム・リン・硝酸態-・アンモニア態 -窒素の濃度と量を測定した。1963年5月までの実験については, すでに第1報に報告した。2. 1962年12月より, 林内雨に樹幹流を加え, 林床に到着する全雨水について, 1964年5月まで測定した。3. ヒノキ林・広葉樹林の林内雨量・樹幹流量と林外地降水量の関係について, 一次の回帰式をえた。広葉樹林では生育期と生育休止期にわけて回帰式を求める必要があった。これによる1年間 (1963年6月 - 1964年5月) の各プロットの降水量は, 林外地1793. 0mm, ヒノキ林内雨1231. 4mm, 同樹幹流103. 8mm, 広葉樹林内雨1015. 0mm, 同樹幹流417. 6mmであった。4. 養分物質によりそれぞれ特徴があるが, 概して, 林外雨量の大きいときには養分濃度は小さく, 林外雨量が小さいときには養分濃度が大きくなり, そのさい林外雨, 林内雨に較べ樹幹流の濃度が高まる傾向が認められた。林外雨量が大きいときには, 林外雨・林内雨・樹幹流の養分濃度の差は明らかではなかった。5. 1年間 (1963年6月 - 1964年5月) に林外降水に含まれた養分量は, カリウム4. 5, カルシウム10. 6, マグネシウム1. 1, リン0. 24, 硝酸態窒素1. 4, アンモニア態窒素2. 1kg/haであった。6. ヒノキ林内雨・樹幹流中の養分合計量はそれぞれ14. 7 (1.6), 18. 3 (1. 7), 4. 6 (0. 4), 0. 14 (0. 02), 2. 1 (0. 2), 4. 9 (0. 5) kg/haで, 広葉樹林ではそれぞれ48. 4 (9. 3), 17. 7 (4. 6), 4. 8 (1. 1), 0, 48 (0. 06), 2. 0 (0. 4), 5. 4 (1. 3) kg/haであった。なお()内は樹幹流に含まれた養分量である。7. 現在まで推定された葉による養分物質の林地還元量と比較すると, カリウムに関しては本実験の林内雨・樹幹流に含まれる養分量のほうが大きいばあいが多かった。このことは森林の物質循環において, 雨水のもつ量的な意味が大きいこと示していると考えられる。

1. Since June, 1961, rainwater has been collected at the Kamigamo Experimental Forest Station of Kyoto University in Kyoto in three types of plots: an open plot, the throughfall (rainwater which has passed through the forest canopy) in a Hinoki (Chamaecyparis obtusa) stand and in a broadleaved evergreen and deciduous mixed stand. The plant nutrient fractions of Potassium, Calcium, Magnesium, Phosphorus, Nitrate-nitrogen, and Ammonia-nitrogen were analysed and studied from these collections. The results of the experiment until May, 1963 have already been submitted in the first report. 2. From December, 1963 to May, 1964, by the addition of the estimation of the stemflow (rainwater which flows down along the stem surface) to the throughfall, all kinds of water which arrived at the forest floor were collected and analysed monthly. 3. It was necessary to devide the year into a leaf period and a leafless period when considering the throughfall and stemflow in the broadleaved stand. Linear regressions were found in each of the relationships between the precipitation in the open plot and the amount of throughfall and stemflow in the two forest stands. By these regressions, the amounts of rainwater in a one-year period (June, 1963-May, 1964) were calculated as follows: (figures in mm), Open plot 1793.0, Hinoki stand-throughfall 1231.4, -stemflow 103.8, broadleaved stand-throughfall 1015.0, -stemflow 417.6. 4. Though each nutrient has its own characteristics which could be described in detail, generally speaking, the plant nutrient concentration was found to decrease as the precipitation increased. In many cases of precipitation of less than 100 mm per month in the open plot, the nutrient concentration of the stemflow in the two stands was higher than that of the throughfall. In cases of precipitation of more than 200 mm, the differences of nutrient cocenaration between the open plot and the througthfall and stemflow in the two stands were not always clear. 5. In the open plot, the annual fall (i. e., June, 1963-May, 1964) of the plant nutrients brought about by rainwater were estimated as follows: Potassium, 4.5kg/ha; Calcium, 10.6; Magnesium, 1.1; Phosphorus, 0.24; Nitrate-nitrogen, 1.4; Ammonia-nitrogen, 2.1. 6. In the Hinoki stand, the annual fall of those plant nutrients brought about by the throughfall plus stemflow were estimated at 14.7 (1.6), 18.3 (1.7), 4.6 (1.4), 0.14 (0.02), 2.1 (0.2), and 4.9 (0.5) kg/ha, and in the broadleaved stand at 48.4 (9.3), 17.7 (4.6), 4.8 (1.1), 0.48 (0.06), 2.0 (0.4), and 5.4 (1.3) kg/ha respectively. Figuers in brackets are the amount of plant nutrients by stemflow. 7. Comparison of the amount of plant nutrients, especially of Potassium, brought about by litterfall obtained by estimations through the reseearching of forest biomass in other forests, in many cases, the amounts brought by throughfall and stemflow were greater than that by litterfall. This would indicate the importance of throughfall and stemflow in the mineral circulation of the forest ecosystem.