幹流水和穿落水的水量及水質在三種林分的變化

Distribution and Chemical Characteristics of Nutrients in Throughfall and Stemflow of Three Different Stands

本篇是報導關刀溪水源地集水區三種不同林分在二年試驗期間穿落水和幹流水的水量、水質化學濃度及輸入營養鹽的差異。試驗期間穿落水量在杉木林、次生林及天然林分別佔林外降雨量的77%、76%及74%，幹流水量則分別佔林外雨量的14%、5%及3%。雨水的平均pH為4.42，穿落水和幹流水的pH除杉木林外皆比林外雨高，而杉木林幹流水的pH低至3.6。另一方面，杉木林的幹流水電導度卻高達林外雨的6.7倍，和其他穿落水或幹流水只大約增加1.5~2倍明顯高出甚多。營養鹽輸入量在時間和空間上有顯著的變異，穿落水中養分最大輸入量是次生林中的K，高達59.67 kg/ha/yr，同時也分別輸入38.81 kg/ha/yr的SO4和31.01 kg/ha/yr的NO3，幹流水中養分最大輸入量則是杉木林中的K及SO4分別為6.01及13.49 kg/ha/yr。結果顯示，在此集水區內欲探討養分動態時，幹流水的養分輸入（尤其是杉木林）是不容忽略的。 Ionic concentrations and fluxes of precipitation, throughfall, and stemflow were measured during a period of 2 years in three different stands, China-fir (Cunninghamia lanceolata) plantation, secondary hardwood stand, and natural hardwood stand in Guandaushi Forest. The total throughfall was 77 %, 76 %, and 74 % of the precipitation in China-fir plantation, secondary hardwood stand, and natural hardwood stand, respectively. The total stemflow was 14 %, 5 %, and 3% of precipitation, respectively. The average pH of precipitation was 4.42, and the pH in throughfall and stemflow except in China-fir stand was higher than in precipitation. However, the conductivity in stemflow of the China-fir stand exceeded in precipitation by a factor of 6.7, higher than any other throughfall and stemflow, which were only 1.5~2 times higher than in precipitation. The nutrient inputs to the forest floor differs by years and stands. The maximum input to the forest soil by throughfall was 56.67 kg ha-1yr-1 of K under the secondary hardwood stand, together with 38.81 and 31.01 kg ha-1yr-1 of SO4 and NO3, respectively. In stemflow, K and SO4 were the maximum inputs with 6.01 and 13.49 kg ha-1 yr-1 in China-fir stands, respectively, which indicated that stemflow inputs of ions such as these to the forest may be important for studying nutrient dynamics in a forest watershed.

Ionic concentrations and fluxes of precipitation, throughfall, and stemflow were measured during a period of 2 years in three different stands, China-fir (Cunninghamia lanceolata) plantation, secondary hardwood stand, and natural hardwood stand in Guandaushi Forest. The total throughfall was 77 %, 76 %, and 74 % of the precipitation in China-fir plantation, secondary hardwood stand, and natural hardwood stand, respectively. The total stemflow was 14 %, 5 %, and 3% of precipitation, respectively. The average pH of precipitation was 4.42, and the pH in throughfall and stemflow except in China-fir stand was higher than in precipitation. However, the conductivity in stemflow of the China-fir stand exceeded in precipitation by a factor of 6.7, higher than any other throughfall and stemflow, which were only 1.5~2 times higher than in precipitation. The nutrient inputs to the forest floor differs by years and stands. The maximum input to the forest soil by throughfall was 56.67 kg ha-1yr-1 of K under the secondary hardwood stand, together with 38.81 and 31.01 kg ha-1yr-1 of SO4 and NO3, respectively. In stemflow, K and SO4 were the maximum inputs with 6.01 and 13.49 kg ha-1 yr-1 in China-fir stands, respectively, which indicated that stemflow inputs of ions such as these to the forest may be important for studying nutrient dynamics in a forest watershed.