颱風頻繁之亞熱帶雨林四種樹營養再吸收之探討

Abstract

颱風是台灣最常見的自然擾動，颱風會造成大量的落葉，落葉會伴隨營養流失及光合作用效能下降。林木在大量落葉後，是否會藉由調整再吸收效率，來補償颱風所造成的營養損失？ 本研究自2010年8月進行至2010年12月，在福山試驗林一號集水區選擇山龍眼、長葉木薑子、綠樟與鋸葉長尾栲等四個樹種，追蹤分析颱風前後其成熟葉、落葉營養動態，以了解颱風如何影響林木再吸收效率的變動。研究期間有兩個中度颱風影響台灣，依次為9/19登陸的凡那比颱風與10月下旬接近台灣的梅姬颱風，兩個颱風皆帶來豪雨，但僅有凡那比颱風有較大風勢。研究結果顯示，兩個颱風對落葉量與再吸收效率造成的影響並不一致，9月的凡那比颱風對福山生態系帶來的影響大於10月的梅姬颱風。非颱風侵襲的11月有另一波落葉量高峰，山龍眼與長葉木薑子在9月凡那比侵襲期間落葉量較大，而綠樟與鋸葉長尾栲在11月的落葉量較大。在營養再吸收率方面，凡那比颱風造成N、K的再吸收效率下降，Ca、Mg再吸收效率上升，但對P再吸收率影響不大；另外梅姬颱風對營養再吸收效率沒有明顯的影響。追蹤颱風過後的數週，N再吸收效率沒有回升，顯示福山林木對應頻繁擾動，不會以耗費能量增加再吸收效率的方式來補償生長，以避免枝葉又受到不可預期擾動打落而失去更大量的營養。不同樹種在颱風與非颱風期間的落葉量有很大差異，且即使在非颱風期間亦有很大的差異，因此在討論颱風與非颱風期間的再吸收時，宜針對不同樹種分別採樣，才不會因物種間落葉量及再吸收的差異模糊了颱風對再吸收的影響。P再吸收效率與再吸收度皆高於N，顯示P是福山生態系的限制因子。

Typhoon is the most common natural disturbance in Taiwan. Typhoon disturbance often caused high quantity of leaflitter accompanied by the loss of nutrients and reduced photosynthesis. Will the damaged trees adjust nutrient retranslocation to enhance photosynthesis and as such compensate typhoon damage? We studied the pattern of retranslocation of Helicia formosana Hemsl、Litsea acuminata (Bl.) Kurata , Meliosma squamulata Hance , and Castanopsis cuspidata (Thunb. ex Murray) Schottky var. carlesii (Hemsl.)Yamazaki cf. sessilis (Nakai) Liao in Watershed #1 of Fushan Experimental Forest between August and December 2010 which includes period before and after typhoon disturbance. Two typhoons affected Taiwan during the study period, one is typhoon Fanapi landed Taiwan in 19 September 2010 and typhoon Megi approached Taiwan in late October 2010. Both typhoons brought large amount of precipitation but high winds only occurred when typhoon Fanapi affected Taiwan. The result indicates that the two typhoons affected Fushan Experimental Forest differently with typhoon Fanapi had a greater impact than typhoon Megi. There was another leaflitter peak in November unassociated with typhoon disturbance. Helicia formosana and Litsea acuminata had high quantity of leaflitter following typhoon Fanapi whereas leaflitter of Meliosma squamulata and Castanopsis cuspidata peaked in November. In terms of nutrient retranslocation, following typhoon Fanapi the retranslocation efficiency of N and K declined, the efficiency of Ca and Mg increased and the efficiency of P showed little change. No clear pattern of changes in retranslocation was observed following Typhoon Megi. Several weeks after typhoon Fanapi, N retranslocation efficiency did not return to levels before the typhoon. Possibly the energy consuming retranslocaiton is not preferred at Fushan where typhoon disturbance may occur several times a year as such investment in retranslocation may lead to large nutrient and energy loss. Tree species differed significantly in typhoon versus non-typhoon induced leaflitter and even in different collections in non-typhoon period. The result indicates that species-specific leaf-litter collection is required for a full understanding of typhoon effects on nutrient retranslocation. Both the retranslocaiton efficiency and retranslocation proficiency of P were greater than N indicating that P is a more limiting element at Fushan Ecosystem.