溪頭人工枯落物不同樹種與養分之動態變化

森林枯落物是森林養分循環的重要過程，也是評估森林生產力的重要指標。本研究以溪頭自然教育園區為試驗地點，利用大面積(100 ha)網格樣點的設置，進行兩年 (2015年 – 2016年)的枯落物收集，主要目的為了解枯落物季節與植生種類的差異，並評估枯落物量與林分特性間的相關關係。調查結果顯示溪頭自然教育園區平均年枯落物量為3867 ±1663 kg ha-1，不同植生種類間，以柳杉、台灣杉與紅檜人工林樣區枯落物量相對較高，年枯落物量介於4123 – 4702 kg ha-1間，明顯高於復育闊葉林年枯落物量790 ± 640 kg ha-1，草坪區幾乎無枯落物收集。在不同部位枯落物中，以葉部枯落物所佔比例最高，佔總枯落物量比例70 %，繁殖體部位所佔比例次高，繁殖體部位枯落物以柳杉人工林所佔比例最高。不同月份枯落物量間，以颱風期間的枯落物量最高，2015年與2016年的颱風事件分別帶來2707 ± 1699 kg ha-1與1938 ± 1185 kg ha-1總枯落物量，佔全年枯落物量的66 %與53 %。個別樣點年枯落物量與鄰近林分結構有顯著相關，就所有樣點而言，當鄰近林分林齡愈大、林木平均DBH、樹高與材積量愈高時，樣點枯落量也愈高。不過，去除不同植生影響後，柳杉林人工林年枯落物量僅與林分材積量呈顯著相關，當鄰近林分材積量愈大，其林木生物量不僅較高，收集枯落物量也相對較多。相較過去研究，本研究更完整地評估溪頭自然教育園區枯落物動態與枯落量，一方面在於較多的採樣數量，另一方面在於隨機網格採樣點的設置，網格採樣方式降低人為設置樣點的偏差。枯落物碳濃度大部分枯落物碳濃度介於45 %與47 %間。氮、磷、鈣、鎂與鉀養分濃度則在不同部位與不同植生間，呈現較大的差異。在不同部位間，以小枝條枯落物的養分濃度最低；不同植生間，鈣濃度以針葉樹枯落物高於闊葉樹枯落物，鎂及鉀濃度則以闊葉樹枯落物高於針葉樹枯落物。柳杉、台灣杉與紅檜有較大的元素回歸量，復育闊葉林除鉀元素回歸量與這些人工林相當外，其他元素回歸量則小於針葉樹人工林。

關鍵字

溪頭；人工林；枯落物；季節變化；養分回歸量

並列摘要

Litterfall is an important process of forest nutrient cycling and anindicator for assessing forest productivity. In this study, the litterfall was collected using a grid sampling set over a large area (100 ha)from 2015 to 2016 in the Xitou Nature Education Area. The main objectives were to assess the differences of litterfall in different seasons and vegetation types and to estimate the relationship between annual litterfall amount and stand characteristics. The results showed that the total amount of annual litterfall was 3867 ± 1663 kg ha-1 in the Xitou Nature Education Area. The amounts of annual litterfall in Japanese cedar Cryptomeria japonica), Taiwania cryptomerioides and Chamaecyparis formosensis stands, ranged from 4123 – 4671 kg ha-1, were relatively higher than those in the restored broadleaf (790 ± 640 kg ha-1) and meadow sites. There was almost no litterfall collection in the meadow sites. The proportion of leaf litterfall was the highest component, accounting for70% of total litterfall. The proportion of propagule litterfall was the second highest component, in which the Japanese cedar stand had a relatively higher proportion than other vegetation types. The highest amount of monthly litterfall occurred during the typhoon events. The typhoon events in 2015 and 2016 brought the total litterfall amount to 2707 ± 1699 kg ha-1 and 1938 ± 1185 kg ha-1, accounting for 66 % and 53 % of total annual litterfall, respectively. The amount of annual litterfall was significantly correlated with the nearby stand characteristics. For all sites, the nearby stand with older stand age and higher mean diameter at breast height, tree height and volume, the higher amount of annual litterfall it was. After removing the effects from vegetation types, the amount of annual litterfall in Japanese cedar stands was only significantly correlated with the stand volume. When nearby stand volume was larger, not only the biomass of the trees was higher but also the amount of annual litterfall. Compared with past studies, the study comprehensively assessed the litterfall dynamics and amounts in the Xitou Nature Education Area, because of more sampling sites and the grid sampling set that may reduce the bias from sampling. Litterfall had 45 % – 47 % C concentration. The other elemental concentrations were variable among the different components and vegetation types. The elemental concentrations of branches showed the lowest, and the coniferous stands had higher Ca concentrations than broadleaf stands while the broadleaf stands had more Mg and K concentrations. Japanese cedar (Cryptomeria japonica), Taiwania cryptomerioides and Chamaecyparis formosensis stands had large nutrient return. In the restored broadleaf, every nutrient flux was lower than coniferous stands except for the nutrient flux of K.