臺灣北部福山地區亞熱帶雨林凋落物之研究

Abstract

福山地區位於臺灣東北部，為一低海拔亞熱帶雨林，其氣候條件介於典型熱帶與四季變化相對鮮明的溫帶之間，全年潮濕多雨且每年受到不同程度的颱風侵襲。本研究目的在於了解福山25-ha動態樣區凋落物之植物組成、凋落模式、颱風侵襲的影響程度以及森林地面層的儲存量。 於2002年10月至2004年9月總計2年期間，以50個收集網每週收集凋落物，而後將其烘乾、分類並秤重以記錄各凋落類別與個別物種落葉量。另於2008年5月至2009年2月期間，每季於50個收集網週邊各收取1份地面層凋落物樣本，用於計算森林地面層儲存量。 調查期間內，總計2003年年凋落總量為7.20 t/ha，與世界其他樣區相比，本研究凋落總量稍低於亞熱帶樣區，且近似於熱帶山地雨林。各凋落類別包括落葉4.83 t/ha (67.08%)、枝條1.37 t/ha (19.03%)、碎屑0.63 t/ha (8.75%)與繁殖體0.37 t/ha (5.14%)。全年總量凋落模式呈現雙高峰，分別為3-4月新芽生長季與7-9月颱風季期間。 落葉方面共鑑定出117種植物，分屬於54科90屬。依各別植物之落葉高峰期的不同，可分為5種落葉模式：(1) 3-4月尖峰落葉型：以殼斗科及樟科等樣區優勢樹種為主，屬於新葉生長季期間落葉，而多數為冠層樹種。(2) 4-7月寬峰落葉型：亦為生長季落葉，但物種屬性以次冠層及灌木居多。(3) 10-11月秋冬落葉型：種數最少，且集中在具有明顯無葉期的全落葉物種。(4) 颱風季落葉型：於颱風侵襲期間大量落葉，多為藤本植物。(5) 不規則落葉型：全年無明顯季節性落葉，也以林下物種居多。多樣化的落葉模式顯示在亞熱帶森林中，以各物種為單位可能比整個森林群落更適合用來觀察植物與環境間交互作用的複雜性。 研究期間計有六次颱風侵襲，各別影響程度以杜鵑颱風最高，該颱風過後當週的凋落總量佔全年度總量的22.93%。若進一步區分為不同類別，落葉量佔全年度落葉總量的12.95%，枝條佔57.83%，而碎屑為23.70%。總計6個颱風影響週次的凋落總量佔二年研究期間的25.32%，其中單以枝條凋落量來看，佔研究期間枝條凋落總量的61.31%為最高，其次是碎屑23.32%及落葉16.19%。此顯示颱風最大的影響在於枝條凋落量的大量增加，並改變不同凋落物類別的組成比例。 森林地面層凋落物的儲存量約為3.97 t/ha，包括落葉2.37 t/ha (59.6%)及枝條1.60 t/ha (40.4%)。

Taiwan situates in the transition region between temperate and tropical areas and is disturbed by typhoons every year. The objects of this study were to examine the composition and patterns of litterfall, and to discuss the influence of typhoon disturbance in the Fushan 25-ha Forest Dynamic Plot. Furthermore, the amount of standing crop of forest floor was estimated. Litterfall was collected weekly by fifty traps in Fushan FDP from October 2002 to September 2004. Fifty standing crops of litter on the forest floor were collected around each litterfall trap at 3-month intervals from May 2008 to February 2009. The annual amount of litterfall was 7.00 t ha-1. Comparing with other study sites, the annual amount of litterfall was slightly lower than those of subtropical forests and similar to those of tropical montane forests. Leaflitter accounted for 68.3% (4.78 t ha-1) of the total litter amount, followed by twig (17.3%, 1.21 t ha-1), debris (9.1%, 0.64 t ha-1) and reproductive bodies (5.2%, 0.37 t ha-1). Two main peaks of total annual litterfall were observed. One occurred during spring flushing from March to May and the other one occurred during the typhoon season from July to September. Leaffall of most species peaked during the former period, which is a commonly seen phenomenon in warm temperate evergreen forests. The latter peak was mainly contributed by the increased biomass of twigs. All leaves were weighted and sorted into 117 species, belong to 54 families and 90 genera. The leaffall patterns varied considerably among species and could be grouped into five categories based on their leaf shedding peaks: pattern 1, amount of leaffall peaked during spring (March to April); pattern 2, leaffall peaked during late spring and summer (April to July); pattern 3, leaffall peaked during late autumn (October to November); pattern 4, mass leaffall right after typhoon; and pattern 5, irregularly oscillated amount of leaffall. The diverse leaffall patterns showed that the level of species may be more suitable than community to observe the complexity of the interaction between individuals and environmental factors in subtropical rainforests. Among six typhoons (Morakot, Dujuan, Melor, Mindulle, Aere and Haima) which passed through Taiwan during this two-year study, typhoon Dujuan had the greatest influence on the forest in terms of the amount of litterfall. The weekly amount of total litterfall, leaves, twigs and debris collected right after typhoon Dujuan accounted for 22.93%, 12.95%, 57.85% and 23.70% of the annual total amount (Oct. 2002-Sep. 2003), respectively. Of the amount of litter contributed by the disturbance of six typhoons, the proportion of twigs (61.31%) was greater than that of leaves (16.19%). The result revealed that the influence of typhoons on litterfall was mainly the increase of twig falling. The amount of standing crop of forest floor was 3.97 t ha-1. Leaflitter accounted for 59.6% (2.37 t ha-1) of the total litter amount, followed by twig (4.04%, 1.40 t ha-1).