楠梓仙溪森林土壤種子庫組成之研究

Abstract

土壤種子庫為森林生態系更新之重要環節，亦是森林潛在植物社會。本研究調查臺灣亞熱帶山地雨林之楠梓仙溪森林土壤種子庫組成，配合先前進行的地被組成研究與喬木調查結果，藉以了解土壤種子庫與森林植被之關係，並探討土壤種子庫在森林更新中所扮演的角色。 在2010年2月1日至3日期間，從75個長期監測的小苗動態樣區中鑽取直徑12 cm、深度15 cm的土壤核心樣本。將樣本分成四份，分別為L1層（落葉層）、L2層（深度0-5 cm）、L3層（深度5-10 cm）及L4層（深度10-15 cm）。將每份土壤樣本均勻分散於育苗盤中以利種子萌發，種子萌發後，鑑別物種並計算數量。 截至2011年8月底為止，已萌發之種子共記錄76種植物，數量共計4,790顆，若換算成密度為5,650 m-2，而以L2層之種子密度最高，隨著深度增加種子數亦隨之減少。所萌發之種子多以不耐陰性植物為主，其中又以水麻（Debregeasia orientalis）和賊仔樹（Tetradium glabrifolium）數量最多；在地被或是林冠層占有高優勢度之樹種如長葉木薑子（Litsea acuminata）、假長葉楠（Machilus pseudolongifolia）、長尾尖葉櫧（Castanopsis cuspidata var. carlesii）等未在種子庫中發現其種子。以Motyka’s index計算樣區種子庫、地被組成與冠層樹種之相似性指數，結果發現種子庫與喬木、小苗庫的相似度較低，小苗庫與喬木的相似度較高，意指楠梓仙溪森林中種子庫所代表的潛在植物社會和現存之植被關聯度低。 根據研究結果並配合地面樣區調查及喬木資料，我們可以推論當干擾發生時，耐陰性植物會以林下小苗庫來更新，而不耐陰性植物則是以種子的方式儲藏於土壤中形成土壤種子庫，等待森林孔隙發生以進行更新。

The soil seed bank is an important link in regeneration of the forest ecosystem. It is considered an important potential seed source for the plant communities. The aim of the study is to investigate the composition of the soil seed bank of Nantzuhsienshi forest, a subtropical montane rain forest in Taiwan. We summarized the previous results of the understory and canopy composition, with the aim of understand the relationship between soil seed bank and forest vegetation, and discuss the role of soil seed bank in the forest regeneration. During Feb. 1 to Feb. 3, 2010, the soil samples were collected from 75 quadrats which were set up for monitoring seedling dynamics. For each quadrat, a soil core which diameter was 12 cm and depth was 15 cm was extracted. The soil core was then divided into four parts, namely L1 (litter layer), L2 (depth 0-5 cm), L3 (depth 5-10 cm) and L4 (depth 10-15 cm). Each part of the soil samples was evenly placed in a trap for seed germination. The species and abundance of seedlings were recorded. So far, seventy-six species were germinating. 4,790 seeds were recorded, and the average seed density was 5,650 m-2. Seed highest density was L2 layer, the number of seed was decrease with increase of depth. Most species from the seeds in soil seed bank were shade-intolerant species. Debregeasia orientalis and Tetradium glabrifolium were the most abundant species in the soil seed bank, which is incongruent with the understory and canopy composition reported in the previous study. The dominant species in understory or canopy layer e.g. Litsea acuminata, Machilus pseudolongifolia and Castanopsis cuspidata var. carlesii, we found no seeds in soil. Using Motyka’s index to calculate the similarity of soil seed bank, understory and canopy composition. Result indicated that the similarity indices between soil seed bank and understory seedling or canopy species were lower. The similarity indices between seedling and canopy species was higher. Means that the relational degree between potential plant community and existing vegetation was low in Nantzuhsienshi forest. According to the result of research. We can inferred that when disturbances create sites for generation, shade-tolerant species will regenerate from understory seedling. Shade-intolerant species can store seeds in soil, waiting for the occurrence of forest gap and regeneration.