台灣北部福山地區蕨類植物之分佈與環境因數之關係探討，並以蕨類植物作為微環境指標之研究

Abstract

蕨類植物在森林分層結構中，多半隸屬於地被層成員；由於並非森林主要生產者，加上在經濟價值上尚待開發，故在一般植被調查中經常被忽略。然而蕨類植物在森林地被層中的空間分佈和族群密度，不僅能影響森林上層樹種更新的成敗，而且在整個森林能量與養份循環上扮演相當重要的角色。由於蕨類植物在其繁衍過程上，需要周遭微環境中的水份作為其授精作用的媒介，加上其薄小的配子體對於棲地環境的特殊需求（其最適生長條件往往不同於孢子體，故常能決定該種對生存環境的耐性範圍），所以蕨類植物對於各類環境因數的作用及微環境的變異，具有相當高度的敏感性。在生態研究上，受調地區之蕨類植物多寡及其分佈狀況常能對在當地植被、氣候以及環境方面提供相當重要的資訊與証據。 本研究選擇在台灣北部福山地區天然闊葉林中，隨海拔高度650m上升至1200m處進行取樣調查，共設置70個10×10m2的樣區，每一樣區由四個5×5m2的小區所組成。主要以線截法調查樣區內地被植物之覆蓋度及組成，並同時記錄所有胸高直徑（DBH）大於1公分，高度2m以上的喬木種類、覆蓋度與出現層級。所有的數據資料經由雙向列表法（TWINSPAN）以及降趨對應分析法（DCA）處理，以冀尋出蕨類植物與環境因數之間的關係；並利用蕨類對於環境變異具有高度敏感的特性，找出對於各種微環境具有指標性的蕨類植物。 經由樣區調查之原始資料統計，在福山地區蕨類植物之重要值（IVI）排序表中，由於前六種優勢種之重要值累積和已超過一半，前十四種優勢種之重要值累積和亦達全部種類總和之四分之三，可見福山蕨類植物之優勢種集中於少數種類。根據福山試驗分所過去之資料算出本區之Ptph－Q＝8.44。然而就1995至1998年台灣大學植物系蕨類研究室於物候研究中所累積的資料來看，種子植物已增至400種，蕨類方面也增加為190種；所以福山地區實際的蕨類商數應為（190×25）／400＝11.86，遠高於台灣本島的4.83。由此可以推論福山是台灣地區少數幾個極適宜蕨類植物生長的地方；蓋因福山地區的植被同時具有亞熱帶及暖溫帶雨林的特性，其蕨類物種繁多是自不待言的。 樣區調查之原始資料矩陣經由DCA之分析後，可以得知影響福山地區植群分佈之主要為地形因數、方位因數、土壤水分因數以及著生植物覆蓋度等項目，而這些因數所控制的效應均為環境中可供利用之水分含量多寡（最終因數）。而福山地區之地被蕨類植物社會亦經由DCA的分析後，可以大略地分出五個主要的蕨類植群型：（星號*代表特徵種或指標植物；其他則為優勢種） <Type I>倒葉瘤足蕨*—生根卷柏—蔓芒萁型（Plagiogyria dunnii* - Selaginella doederleinii - Dicranopteris tetraphyll type）： 本型之環境主要以林冠疏散、坡度略陡、受風影響較強、環境溼度較低之上坡稜線地形為主。 本型之指標植物為倒葉瘤足蕨、華中瘤足蕨、瘤足蕨、錢氏陵齒蕨、深山雙蓋蕨。 <Type II>長柄鳳尾蕨*—鬼桫欏—廣葉深山雙蓋蕨型（Pteris bella* - Alsophila podophylla -Diplazium uraiense type）： 本型之環境主要以溼度略乾至適中之中、上坡地形為主。 本型之指標植物為長柄鳳尾蕨、台東鱗毛蕨。 <Type III>鬼桫欏—德氏雙蓋蕨—廣葉鋸齒雙蓋蕨型（Alsophila podophylla - Diplazium doederleinii -Diplazium uraiense type）： 本型之棲地環境以溼度偏溼之山坡中、下坡處或鞍部地形為主。 本型並無明顯之指標植物。 <Type IV>魚鱗蕨*—川上氏雙蓋蕨—稀子蕨型（Acrophorus paleolatus* - Diplazium kawakamii -Monachosorum - henryi type）： 本型之棲地環境相當特殊，其棲地位置乃在阿玉山西峰山腰約1000?1200公尺處。該型之最大特色在於其雖處海拔較高之山稜上坡處，但是棲地環境中的水分含量卻相當豐沛，蓋因其已跨入暖溫帶之霧林區之故。 <Type V>擬德氏雙蓋蕨*—肋毛蕨*—德氏雙蓋蕨型（Diplazium pseudodoederleinii* - Acranoides festina* -Diplazium doederleinii type）： 本型之棲地為坡度潮溼的溪谷地形。 本型之指標植物為德氏雙蓋蕨型：擬德氏雙蓋蕨、肋毛蕨、台灣兩面複葉耳蕨。 另外值得注意的是，長柄鳳尾蕨雖在本論文被指為第二型（長柄鳳尾蕨—鬼桫欏—廣葉深山雙蓋蕨型）之指標植物，然其在第一型（倒葉瘤足蕨—生根卷柏一蔓芒萁型）之出現亦相當普遍；所以，廣義來說，本種應算是福山地區較乾燥的中、上坡—稜線地形之指標種。此外，貞蕨也有類似的情形；不同的是，該種乃為泛溼地之指標植物，蓋因其在第四型（魚鱗蕨—川上氏雙蓋蕨—稀子蕨型）和第五型（擬德氏雙蓋蕨—肋毛蕨—德氏雙蓋蕨型）之出現程度均相當普遍。 福山蕨類的植群分佈類型與上層喬木樹種之植群型大致上是吻合的；但由於各蕨類植群型依微地形之起伏與微氣候之變化，彼此相互混雜而呈鑲嵌式分佈的現象，這種情形比上層喬木更為明顯且頻繁。故在反應微棲地之變化方面，蕨類植物乃較上層喬木樹種要更為靈敏，也更能凸顯這些變化。

Most of ferns and fern allies occupy the undergrowth of the forest and are just a small part of the total biomass of the vegetation. They are often ignored in the general forest ecological studies just because of their unknown economical values, minor producers and lower biomass. However, the distribution pattern and population density of pteridophytes on the understory not only affect the regeneration of the primary canopy trees, but also play an important roles in the energy flow and nutrient cycle of the ecosystem. Furthermore, the contents of the environmental water participating in the reproductive process and the critical needs for the microhabitats of the gametophytes make pteridophytes have higher sensibility to the environmental change than the upper trees. Consequently, in the ecological researches pteridophytes frequently provide very important informations and evidences about vegetational, climatical, and environmental conditons. In this study, 70 plots (10×10 m2) with a total area of 0.7 ha. were established from alt. 650 m to 1200 m in the original broadleaf forest at Fushan Botanical Garden in North Taiwan. In each plot, the coverage and composition of all understory plants were investigated through line transect method, meanwhile DBH, species, and individual number of all trees higher than 2 m were recorded. Afterwards, all the primary data matrix were analyzed by TWINSPAN and DCA to find out the relationship between the distribution of pteridophytes and environmental factors. Due to the high sensibility to various environmental chacters, indicator ferns to various habitats were selected and discussed. The analysis of the data investigated reveals that the five main vegetation types of the understory pteridophytes distribute masically in the forest of Fushan area. There are: (Star mark * means chacter species or indicator plants, the others represent dominat species.) <Type I>Plagiogyria dunnii* -Selaginella doederleinii-Dicranopteris tetraphyll type: The habitat peculiarities of the type are more incompact canopy, simple stratification, shorter tree, frequently stronger wind, lower environmental water, and often occupying the upper slope or mountain ridges. Indicator ferns are Plagiogyria dunnii Copel., P. euphlebia (Kunze) Mett., P. rankanensis Hayata, Lindsaea chienii Ching, and Diplazium fauriei Christ. <Type II>Pteris bella* -Alsophila podophylla -Diplazium uraiense type: The habitat position of this type is slightly drier medium or upper mountain slope. Indicator ferns are Pteris bella Tagawa and Dryopteris polita Rosenst. <Type III>Alsophila podophylla -Diplazium doederleinii-Diplazium uraiense type: The habitat of this type is often in slightly humid saddle and lower or medium slope. No apparent indicator ferns are found here. <Type IV> Acrophorus paleolatus* - Diplazium kawakamii - Monachosorum henryi type: This type is only found in the mossy forest which situates on higher mountain region from alt. 1100 m in Fushan. High humidity, closed canopy, and high species diversity are the characteristics of this kind of forest. Indicator fern are Acrophorus paleolatus Pichi sermolii <Type V> Diplazium pseudodoederleinii* - Acranoides festina* -Diplazium doederleinii type: This understory type dominates in the lowerland stream side and valley. The habitat chacters are very high humidity, dense canopy, huge trees, and complicated stratification. Indicator ferns are Diplazium pseudo-doederleinii Hayata, Ctenitis subglandulosa (Hance) Ching, and Arachniodes festina (Hance) Ching. Furthermore, among the selected indicator ferns Pteris bella Tagawa and Cornopteris opaca (Don) Tagawa are not only belonging to one habitat. Broadly speaking, P. bella Tagawa prefers to colonize its population on upper slope and shaded mountant ridges, so this species could be seen in the type II and most parts of the type I. Similarly, C. opaca (Don) Tagawa are the indicator of pan-wetland, so it can be find out in both type IV and V. From the previous studies, the original forests of Fushan area can be divided into five types, too. The locations of these forest types generally match with the understory pteridophyte types. Noteworthily, in addition to the slight differences of these types' range between the canopy and lesser layers, all of the fern types however appear in more complicated and more frequent mosaic distribution pattern just dependent upon the local relief of topography and environmental conditions. Therefore, understory pteridophytes indeed have higher sensitivity to the change of environmental gradients and excellent representation in the minor variations of environment than canopy trees.