臺灣的生物地理：2.一些初步思考與研究

本文基本上專注於臺灣島的生物地理樣式探尋以及生物地理過程推論、試圖從實際方面初步澄清一些臺灣的生物地理現象並從理論方面初步推究其過程－特別是臺灣島的木本植物相與森林植生的起源與演化。文末附(前文錯誤更正)。正文十一節分別摘要如下:一、蘭嶼及綠島的植物相地理:我簡要地評議或檢討了蘭嶼及綠島的地質史、古地理、植物地理過程、植物相地理研究史、以及植物地理研究展望。我認為在研究介於菲律賓群島與日本列島之間的小型島嶼的種子植物相地理時應特別重視植物傳播媒介這個主導性的過程因子、最後建議考慮下面這七群島嶼為獨立的研究分析比較單位:巴布煙群島、巴丹群島、蘭嶼+綠島、先島群島、沖繩群島、奄美群島、大隅群島。二、臺灣島生物相的起源:至少經由一條從越南北部經海南的盛冰期東西向生物傳播“高速公路”以及一條從朝鮮經黃海及東海的盛冰期南北向生物傳播“高速公路”，臺灣這塊陸地在理論上可以在冰期內“得到”大多數在先前的間冰期內存活於大約長江以南的中國東亞季風氣候區內的平地而其傳播又祇能路經乾地或祇能靠限於短距離的傳播方式的陸地生物。三、臺灣島生物相的特色:臺灣島相當高的高等生物種豐富度其實“正常而且自然”。在整個臺灣島生物相裡可能沒有特有屬－不論在高等植物或在高等動物。在臺灣島的高等生物史上似乎未曾發生過明顯的適應性輻射演化過程。絕大多數亞/變種化以及種化似乎發生於生物種的個別族群在冰期/間冰期循環間因某些地理地形與/或氣候因素而被長期隔離的過程中。臺灣地區(包括蘭嶼及綠島)的各門類陸域(包括淡水域)高等生物相在種的階層的特有率平均在10-15%左右。在觸及第四紀種化研究的脈絡裡我進一步建議以一個新的研究方向來擴展東亞－北美之間的植物地理關係這個老論題，因為我認為北亞赤道帶濕潤亞洲與北亞赤道帶濕潤美洲之間生物相的對比應該可以揭露濕潤東亞與濕潤北美之間不是在某個意義上更深一層就是大體而言更古老更久遠的生物地理關係。四、臺灣島的氣候特色:在東亞季風氣候的大格局下，強大的暖洋流黑潮與強大的東亞冬季風在臺灣島附近互相牽扯；我相當詳細地定量分析了在太陽輻射的基礎上冬季風與黑潮“共同決定”臺灣島沿海平地的冬溫的情況。臺灣島上山地的冬温情況非常複雜；東北季風顯著地影響臺灣島中海拔“迎風”山地和低海拔“背風”山地的冬季氣候(尤其是温度氣候)。中央山脈(廣義，包括脊樑山脈、雪山山脈、玉山山塊)的形勢對臺灣島山區的水分氣候及植物覆被的影響極大。我提出了一個以植物指標來初步決定臺灣島山地雲帶的最近千年概略海拔下限的方法。全島平地在冬季可以分成四處氣候區:南端西側(即恆春半島西側)、東岸(包括恆春半島東側)、西岸、及東北岸。在初步分析一些重要的區域性氣候力在冰期內的種種可能變動之後，我以為臺灣島的低海拔地帶在冰期的冬季裡存在三個氣候區：東南部(包括恆春半島東側)、西半部(包括恆春半島西側)、東北部。在兩種第四紀氣候波動階段裡，在臺灣島的低海拔地帶應該(曾經)分別存在兩種氣候地理樣式序列、而臺灣海峽陸橋的變化也應該(曾經)分別出現為兩種自然地理樣式序列。這兩類過渡性樣式在兩種氣候波動階段中當然依時序而分別“組合”成兩種綜合性的“自然環境地理樣式序列”。這兩種自然環境地理樣式序列就是臺灣島的木本植物相與森林植生在數以十計的大大小小第四紀氣候波動階段中的其實經歷的區域性自然環境背景。五、臺灣島上的木本植物群落:臺灣島上最近這一千年來的潛在主要(準)極相木本植物群落類型至少有十四型；各類型都有簡單的說明。在討論了溝谷型雨林與水平降水在植生學上的意義以及中央山區以檜木為特色的針闊葉混交林在植生學上的本質之餘，我表達了若干觀點:颱風的風力對臺灣島上迎風森林的高度很有影響；在漢文化把島上幾乎所有的低海拔準極相林毀除淨盡之前桑科榕屬植物在低海拔地區的個體數及植物量可能並不像今天這樣大；恆春半島東南部低山(如南仁山)較濕潤而且不當風山腹處(海拔200公尺上下)以及蘭嶼海岸林帶(不含)以上300公尺以下地區的原始森林都是亞赤道帶熱段雨林；島上現在有苔林；島上的苔林及硬葉林都急需專門研究；島上現在沒有季風林，雖然現在在西部的海拔極低地區不時可見在半常給林破伐除之後由大量先驅性落葉樹所主宰的半落葉林；臺灣島上近千年來極可能從未存在過作為單純氣候極相植生的稀木草原；臺灣島上現在既不存在苔原氣候也不存在苔原植生。六、臺灣島森林植生的起源與演化:我討論了兩方面與本節標題有關的族群樣式與過程、並提出一些對曾存或現存於臺灣這塊地面上的(古)植物世界中的廣義東亞區系木本植物族群的“命運”的基本推想。臺灣島森林史的“上古”部份被我分成理論上的四期(海岸林期、大量東亞區系樹種開始加入期、大量東亞區系非先驅性亞赤道帶樹種加入並蟄居於臺灣島東南端期、大量東亞區系亞迴歸帶樹種存活於中央縱貫山地期)。最後討論了1)若干氣候環境因子對臺灣島森林的形相與構造演化的可能影響、2)冬冷落葉闊葉樹種在臺灣島的中央山區(廣義)中即使在間冰期內也還有一席之地的可能原因、3)三個關於由東亞區系樹種所組成的島上森林的分類組成的極特出現象。七、臺灣島植物相的主要區劃：(1)就木本廣義東亞區系植物而論，從廣東省南部到廣西省南部的中國大陸沿海地區與臺灣島東南端的低海拔地區之間存在著極強烈的地理親緣。我認為“南海高速公路”對臺灣島木本廣義東亞區系植物相水平分區的形成的影響至少在表面上過於但未必早於“東海高速公路”者。(2)包括蘭嶼及綠島在內的臺灣地區顯然不是一個自然而合理的陸棲生物地理研究單位以及陸棲生物誌單位。簡單地視恆春半島為植物區系交匯區等於無視於恆春半島在臺灣島廣義東亞區系植物的低/中海拔地理樣式和地理過程上的獨特地位和重要性，所以在區劃全島(低海拔)植物相時在觀念上不應考慮恆春半島植物相中的菲律賓區系成份(臺灣島植物相區劃基本原則一)。在恆春半島及臺灣島其他地區都頗有代表的一些東亞區系木本屬中常有一些種或亞/變種在島上祇見於此或祇見於彼，因此可以而且應該根據所有這些種與亞/變種的確切地理分佈來決定臺灣島上的首要(低海拔)植物地理分隔線的最合適位置(基本原則二)。(3)主要根據這兩個基本原則，我把臺灣島劃分成“東南臺灣植物相大區”及“西北臺灣植物相大區”；它們之間大致的分界線自枋山漢口起向東北穿過脊樑山脈主嶺線到脊樑山脈東側、然後一路往北直到清水斷崖之南。這兩個大區之間最明顯的“過渡/接觸”地帶大致在大漢山(浸水營)一帶。西北大區可以再以中央山區雲帶底緣為分隔面次級切割成低海拔區以及高海拔區。八、臺灣島(低海拔)動物相的主要區劃:臺灣地區各門類(廣義)陸棲高等動物相與高等植物相在生物地理占有許多共同特點；對臺灣地區陸棲高等動物相地理的觀察支持上節所舉出之原則一在臺灣島(低海拔)動物相區劃上的適用性。根據白頭鵯臺灣亞種與臺灣鵯的分佈或初級淡水魚的分佈都可以沿著脊樑山脈把臺灣島切割成兩個首要的低海拔動物地理區:東南臺灣大區與西北臺灣大區；這兩個低海拔大區的西界在枋寮、東界在蘇澳。九、脊樑山脈的臺灣島(低海拔)動物地理意義:以平地言，恆春半島極可能自中更新世開始以來就逐漸在自然地理及自然環境上隔離或半隔離於臺灣西半部。早已存在的脊樑山脈顯然在臺灣島的第四紀低海拔高等動物遷徒/演化史上扮演了極為突出的角色，而士文溪口到枋山溪口一帶與蘇花公路南澳－新城段一帶的脊樑山脈是兩道在臺灣島低海拔動物的環島分佈上效應最強的天然障礙。十、臺灣島木本植物相水平分區的形成:(1)以恆春半島為連結點的低/中海拔V字型(東亞區系)植物分佈區(北限大致在北迴歸線附近)樣式清楚而且特有率高、可以在殼斗科及裸子植物的地理情況看得很清楚。這個極突出的植物地理現象的成因極可能跟臺灣島南端與東南部的低/中海拔地區在第四紀內一直比島上別處為暖的冬天以及較鄰近低/中海拔地區為高的冬雨量有關。這V字的右(東)臂最南段(即臺東達仁鄉境內山區)就臺灣全島源自歐亞大陸的植物的保存與/或演化發展而言其重要性僅改於島中央的中/高海拔雲帶區而不在島南端的低海拔恆春半島之下、因而應該成為將來臺灣生物調查研究的重點地區之一。(2)北部(宜蘭北部+臺北北部)、中部(臺中東卯山到南投日月潭一帶)、東南端(指達仁)、與恆春半島是臺灣島上四處最清楚也最重要的低/中海拔塊狀木本(東亞區系)植物分佈區。它們此外還組合成六類水平分佈樣式/型；這些樣式的成因及植物地理意義可以歸納成四種情況:臺灣穗花杉型、單刺栲型、南投柯型+烏來栲型+捲斗椆型、臺灣油杉型。(3)所謂臺灣島南北兩端分佈樣式其實乃由在區系隸屬及傳播方式上都極不相同的兩類植物所共同呈現:大部份是巽他大陸棚－菲律賓區系的海岸林種，小部份是廣義東亞區系的乾地傳播種。這樣分佈的植物種非常少，而且其中沒有臺灣島特有的亞/變種(含)以上實體。這一種極不重要的分佈型最合適的代表無疑是杜鵑(杜鵑型)。(4)我以過程推論來解釋為什麼現在臺灣島上的海拔極低地區－除了本節所談的V字型地區外－特有植物很少、並以桑科為例來瞭解臺灣地區的另外一些基本低海拔植物地理情況。對所有在本節中提到的木本東亞區系植物的祖先族群自其種源範圍內遷進臺灣的可能時期及路徑我都有簡單的推論。十一、臺灣島木本植物相垂直分化的形成:(1)在大概自中更新世開始以來、臺灣的縱貫山地極可能已經形成一條雲帶，這雲帶此後發展成一段永久的垂直隔離區(中央雲帶區)、從而一直在臺灣島上扮演著“保存孑遺”與“促成演化”的雙重生物史角色。臺灣島上最有代表性的樹種當數“雲帶殼斗科”以及“雲帶裸子植物”的種。(2)有些木本東亞區系植物本來就在中央山區雲帶之上或者在傳進後的第一次間冰期內就迅速穿出於雲帶之上，其中若干演化快的有可能到現在已經是新特有種或特有亞/變種。(3)有些很早就從西南側－西側－北側的歐亞大陸板塊傳來的植物極可能其後在東南端+恆春半島以及中央雲帶區這兩處氣候環境分化已相當明顯的生態－地理區之一發生形態與生態分化、最後形成新種或新亞/變種；這類演化的可能例證經舉出。精研一些尚在旺盛演化中的種結以及譜系關係極近的種對可以讓我們對臺灣島木本(東亞區系)植物相在雲帶頂緣以下的全島性水平分區與垂直分化的形成有更進一步的瞭解。(4)有一小類木本東亞區系植物似乎在雲帶以上及以下“以不變應萬變”；這種情況應該可以部份歸因於這些植物在體態及/或生理生態方面極高的遺傳變異能力。(5)本文最佳提出一個論題:臺灣島中央山區的雲帶環境自從在第四紀內形成以來到底以哪些物理環境因子的變動如何在冰期/間冰期循環以及生物遷徒/演化的過程中“終於”“塑造出”現在的帶內森林的形相與構造以及有關的現生生物相的分類組成?

關鍵字

生物地理；植物地理；植物相區劃；木本植物相；動物地理；動物相區劃；臺灣；臺灣島；第四紀；氣候；雲帶；雲林；森林；植生；殼斗科；裸子植物

並列摘要

This article is basically focused on the search of the biogeographic patterns and the inference of the biogeographic processes for Taiwan Island, attempting to clarify preliminarily some biogeographic phenomena pertaining to Taiwan on practical grounds and to infer preliminarily their respective processes on theoretical grounds, particeularly with regard to the origin and evolution of the woody flora and forest vegetation of Taiwan Island. An important errata for my previous, related articles is appended. The 11 sections of text are individually summarized as follows: 1. The floristic geography of Lanyü and Lüdao: For Lanyü and Lüdao I briefly commented on or examined their geological history, paleogeography, phytogeographic process, history of floristic geographic studies, and the prospect of the phytogeographic studies. I took the position that one should pay special attention to the leading process-factor - plant dispersal agent -in the study of the seed-plant floristic geography of the islets situated between the Philippine Islands and Japan Islands, and suggested to consider the following seven islet-groups to be segregate units for study, analysis, and comparison: Babuyan Isls., Batan Isls., Lanyü +Lüdao, Sakishima Isls., Okinawa Isls., Amami Isls., and plant Osumi Isls. 2. The origin of the biota of Taiwan Island: At least by way of a full-glacial E-W ＂organismal dispersal highway＂ running from northern Vietnam through Hainan as well as a S-N-trending one extending from Korea through Yellow Sea and East China Sea, the land of Taiwan could have during glacials readily ＂obtained＂ theoretically most of the terrestrial organisms that had lived during the immediately previous interglacials on the plains roughly south of Changjiang and within the Chinese part of the East-Asian Monsoon Climatic Region and required dryland connection or relied solely on short-distance modes for their dispersal. 3. Some characteristics of the biota of Taiwan Island: The fairly high species richness of Taiwan Island's higher organisms is virtually ＂normal and natural＂. It is likely that there exist no endemic genera of higher plants or higher animals on Taiwan. No adaptive radiation was definitely detected from within the history of the higher organisms of Taiwan Island. The vast majority, if not all, of the cases of (sub)speciation seem to have occurred in individual populations long isolated during glacial/interglacial cycles because of some geographic, topographic, and/or climatic factors. The species-level endemism rates of the biotas of the major categories of higher terrestrial (including freshwater) organisms native to the Taiwan Region (including at least Lanyü and Lüdao in addition) are on average ca. 10-15%. In the context that touches upon the Quaternary speciation study I further suggested to expand the conventional topic on the floristic relationship between East Asia and North America to cover a new ＂area＂, because I considered that the comparison between the humid Northern Subequatorial biota of Asia and America may reveal either in some sense deeper or overall more ancient biogeographic relationship between humid East Asia and humid North America. 4. The characteristics of the climate of Taiwan Island: In the context of the East- Asian Monsoon Climate, Kuroshio, a powerful warm ocean-current, wrestles with the powerful East-Asian Winter Monsoon in the vicinity of Taiwan Island; I analyzed quantitatively the condition that on the basis of solar radiation the Winter Monsoon and Kuroshio ＂decide hand in hand＂ the winter temperature of the coastal lowlands of the Island. In the montane region of the Island, the variation of winter temperature is highly complex; the northeast monsoon influences significantly the winter climate, particularly the temperature-climate, of the mid-elevational ＂windward＂ montane region and the low- elevational ＂leeward＂ montane region. The physiography of the Central Range s.l. (including the Backbone Range, Xüeshan Range, Yüshan Massif) significantly influences the moisture-climate and plant cover of the mountainous region of Taiwan Island. For a preliminary determination of the approximate lower limit of the montane cloud zone/belt in Taiwan during this millennium I proposed a plant-indicator method. During winter, the lowland area of the whole Island may be subdivided as four climatic regions: the western side of the southernmost end (i.e., the western side of Hengchun Peninsula [HP]), the eastern coast (incl. the eastern side of HP), the western coast, and the northeastern coast After analyzing preliminarily the various possible changes of a certain major regional climatic forces during glacials, I considered that during glacial-winters there might have existed three climatic regions in the lowlands of Taiwan Island: the southeastern part (incl. the eastern side of HP), the western half (incl. the western side of HP), and the northeastern coast. In the two sorts of Quaternary climate-fluctuation stages (Cooling Transition. Warming Transition), there should have existed two sorts of ＂sequence of climatic-geographic patterns in the lowlands of Taiwan Island, and the change of Taiwan-Strait Landbridge should also have appeared as two sorts of ＂sequence of natural geographic patterns＂. In climate-fluctuation stages, these two sorts of transitional patterns would certainly have combined as two sorts of ＂sequence of the geographic patterns of natural environment＂ in time order- these two sorts of sequences were just the regional natural environmental background against which the woody flora and forest vegetation of Taiwan Island have indeed experienced during the dozens of Quaternary elimate-fluetuation stages of varying dimensions 5. The woody plant communities on Taiwan: On Taiwan, within this millennium there exist at least fourteen major types of potential (quasi-) climax woody plant communities; these were briefly discussed. Along with the discussions on the significance of the gully-type rain forest and horizontal precipitation in vegetation science and that on the vegetational nature of the Chamaecyparis-featured mixed coniferous and broadleaved forests in the Central Range s.l., I expressed some viewpoints: the power of typhoon exerts great impact on the height of the windward forests on Taiwan prior to the nearly complete destruction of quasi-climax lowland forests by Han culture, the individual number and phytomass of the plants of Ficus (Moraceae) growing in lowlands might not have been so large as what we see today; the primeval forests growing in the moister and sheltered areas (ca. 200 m a.s.l.) within the low-lying mountains (such as Nanrenshan) in southeastern HP and those appearing higher than the littoral forests but below 300 m a.s.l. on Lanyü Island are hot-Subequatorial rain forests; there exist mossy forests on Taiwan; both of the mossy forests and sclerophyllous forests on Taiwan need study badly; there are no monsoon forests on Taiwan, although in the area of very low elevation on western Taiwan one nowadays fairly often encounters semi-deciduous broadleaved stands dominated by deciduous pioneers thriving after the cut-over of semi-evergreen forests; it is highly possible that within this millennium savanna, as a pure climatic climax vegetation, has never developed on Taiwan; on current Taiwan there exists neither tundra climate nor tundra vegetation. 6. The origin and evolution of the forest vegetation of Taiwan Island: I discussed the population patterns and processes of two aspects related to the title subject of this section, and presented some basic ideas regarding the ＂fate＂ of the woody EAP populations that live or had lived in the plant world of the land of Taiwan. The earlier part of the forest history of Taiwan Island was here theoretically divided into four stages 1) littoral forest stage, 2) stage of the recruitment of a great deal of East-Asian Phytontic tree species, 3) stage of the recruitment of a great deal of non pioneer Subequatorial EAP tree-species and their confinement within the southeastern tip of Taiwan, 4) stage of the survival of a great deal of Subtropical EAP tree species in the Central Montane Region of Taiwan. I finally discussed 1) the possible influences of some climatic elements on the physiognomic and structural evolution of Taiwan's forests, 2) the possible reasons for the survival and local abundance of cold deciduous trees in the Central Montane Region even during interglacials, 3) three very prominent phenomena about the floristic composition of those Taiwan's forests comprising EAP tree-species. 7. The primary division of the flora of Taiwan Island: 1) Insofar as woody EAP plants are concerned, there exists a very strong phytogeographic affinity between the southern coastal lowlands of China Mainland from southern Guangdong to southern Guangxi and the lowland at the southeastern tip of Taiwan Island. I considered that the influence of the South China Sea Highway＂ on the horizontal regionalization of the woody EAP flora of Taiwan Island was at least superficially stronger but not necessarily earlier than that of the ＂East China Sea Highway 2) The Taiwan Region is obviously not a natural and reasonable unit for the biogeographic studies of terrestrial organisms, Viewing HP as simply representing a contact/confluent zone between the EAP and Philippinean Phytont is no less than being blind to the unique status and importance of HP in the low/ middle elevational geographic patterns and processes of the EAP plants on Taiwan; therefore, one in concept should not take into consideration the Philippinean Phytontic elements present in HP's flora when dividing the (low-elevational) flora of Taiwan Island (Basic Principle for the floristie division of Taiwan Island). Within some woody EAP genera that are rather well represented in both HP and the remaining part of Taiwan Island, there are some species or subspecies/varieties that on Taiwan occur only in one of these two regions; it thus becomes highly desirable to determine the primary phytogeographic demarcation line on (lowland) Taiwan on the basis of the precise distribution of all these entities (Basic Principle 2). 3) Chiefly by following these two Principles, I divided Taiwan Island into Southeastern Taiwan Floristic Super-district and Northwestern Taiwan Floristic Super-district; their approximate boundary begins from the mouth of Fang-shanxi, going northeastward and striding the main divide of the Backbone Range to reach the eastern side of the Range, then running northward until ending at the southern side of Qingshuei Cliff. The most prominent contact/confluent zone between them lies around Dahanshan (Jinshueiying) and Guzilunshan. The Northwestern Super-district may be subdivided into Low-elevational District and High-elevational District along the bottom margin of the cloud belt in the Central Range. 8. The primary division of the (lowland) fauna of Taiwan Island: In Taiwan Region, the faunas of the major categories of higher terrestrial animals share a lot of interesting biogeographic traits with the floras of higher plants; such zoogeographic observations strongly suggest that the Basic Principle 1 established before is also suitable for the (lowland) faunistic division of Taiwan Island. It was found that either the distribution of a pair of closely related resident birds (Pycnonotas taivanus, P. sinensis formosae) or that of primary freshwater fishes leads to the same division of the lowland Taiwan into two primary low-elevational zoogeographic regions along the Backbone Range: Southeastern Taiwan Faunistic Super-district and Northwestern Taiwan Faunistic Super-district, with their western boundary at Fangliao of Pingdong and eastern boundary at Su'ao of Hualian 9. The significance of the Backbone Range in the (lowland) zoogeography of Taiwan Island: Inasmuch as the lowlands are concerned, it is highly likely that HP had gradually become (semi-)isolated from the western half of Taiwan Island in natural geography and natural environment since the beginning of the Middle Pleistocene. The long-existing Backbone Range has apparently played a very prominent part in the Quaternary migratory/ evolutionary history of the Island's lowland-living higher animals. That part of the Backbone Range in the general region between the river mouths of Shiwenxi and Fangshanxi and that part along the Nan'so-Xincheng section of Su'ao-Hualian Road were suggested to have functioned as two most effective natural barriers for the islandwide distribution of the Island's lowland-living animals. 10. The horizontal regionalization of the woody flora of Taiwan Island: 1) The HP-based V-shaped low/middle-elevational distribution district (northern ends approaching the Tropic of Cancer) for the woody (EAP) plants on Taiwan assumes a distinct geographic pattern and shows a high endemism rate, as so elegantly exemplified by Fagaceae and gymnosperms. This highly outstanding phytogeographic phenomenon is very likely causally associated with the persistently higher lowland winter temperature in the southern tip and southeastern part of the Island than in the Island's remaining part as well as the higher lowland winter rainfall in this southern area than in the adjoining low-middle elevational areas, both in Quaternary. For the importance of the reservation and/or evolutionary development of the Island's plants taking origin from the Eurasian Continent, the southernmost section of the right (eastern) arm of this V-shaped district (i.e., the mountainous area of Daren of Taidong) was here considered to be most likely second only to the centrally-located middle/high-elevational cloud belt but no inferior to the lowland HP at the southernmost tip of the Island; this area should consequently be highlighted in future islandwide biological surveys. 2) The Northern area (N Yilan + N Taipei), Central area (from Dongmaoshan to Riyuetan), Southeastern tip (i.e., Daren), and HP are the four most distinct and also most important low/middle-elevational woody (EAP) plant distribution blocks on Taiwan. They, in combinations, further exhibit six horizontal distribution patterns. As to the formation and phytogeographic significance of these patterns, four categories can be distinguished: Amentotaxus formosana type, Castanopsis carlesii sessilis type, Lithocarpus nantoensis type + Castanopsis uraiana type + Cyclobalanopsis pachyloma type, and Keteleeria davidiana formosana type. 3) The so-called southern-northern-tip plant distribution pattern on Taiwan is in fact jointly displayed by two sorts of plants different in phytontic origin and dispersal mode; the majority are littoral species from the Philippinean Subphytont of the Sunda-Shelf Phytont while the minority the dryland-dependent species from the EAP. Species so distributed are very few in number, and of them occur no endemic taxa at or higher than the subspecies/ variety rank. Nonetheless, the most suitable representative of this comparatively least important horizontal distribution pattern is Rhododendron simii. 4) By way of inference on process I tried to explain why there exist very few endemic plants nowadays in the very- low-elevational area of Taiwan Island except within the V-shaped district discussed before. I also tried to explore some other basic low-elevational phytogeographic conditions taking Moraceae as an example. For all of the woody EAP plants named in this section, the possible timing and routes of the immigration of their ancestral populations from their outside-Taiwan source areas were briefly inferred individually. 11. The vertical differentiation of the woody flora of Taiwan Island: 1) It is highly likely that since about the beginning of the Middle Pleistocene a cloud belt has formed within the longitudinally-oriented mountain-chains of Taiwan (＂Central Cloud-belt Region＂, CCBR), which has subsequently developed as a permanent vertical ＂isolating zone＂ and in so doing has been playing a double biological role of ＂reserving the old＂ and prompting the new on the Island. The most representative tree-species on Taiwan are apparently those of ＂Cloud-zone Fagaceae＂ and Cloud-zone gymnosperms＂ 2) Some woody EAP plants might have in the beginning lived above the top margin of the rudimentary cloud belt or have after their arrival rapidly ascended above the cloud belt during the first interglacial to come; of them, some fast-evolving ones may appear as new endemic (sub)species today. 3) Some immigrants coming very early from those parts of the Eurasian Plate to the southwest, west, and north had most probably accumulated morphological and/or ecological differentiations in one of the two ecological geographic regions of the Island (Daren+HP, CCBR) that had already been fairly well differentiated in climatic environment, and finally evolved into new (sub)species; possible examples of this sort of evolution were suggested. Detailed studies on some actively evolving species-complexes and some species-pairs composed of closely related species may provide us with a better understanding of the islandwide horizontal regionalization and vertical differentiation of the woody (EAP) flora of Taiwan Island below the top margin of the Central Range cloud belt. 4) A few woody EAP plants seem to have stayed almost unchanged both above and below the CCBR in the drastically-fluctuating Quaternary environment. This might be partly attributable to their high ability in genetic variation in habit and/or physiological ecology. 5) A final topic to raise: How and by way of change of which physical environmental factors had the cloud-zone-environment in the Central Range finally shaped the physiognomy and structure of the current cloud-zone-forests as well as the composition of the related living biota during the recurrent glacial/interglacial cycles and biotic migration/evolution since its formation in the Quaternary?

並列關鍵字

biogeography ； climate ； cloud forest ； cloud zone ； Fagaceae ； faunistic division ； floristic division ； forest ； gymnosperms ； phytogeography ； Quaternary ； Taiwan ； Taiwan Island ； vegetation ； woody flora ； zoogeography

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臺灣的生物地理：2.一些初步思考與研究

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