北臺灣地區歸化豆科植物對於植物群落衝擊之研究

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(1) . Chapter 1. Plant Invasion in north Taiwan: Insights from the Flora of Naturalized Alien Species. 摘要對於未來進一步的研究而言，包含有分類組成、相對覆蓋度、相對頻度、生活型、原產地及原產地之氣候類型等詳盡的歸化植物基本資料是不可缺少的。為深入探討歸化植物的特性，我們建立了下列兩個假說並驗證之：(1) 由於北臺灣擁有多樣的氣候及地形條件，包括熱帶及亞熱帶氣候的低海拔平原及溫帶氣候的高海拔山地，容易受到來自世界各地的外來植物所入侵；(2)在北臺灣地區成功建立族群的大多數歸化植物，其原產地的氣候條件與北臺灣相符合。野外調查部份在北臺灣各縣市進行，利用 1-km2 之網格系統隨機選取 100 個網格做為實驗樣區，在每個樣區中的各種棲地類型隨機選取五至十個不等之 1-m2 樣點，記錄日期、GPS、海拔高度、原生及歸化之植物種類及植物覆蓋度；另外，計算每一種歸化植物的重要值指數(IVI)做為優勢度之指標。調查總共在 2242 個樣點記錄了 12 種棲地類型及 629 種植物，其隸屬於 130 個科及 409 個屬。依據各歸化類群所擁有的物種總數來排序，菊科、禾本科及豆科為最優勢的三個科，旋花屬則為最優勢的屬；此外，依據重要值指數排序，大花鬼針草為 1 .

(2) . 最優勢的歸化物種。就原產地而言，在北臺灣的大部份歸化植物來自熱帶美洲。. 關鍵字：歸化植物、北臺灣、重要值指數、棲地類型. 2 .

(3) . ABSTRACT Regional naturalized flora with detailed information such as taxonomic composition, relative coverage, frequency, life form, and native areas and climates of naturalized species is important and available to further research. To generate better understanding of those characteristics of naturalized species, we developed and tested the following two hypotheses: (1) North Taiwan, as tropical / subtropical in low altitude and temperate in high altitude with diversified terrains and climate, is vulnerable to plant invasions from all over the world; and (2) the majority of successful naturalized species were introduced from areas with climates similar to those prevailing in north Taiwan. The field investigation was carried out in four counties in north Taiwan. By using 1km2 grid systems, one hundred of total grids were randomly selected as the sample areas. Five to ten square meters quadrates of each habitat type; furthermore, were investigated. A total of 2,242 1-m2 quadrats and twelve habitat types were recorded. Plant species and coverage of all native and naturalized species were collected, and IVI values were calculated for each naturalized species for the summary of dominance. A total of 629 species belonging to 130 families and 409 genus were documented. In part of naturalized flora, there were about 80% dicotyledons in species number and 71% herbs in life form. Among these naturalized flora, Asteraceae, Poaceae, and Fabaceae were the most dominant families and Ipomoea was the most dominant genus according to their own species numbers. In addition, Bidens pilosa L. var. radiata Sch. was the dominant naturalized species 3 .

(4) . according to the IVI value. In part of their origins, most naturalized species in north Taiwan were from America in area and tropical in climate.. Key word: Naturalized plant, North Taiwan, IVI value, Habitat types. 4 .

(5) . INTRODUCTION Invasive species have been considered as major threats to ecosystems by altering the soil nutrients, taking over territories, forming monocultures, changing species compositions, etc (Rogers & Leathwick, 1996; Wuerthner, 1996; Jesson et al., 2000; Evans et al., 2001; Wolf et al., 2001). The ways in which invasive species get into native habitats are also frequently discussed (Gelbard & Harrison, 2005; Foxcroft et al., 2007; Foxcroft et al., 2008). According to Pyšek et al. (2004), many environmental and biological barriers have to be conquered for an introduced species to invade new territories successfully. Environmental factors, such as disturbance, usually provide more opportunities for successful invasions (Ross et al., 2002; Hendrickson et al., 2005; Alston & Richardson, 2006). However, disturbance could be an environmental barrier for introduced species to invade places with low intensity of anthropogenic activities or pressures of natural disturbances (Kang et al., 2007; Paiaro et al., 2007; Theoharides & Dukes, 2007). On the other hand, the invaders’ successful establishment and spreading may depend upon other factors as well, such as biological traits and climates (Wu et al., 2004b; Thuiller et al., 2006; Wilson et al., 2007). We assumed that alien species successfully establishing in native habitats might be considered as respective competitors and deserve attentions. Many of the available checklists of alien species are still in the format of simple enumerations containing only names and basic annotations (Lee, 1974; Söyrinki, 1991; Sykes, 1996). Alien floras with 5 .

(6) . adequate information on relative coverage, frequency, distribution pattern around elevation and habitat types are rather rare (Pysek et al., 2004; Silva & Smith, 2004). Plant invasions in different regions are difficult to compare as long as qualified field data of alien species are scarce. This is a serious obstacle in prioritizing eradication, containment, and control activities regarding exotic pests. In terms of alien floras, substantial attention has been devoted to North American areas and European countries, while Asia and neighbouring islands are still understudied (Corlett, 1988; Turner, 1997; Enomoto, 1999; Meyer, 2000). Among Asian regions, Hong Kong (Corlett, 1992), Japan (Enomoto, 1999), Korea (Koh et al., 2000), Singapore (Corlett, 1988), and Taiwan (Wu et al., 2003; Wu et al., 2004a&b; Wu et al., submitted) have compiled floras of alien weeds or naturalized species, but the realistic field data have rarely been focused around these regions. This study presents an analysis of alien flora of outside of cultivation in north Taiwan. North Taiwan, a diverse landscape and rainy region, ranges of zero to 3,500 meters in elevation and contains about twenty important preserved areas, such as Yangmingshan National Park, Chatianshan Nature Reserve, Yuanyang Lake Nature Reserve, Danshuei River Mangrove Nature Reseve, Shuanglianpi Wildlife Refuge, etc. The undulated topography, together with climate variations, results in the diversified habitats of north Taiwan harboring amounts of endemic and rare flora, such as Taiwan Isoetes (Isoetes taiwanensis), Taiwan Beech (Fagus hayatae), Rhododendron pseudochrysanthum, Sparganium fallax, 6 .

(7) . Kandelia candle, etc (Huang, et al., 1994). Several basic questions can be addressed regarding naturalized alien species in north Taiwan: (1) How many naturalized alien taxa exist in north Taiwan? (2) Which naturalized plant taxa is the most dominant in north Taiwan? (3) Where do those alien contributors come from? We test the following hypotheses: (1) North Taiwan, as tropical/subtropical in low altitude and temperate in high altitude with diversified terrains and climate, is vulnerable to plant invasions from all over the world; and (2) the majority of successful naturalized species were introduced from areas with climates similar to those prevailing in north Taiwan.. MATERIALS AND METHODS Study site We chose north Taiwan (24°18’N to 25°18’N latitude, 120°55’E to 122°00’E longitude) (Fig. 1) for this study. Taiwan, located on west Pacific Rim, has an area of 36,000 km2. Numerous hills and pinnacles ranging from 500 to 3,000 meter in elevation concentrate on the center and constitute about two thirds of the total area of the island. Straddling on the Tropics of Cancer, the major climate types are subtropical in the north and tropical in the south. Four counties of an area of 7,500 km2 in the north Taiwan experiencing subtropical climate were included, Taipei, Ilan, Tauyuan and Hsinchu, with an annual average temperature of 21.5 ° C and an annual average precipitation of 3,000 mm (Huang, et al., 1994). High cloud frequency result in relatively low radiation compared to that of tropical Taiwan in the south. Furthermore, northeast monsoon winds 7 .

(8) . usually carry moisture to this region in winter and make this region the wettest over the island. The altitude in this region ranges from 0 to 3,500 meter in elevation, and 70% of the study area is under 1,000 meter in elevation with plains and numerous hills (Huang, et al., 1994). The vegetation in this region mainly includes lowland rain forests, orchards, plantations, rice paddies, and crop field. Temperate forests can be found in the mountain areas (Huang, 1993; Huang, et al., 1994).. Materials To access the patterns of plant invasions, naturalized species were utilized to present potential invaders, since naturalization is the fundamental step for an introduced species to invade new territories (Pyšek et al. 2004). Wu et al. (submitted) and PBase (Taiwan plant database) was employed for naturalized species identification.. Methods Random sampling of one hundred plots (1% of the total grids) from a 1km2 Grid system in the north Taiwan by ArcGIS 9.0 (Fig. 1) (ESRI Inc., 1999-2004) was implemented in this study for plot selection. In each plot, the major habitat types were specified in advance by using orthophotos, including abandoned field, arable land, cemetery, riparian, etc. Field work was conducted in 2007 summer; and five to ten quadrats of 1 x 1 square meter in each habitat type were randomly selected. For each quadrat, species and relative coverage (%) of naturalized species were recorded. 8 .

(9) . Data analysis Statistics was performed to summarize basic numerical data, such as taxonomic data (numbers of family, genus, and species), life form (tree, shrub, climb, or herb), and origin level (endemic, native, naturalized, or cultivation). Additionally, taxonomic distributions of naturalized plants were summarized by families and genera. Biogeographic origins and their corresponding native climate were also summarized. Abundance was estimated by the total relative coverage (%) of each naturalized species, and relative frequency was calculated by the percentage of total plots divided by present plots. IVI (Importance value index) values of naturalized species were estimated by the sum of relative abundance and relative frequency. Species with the highest IVI value were considered as the dominant species. As for the origins, life forms and habit of most naturalized species, we referred to Wu et al. (submitted) and PBase.. RESULTS A total of 629 plant species belonging to 130 families and 409 genera, were recorded. Among these species, 52 endemic (8.3%), 416 native (66.1%), 146 naturalized (23.2%), and 15 cultural plants (2.4%) were recorded (Table 1-1 & Appendix). Among these species were 436 dicotyledons, 131 monocotyledons, 60 ferns, and two gymnosperms species. In life forms, there were 384 herbs, 95 climbs, 90 shrubs, and 60 trees. In origin data, there were 416 native plants, 146 naturalized plants, 52 endemic plants, and 15 cultivate plants. 9 .

(10) . Besides, the documented naturalized species represented 3% of the flora of Taiwan: 146 species in 111 genera and 38 families (Table 1-2). Among these species, 80% were dicotyledons and 20% were monocotyledons. No naturalized fern and gymnosperms species were found in north Taiwan. In addition, in life form, 71% were herbs, 15% were climbs, 12% were shrubs, and three species were trees. Asteraceae, Poaceae, and Fabaceae have many more naturalized species than any other families, and these three families constitute nearly half (47%) of the total naturalized flora of Taiwan (Fig. 1-2). The remaining families (e.g., Convolvulaceae, Euphorbiaceae, Amaranthaceae, Solanaceae, Araceae, Lamiaceae, Passifloraceae, Verbenaceae, etc) had < 10 naturalized species per family. The top three largest naturalized families, Asteraceae, Poaceae, and Fabaceae, had different expression between native and naturalized species in north Taiwan. For example, naturalized plants belonging to Asteraceae were almost 1.5 times of native ones; native plants belonging to Poaceae were almost 1.5 times of naturalized ones; and native plants belonging to Fabaceae were almost the same with naturalized. ones.. Some. families,. including. Convolvulaceae,. Amaranthaceae, Solanaceae, and Passifloraceae, had more naturalized species than native and endemic species. The remaining families, including Araceae, Lamiaceae, and Verbenaceae, had more native species than naturalized species. The family, Euphorbiaceae, had the same species number between native and naturalized species in north Taiwan. To deserve to be mentioned, the family, Passifloraceae, had only naturalized species investigated in north Taiwan. 10 .

(11) . The genus, Ipomoea (Convolvulaceae), has the most naturalized species (8), and the following genera, Alternanthera (Amaranthaceae), Amaranthus (Amaranthaceae), Phyllanthus (Euphorbiaceae), Passiflora (Passifloraceae), Solanum (Solanaceae), Paspalum (Poaceae), and Setaria (Poaceae), all have three species in their genera (Fig. 1-3). Besides, there were. seldom. native. and. endemic. species. belonging. to. the. above-mentioned genera with largest naturalized species. The species, Bidens pilosa L. var. radiata Sch. (Asteraceae), is the dominant species according to the IVI value (35.9), followed by Paspalum conjugatum Berg. (Poaceae; 4.5), Ageratum houstonianum Mill. (Asteraceae; 4.1), Ageratum conyzoides L. (Asteraceae ; 3.6), Ipomoea cairica (L.) Sweet (Convolvulaceae , 2.5), and Alternanthera philoxeroides (Moq.) Griseb. (Amaranthaceae; 2.0) (Fig. 1-4). The sum of the IVI value of the remaining 140 naturalized species was 41.5, and each of them was all less than 2.0. Most naturalized species were from the Americas, followed by Asia, Africa, Europe, and Eurasia (Fig. 1-5). Tropical areas of the Americas, Asia, and Africa were especially important sources. Europe and Eurasia represented important donors of temperate species naturalized in north Taiwan (Fig. 1-5).. DISCUSSIONS While naturalized species are in 38 families (Table 1-2), 47% of them belong to three families only: Asteraceae, Poaceae, and Fabaceae (Fig. 1-2 & Table 1-2). The large numbers of alien and native species 11 .

(12) . undoubtedly reflect the size of these families. It has been shown that global family size is correlated with the number of naturalized species in many families (Heywood, 1989). These three families have also been shown to be the major contributors of the alien floras in many regions of the world (Pysek, 1998). Besides these three families, the composition and importance of the major families of naturalized floras varied slightly in different regions. Convolvulaceae, Euphorbiaceae, Amaranthaceae, and Solanaceae are among the biggest contributors to alien floras in Asian countries like Taiwan and Korea (Wu, et al., 2004b; Zerbe et al., 2004), but they are relatively less important in some European countries (Weber, 1997; Vilá & Muñoz, 1999; Pysek et al., 2002). Different climates and biogeographical relations may matter. Solanaceae, Convolvulaceae, and Amaranthaceae are considered as tropical or warm-climate families, and many of their species may not be adapted to climates such as those of northern and central Europe. The genera with most naturalized species are, not surprisingly, among the largest genera in the world (Fig 1-3). Ipomoea, Alternanthera, Phyllanthus, Passiflora, Solanum, Paspalum, and Setaria all have hundreds of species, although Amaranthus has an intermediate size of 60 species (Mabberley, 1997). Overrepresentation of Ipomoea is an obvious reason of why the ratio of naturalized species to the global species number is so high in their respective family, Convolvulaceae. (Wu, et al., 2004b). The reason that this genus is remarkably successful in Taiwan deserves investigation. 12 .

(13) . The species, Bidens pilosa L. var. radiata Sch. (Asteraceae), with the highest IVI value (35.9, almost 18% of the total flora) in north Taiwan may be contributed from its diversely invasible physiological and biotic traits, such as high germination everywhere, well-growth in varied environments, showy flower, and barbed achene (Wu, 2005; Hsu, 2006; Huang, 2008). Germination everywhere and well-growth in varied environments supply better abilities in establishment; showy flower makes it more visible for pollinators; and barbed achene favors seed dispersion crossing animal’s fur or human trouser legs. To summarize, well-adaptation of B. pilosa var. radiata in every invasive stage, including establishment, reproduction, and dispersion, makes it a large amount of population in north Taiwan. The fact that a remarkable proportion of naturalized species originated from tropical and temperate regions (Fig. 1-5) confirms the assumptions that species might adapt well to a new environment with a climate similar to their ‘homeland’ (Corlett, 1988; Corlett, 1992). North Taiwan has a diversity of habitats ranging from tropical in low altitude to alpine in high altitude, and this may contribute to accommodation of species from regions with a variety of climates. However, we do not have an explanation why American species are so copiously represented and why many of these American species have been on the island for decades (Wu et al., 2004a). Unfortunately, no of what has been found in the historical events in last hundred years (Wu et al., 2004b). On the contrary, it seems reasonable to expect that more species were introduced from European or Asian regions, because many of them were very likely 13 .

(14) . brought into Taiwan by the Dutch or Spanish from Europe on their way to China during the 17th and 18th centuries (Wu et al., 2004b). Very likely, these traders also brought some species from Africa, tropical America and southern Asia to Taiwan on their way to the East (Merrill, 1912). North Taiwan, an epitome of Taiwan Island like Hawaii, accommodates many climate zones and terrains, from alpine to tropical and coastal, but the intensity of plant invasions appears to be substantially lower than that in Hawaii. The percentage of naturalized species to total number of local species alone even suggests that Taiwan is much more resistant to establishment of alien species (Wu, et al., 2004b). Furthermore, the number of species per log (area) of Taiwan is closer to those of continents (Vitousek et al., 1997), again suggesting that Taiwan is more resistant to plant invasions than other island regions. Proximity to the largest continent may be part of the story. However, more biogeographical and ecological studies in south-east Asia are needed before we reach a more complete understanding of invasion patterns and processes in this area.. 14 .

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(27) . Figure 1-1. Spatial distribution of our sampling sites around north Taiwan. 27 .

(28) . Table 1-1. Numerical summary of flora in north Taiwan by taxonomic levels, life forms, and origin Ang.. Origin. Life form. Taxonomic. Total Pte.. Gym.. Dic.. Mon.. Family. 22. 2. 89. 17. 130. Genus. 36. 2. 287. 84. 409. Species. 60. 2. 436. 131. 629. Tree. 2. 2. 55. 1. 60. Shrub. 0. 0. 83. 7. 90. Climb. 0. 0. 81. 14. 95. Herb. 58. 0. 217. 109. 384. Endemic. 1. 1. 40. 10. 52. Native. 59. 1. 270. 86. 416. Naturalized. 0. 0. 117. 29. 146. Cultivation. 0. 0. 9. 6. 15. Note: Those abbreviations stand for: Pte., Pteridophytes; Gym., Gymnosperms; Ang., Angiosperms; Dic., Dicotyledons; and Mon., Monocotyledons. The numbers in the columns of life form and origin stand for species number.. 28 .

(29) . Table 1-2. Numerical summary of naturalized flora in north Taiwan by taxonomic levels, life forms, and origin Ang.. Life form. Taxonomic. Total Pte.. Gym.. Dic.. Mon.. Family. 0. 0. 32. 6. 38. Genus. 0. 0. 89. 22. 111. Species. 0. 0. 117. 29. 146. Tree. 0. 0. 3. 0. 3. Shrub. 0. 0. 17. 1. 18. Climb. 0. 0. 21. 1. 22. Herb. 0. 0. 76. 27. 103. Note: Those abbreviations stand for: Pte., Pteridophytes; Gym., Gymnosperms; Ang., Angiosperms; Dic., Dicotyledons; and Mon., Monocotyledons. The numbers in the column of life form stand for species number.. 29 .

(30) . 40. Species number. 35 Native. 30. Naturalized. 25. Endemic. 20 15 10 5 0. Figure 1-2. Major families according to their number of naturalized species in north Taiwan 9 8 Native. Species number. 7. Naturalized. 6 5 4 3 2 1 0. Figure 1-3. Major genus according to their number of naturalized species in north Taiwan. 30 .

(31) . 40 35 30. IVI. 25 20 15 10 5 0 Bidpil Pascon Agehou Agecon Ipocai. Altphi Puelob Setpal Consum Pasdil. Figure 1-4. The top ten naturalized species in north Taiwan according to IVI value Note: Those abbreviations stand for: Bidpil, Bidens pilosa L. var. radiata Sch.; Pascon, Paspalum conjugatum Berg.; Agehou, Ageratum houstonianum Mill.; Agecon, Ageratum conyzoides L. ; Ipocai, Ipomoea cairica (L.) Sweet; Altphi, Alternanthera philoxeroides (Moq.) Griseb.; Puelob, Pueraria lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi; Setpal, Setaria palmifolia (J. König) Stapf; Consum, Conyza sumatrensis (Retz.) Walker; and Pasdil, Paspalum dilatatum Poir. 100 90. Mediterranean. Species number. 80. Temperate. 70. Tropical. 60 50 40 30 20 10 0 America. Asia. Africa. Europe. Eurasia Australia Oceania. Unclear. Figure 1-5. Native areas and climates of naturalized species in north Taiwan. 31 .

(32) . Chapter 2. The Impacts of Naturalized Legumes on Plant Communities in north Taiwan. 摘要過去研究顯示，入侵植物常對於當地的生物多樣性造成衝擊，包括競爭排除、竭盡水源或改變微棲地物化性質等。其中，改變微棲地物化性質往往造成深遠且不可逆的影響；然而，此環節卻鮮少被討論。在眾多改變微棲地物化性質的機制中，固氮作用是最常見且能改變土壤物化性質的重要機制之一。一般而言，豆科(Fabaceae)植物能藉由固氮作用適應當地環境並增加該地區土壤的生物承載量，進而改變該地區植物之生物量及多樣性。本研究設立下列四個假說以探討歸化之豆科植物在北臺灣植物群落之生物量及多樣性所造成之衝擊性：(1) 歸化豆科植物的存在與相對較高的植物生物量及多樣性有關；(2) 歸化豆科植物提昇了土壤含氮量；(3) 歸化豆科植物同時增加原生及外來植物之生物量及多樣性；(4) 歸化豆科植物在不同棲地類型之植物群落造成之衝擊性會有所不同。實驗以北臺灣為樣區，利用每平方公里之網格系統，隨機選取 100 個 1km2 樣區，利用正射化影像(Othophoto)判定棲地類型，並各 32 .

(33) . 自選取五到十個不等的 1m2 小樣方，記錄 GPS、海拔高度、棲地類型、植物種類以及覆蓋度等，並轉換成多樣性指數包括 Shannon(H’)、 Simpson(λ)、Pielou 均勻度指數(J)、Berger-Parker 優勢度指數(BP)、物種數(S)及總覆蓋度(C)等六項指數；另外，收集土壤樣本以評估歸化豆科植物之存在與否造成含氮量之差異性。結果顯示，在 100 km2 中 2242m2 的小樣方共記錄了 16 種歸化豆科植物，其中以大葛藤 (Pueraria lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi)為最優勢之種類；大多數的歸化豆科植物為原產於熱帶地區的草本，且偏好特定的棲地類型，如農地、河岸地、荒廢地及路邊。在土壤營養鹽部份，歸化豆科植物提高了局部的氮總量；另外，存在歸化豆科植物會顯著增加外來歸化植物之生物量及多樣性，但對於原生植物卻沒有增加或減少的趨勢。然而，若將歸化豆科植物從分析中移除，其存在與否對於其它外來歸化植物並沒有增加或減少的趨勢。此外，分別探討歸化豆科植物種數最多的五種棲地，包括荒廢地、河岸、農地、墓地及路邊，其受衝擊程度與整體完全一致，即存在歸化豆科植物會顯著增加這五種棲地類型之外來歸化植物生物量及多樣性，但對於原生植物依舊沒有增加或減少的趨勢；但若將歸化豆科植物從分析中移除，其存在與否亦對於這五種棲地類型之其它外來歸 33 .

(34) . 化植物並沒有增加或減少的趨勢。根據我們的結果，北臺灣地區之歸化豆科植物對於當地植物群落生物量與多樣性之衝擊幾乎接近中性；然而，我們仍需密切注意歸化豆科植物在臺灣中部與南部這些亞熱帶區域所造成之衝擊，一方面比較改變棲地物化因子之相同分類群在不同緯度間之衝擊性必定是個有趣的議題；另一方面，對於這些能改變棲地性質之分類群的了解能更佳透徹。. 關鍵字：入侵植物、歸化植物、衝擊、改變棲地者、豆科、固氮作用、生物承載量、生物量、生物多樣性. 34 .

(35) . ABSTRACT It has been shown that invasive plants usually impact local biodiversity by competitive exclusion, water depletion, microhabitat transformation, etc. Among these impacts, nitrogen-fixation is one of the most serious transform mechanisms invasive plant, such as legumes, may employ. Although the impacts of invasive habitat transformer have been discussed in few studies, comprehensive approaches on the impacts of local biodiversity and biomass upon community level have yet been conducted. My main purpose of this study was to estimate the impacts of naturalized legumes, notorious habitat transformers, on local biomass and biodiversity. To generate better understanding of the impacts caused by naturalized legumes on local plant communities, we developed and tested the following hypotheses: (1) Presence of naturalized legumes is associated with relatively higher biomass and biodiversity; (2) Presence of naturalized legumes elevates soil nitrogen; (3) Naturalized legumes increase local biomass and biodiversity of both native and naturalized species; (4) The impacts of naturalized legumes on local communities are varied along habitat types. Furthermore, we also anticipated answering the following questions: (1) What are the dominant naturalized legumes in the study areas? ; (2) What are the favorite habitat types of naturalized legumes? The field investigation was carried out in four counties in north Taiwan. By using 1km2 grid systems, one hundred of total grids were randomly selected as the sample areas. Five to ten square meters 35 .

(36) . quadrates; furthermore, were investigated. A total of 2,242 1-km2 quadrats and twelve habitat types were recorded. Plant species and coverage of all native and naturalized species were collected, and IVI values were calculated for each naturalized legumes for the summary of dominance. Six biodiversity indices, including Shannon-Weaver (H’), Simpson (λ), Pielou evenness (J), Berger-Parker Dominance (BP) indices and species numbers (S), and total coverage (C) were summarized for further comparisons. In addition, soil samples were collected in pairs, presence and absence of naturalized legumes, to estimate the differences of available nitrogen. A total of 629 species belonging to 130 families and 409 genus were documented. Among these species, 16 are naturalized legumes. Pueraria lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi was the dominant species according to the IVI value, were recorded. Most of the naturalized legumes were herbs, from tropical areas, and preferred specific habitats, such as arable land, riparian, abandoned field, and roadside. In the part of soil nutrient, total nitrogen content was increased locally by naturalized legumes. Besides, local biomass and biodiversity of naturalized flora were increased significantly by naturalized legumes, but neither did native flora. However, the biomass and biodiversity of naturalized flora, excluding naturalized legumes, were not elevated on the enriched soils, either. Furthermore, separately for the habitat types, the results were consistently with overall condition that naturalized legumes significantly increased local biomass and biodiversity in those legume-preferred habitat types. But when naturalized legumes were 36 .

(37) . excluded, there were no significant difference in separate habitats, either. According to our results, the impacts of naturalized legumes on local communities, including biomass and biodiversity, in north Taiwan were nearly neutral. However, we should still pay attention to naturalized legumes whose impacts on central and south Taiwan. On the one hand, comparisons of impacts of the same taxon of habitat transformers among different latitudes would be an interested issue; on the other hand, the comprehensive study for habitat transformers would be further clarified.. Key word: Invasive plant, Natulized plant, Impact, Habitat transformer, Fabaceae, Nitrogen fixation, Carry capacity, Biomass, Biodiversity. 37 .

(38) . INTRODUCTION The impacts of plant invasions on local plant communities have been documented worldwide, including biodiversity reduction, composition alternation,. competitive. exclusion,. resource. depletion,. habitat. transformation, etc (Vitousek & Walker, 1989; Vitousek, 1990; Richardson et al., 2000b; Yoshida & Oka, 2004; Owens & Moore, 2007). Among these impacts, habitat transformation has relatively profound effects, since abiotic and biotic components and interactions of local community may be modified consequently (Marr, 1993; Vitousek, 1994). The commonest habitat transformation is usually performed by alien plant transformers, such as Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae,. Elaeagnaceae,. Fabaceae,. Myricaceae,. Rhamnaceae,. Rosaceae, and Ulmaceae, through nitrogen-fixation (de Faria, et al., 1989; Vitousek, 1990; Soltis, et al., 1995; Maron & Connors, 1996), and it often facilitates further invasions by naturalized species (Vitousek & Walker, 1989; Vitousek, 1990; Maron & Connors, 1996). The transformation of habitats starts with enriched soil following symbiosis of inhabited legumes and nitrogen-fixing bacteria and the process is irreversible (Paker & Paker, 2006). Consequently elevated local biomass and biodiversity following habitat transformation have been shown in many regions over the world (Vitousek & Walker, 1989; Vitousek, 1990; Maron & Connors, 1996; Richardson et al., 2000a; Zahran, 2001; Haubensak & Parker, 2004). Although elevated soil nitrogen may provide equal opportunities for both of native and naturalized species, introduced weeds are usually the beneficiaries of raising carry capacity due to their high 38 .

(39) . nutrient exploitation capacity (Huenneke, et al., 1990; Vitousek, 1990; Marr, 1993; Vitousek, 1994; Maron & Connors, 1996). However, the effects of transformation to local plant community, including native and naturalized, were seldom discussed. Fabaceae, the major plant group performing symbiosis with nitrogen fixing bacteria, is one of the most important plant families over the world and one of the largest contributors to the naturalized floras (Corlett, 1988; Corlett, 1992; Pyšek, 1998; Pyšek et al., 2002; Wu et al., 2004a&b; Wu, unpublished) as well. It has been shown that about 84 % of Fabaceae performs. symbiosis. with. nitrogen. fixing. bacteria,. especially. Papilionoideae (97%; de Faria, et al., 1989). Although reports on symbiosis of alien legumes and native nitrogen fixing bacteria are usually unavailable (Schlaepfer, et al., 2005; Reinhart & Callaway, 2006), root nodules of naturalized legumes are frequently seen in the fields according to our experiences. The capacity of conducting symbiosis with nitrogen-fixing bacteria, the alien legumes usually naturalized in specific habitats, such as riverbank, roadside, etc (Wu, et al., 2005). These habitats equipped with high-frequency disturbance often facilitate dormancy breaking process via damaging the thick seed coats. It has been shown that nitrogen fixing bacteria usually effectuate nitrogen fixing mechanisms in habitats where soil nitrogen is relatively not available. The influences of naturalized legumes in different habitats, therefore, may be different in terms of increasing local biomass and biodiversity (Corlett, 1988; Corlett, 1992; Williamson & Fitter, 1996; Zalba et al., 2000; Alston & Richardson, 39 .

(40) . 2006; Morales & Aizen, 2006; Wu, 2006; Wu et al., submitted). For example, in poor-nutrient habitats, such as abandoned field, riparian, and roadside, are expectably more beneficial to naturalized legumes. In addition, there are also frequently high disturbance in the foregoing habitats, indigenous preference of high-disturbed habitats and possibly nutrient elevation via naturalized legumes are simultaneously contributed to exotic plant and accompany to serious invasion (Richardson, 2000a; Alston & Richardson, 2006). To generate better understanding of the impacts caused by naturalized legumes on local plant communities, we developed and tested the following hypotheses: (1) Presence of naturalized legumes is associated with relatively higher biomass and biodiversity; (2) Naturalized legumes increase local biomass and biodiversity of both native and naturalized species; (3) The impacts of naturalized legumes on local communities varied along habitat types (4) Presence of naturalized legumes elevates soil nitrogen content. Furthermore, we also anticipated answering the following questions: (1) What are the dominant naturalized legumes in the study areas? ; (2) What are the favorite habitat types of naturalized legumes?. MATERIALS AND METHODS Study site In this study, we employed the north Taiwan (24°18’N to 25°18’N, 120°55’E to 122°00’E) as the study site. Taiwan, located on west Pacific Rim, has an area of 36,000 km2. Numerous hills and pinnacles ranging 40 .

(41) . from 500 to 3,000 meters in elevation were concentrated in the center and constitute about two thirds of the total area of the island (Huang, et al., 1994). Straddling on the Tropics of Cancer, the major climate types are subtropical in the north and tropical in the south. Four counties of an area of 7,500 km2 in the north Taiwan experiencing subtropical climate were included, Taipei, Ilan, Tauyuan and Hsinchu, with an annual average temperature of 21.5°C and an annual average precipitation of 3,000 mm (Center Weather Bureau data, 1971 to 2000). High cloud frequency result in relatively low radiation compared to that of tropical Taiwan in the south. Furthermore, northeast monsoon winds usually carry moisture to this region in winter and make this region the wettest over the island. The altitude in this region ranges from 0 to 3,500 meter in elevation, and 70% of the study area is under 1,000 meter in elevation with plains and numerous hills (Huang, et al., 1994). The vegetation in this region mainly includes lowland rain forests, orchards, plantations, rice paddies, and crop field. Temperate forests can be found in the mountain areas (Huang, 1993; Huang, et al., 1994).. Materials Fabaceae, also called legumes, contained three subfamilies (Mimosoideae, Caesalpinioideae, and Papilionoideae), about 650 genera, and over 18,000 species over the world (Huang, et al., 1993). In Taiwan, about 60 genera and 170 species were contained to Fabaceae (Huang, et al., 1993). Besides, there were about 43 genera and 81 naturalized legumes belonging to Fabaceae in Taiwan (Wu, 2004a; Wu, et al., 41 .

(42) . submitted). Previous studies about naturalized legumes in Taiwan included their background data and minimum residence time (Wu, et al., 2003), correlation between biotic characteristic and their invasiveness (Wu, et al., 2005), and correlation between local environmental factors and their distribution (Lee, 2003). According to those previous studies, naturalized legumes could be used as a good model taxon to comprehend the impacts of habitat transformers on biodiversity in the field.. Field investigation Field data A total of 100 plots whose size were one square kilometer were randomly sampled in advance by applying a 1km2 Grid system on the north Taiwan by ArcGIS 9.0 (see Fig. 1-1)(ESRI Inc., 1999-2004) In each plot, major habitat types were specified in advance by using orthophotos, including abandoned field, acacia woody forest, arable land, bank, betel nut, cemetery, forest, orchard, riparian, roadside, trait in grass and trait in wood. Five to ten 1-m2 quadrats of each habitat type were randomly sampled. Species, both of native and naturalized, and the coverage of each species were recorded. Field work was conducted in 2007 summer during the flowering season of legume species for accurate identification.. Soil collection Soil samples were collected in pairs, presence and absence of naturalized legumes, to estimate the differences of available nitrogen. Since naturalized legumes were not found in all land use types, we only 42 .

(43) . employed the habitat types where naturalized legume inhabited. In each habitat type, two quadrats with and without naturalized legumes were selected. In each quadrat, five soil samples of 15 to 20 cm depth at the center and four corners were collected. The soil samples were air-dried for five to seven days, and then, filtered by sieve plate with 20 meshes afterwards for further analyses.. Data analysis Field data Importance value index (IVI values), the sum of relative abundance and relative frequency, were calculated for each naturalized legumes for the summary of dominance. Five biodiversity indices and total coverage were summarized for further comparisons, including Shannon-Weaver (H’), Simpson (λ), Pielou evenness (J), Berger-Parker Dominance (BP) indices and species numbers (S) by SDR4.0 (Pisces Conservation Ltd, 2007). The field data were categorized into two groups firstly, habitats completely have no naturalized legumes (CHN) and habitats harbored naturalized legumes. The later was further separated into two categories, quadrats with legumes (QWt) and quadrats without naturalized legumes (QWo). One factor ANOVA was performed to examine differences of coverage and biodiversity among these three treatments, CHN, QWt, and QWo in overall situation and five major habitat types existing naturalized legumes. All tests were performed using JMP6.0 statistical software (Statistical Discovery TM From SAS, 2005).. 43 .

(44) . Soil data For total nitrogen, we followed Bremner (1965). Pair-t test was performed to examine differences between naturalized legumes presented or not by JMP6.0. Ten paired soil samples, with presence and absence of naturalized legumes, were collected in the habitat types where naturalized legume inhabited. Our soil data were firstly transformed to Log of each milligram of total nitrogen content per ten gram of soil to match normal distribution and one pair were excluding as an outlier.. RESULTS Field data Among the naturalized species, 16 legumes (10.96% of the total naturalized flora) in north Taiwan were observed in the field (Table 2-1). The major compositions of life form of the 16 naturalized legumes were herb and shrub; the major origins were America and Asia; and the major climate region of their origin geographic distribution was tropical. According to the IVI value, the most dominant species was Pueraria lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi (1.874), followed by Calopogonium musunoides Desv. (0.616), Mimosa pudica L. (0.422), Leucaena leucocephala (Lam.) de Wit. (0.392), and Sesbania sesban (L.) Merr (0.255). Among the twelve habitats, the top three habitat types with the total proportion of native species were trail in grass (95%; 38/40), forest (92.2%; 141/153), and trail in wood (89.8%; 167/186); and that of naturalized species were in cemetery (46.8%; 65/139), orchard (41.4%; 44 .

(45) . 24/58), and abandoned field (39.8%; 82/206) (Table 2-2). Moreover, only nine habitat types accommodated naturalized legumes. Abandoned field and riparian are the most important habits for naturalized legumes according to species number and IVI value respectively, followed by arable land, cemetery, and roadside. Significant differences of biomass and biodiversity were found among three groups (Table 2-3). Firstly, for whole flora, total biodiversity and biomass in quadrats with naturalized legumes (QWt treatment) were significantly higher than other two groups, CHN and QWo; however, Berger-Parker Dominance index of QWt quadrats was significantly lower than those of CHN and QWo groups in overall and top five habitat types besides cemetery (Table 2-3a & Table 2-4a). Secondly, for native flora, total biodiversity and biomass in quadrats entirely without naturalized legumes (CHN treatment) were significantly higher than QWo quadrats; however, Berger-Parker Dominance index of CHN quadrats was significantly lower than those of QWo group in overall and arable land. Besides, biomass of QWt treatment in riparian and abandoned fields was significantly lower than the other two groups, QWo and CHN. On the other hand, there were no significant differences in the remaining index between QWt treatment and the other two groups in all habitats (Table 2-3a & Table 2-4b). Finally, for naturalized flora, the tendency was the same with whole flora that total biodiversity and biomass in quadrats with naturalized legumes (QWt treatment) were significantly higher than other two groups, CHN and QWo; however, Berger-Parker Dominance index of QWt quadrats is significantly lower than those of CHN and QWo groups in 45 .

(46) . overall and top five habitat types besides cemetery (Table 2-3a & Table 2-4c). When naturalized legumes were deducted from QWt treatment (QWt –NL, Table 2-3b & Table 2-5), the tendencies in whole and naturalized flora were different from Table 2-3a & Table 2-4. Biomass of QWt treatment became significantly lower than those CHN and QWo groups in overall and abandoned field of whole and naturalized flora, arable land and riparian of whole flora. Besides, there were no significant differences in the remaining indices between QWt after naturalized legumes were deducted and those two groups, QWo and CHN.. Soil data No significant differences of average soil nitrogen are shown between the quadrats with and without naturalized legumes. However, the soil nitrogen of samples collected in the centers of the quadrats with and without naturalized legumes is marginally significantly different (Table 2-6). On the other hand, nearly significantly difference of the soils collected in the center and in the corners is represented (Table 2-7). DISSCUSSIONS According to our results (Table 2-3a), the first hypothesis that presence of naturalized legumes is associated with relatively higher biomass and biodiversity is supported. This difference, as we anticipate, can be a result of elevating soil nutrients in terms of soil nitrogen (Table 2-6). Symbiosis of naturalized legumes and nitrogen fixing bacteria 46 .

(47) . enriches soil nitrogen as well as local carrying capacity; therefore, additional biomass can be supported (Aronson, et al., 1992; Pan, et al., 1993; Maron, et al., 1996; Parveen, et al., 1996). Complicated mechanisms, inter-specific and intra-specific interactions may be involved in elevating local biodiversity as we have seen in our study (Throop, 2005; Saidi, et al., 2007). However, the beneficiaries, in terms of native or naturalized species, of the enriched soil nutrients require further studies. The second hypothesis is partially supported, since the biomass and biodiversity of native flora did not increase in the quadrats with naturalized legumes. The biomass and biodiversity of naturalized flora, excluding naturalized legumes, are not elevated on the enriched soils, either. Additional biomass and biodiversity of total flora are; therefore, most from naturalized legumes alone (Table 2-3) (Vitousek, 1990; Maron & Connors, 1996). Dominant naturalized legumes with top IVI value in our case are either shrubs or lianas, and their advantages of exploiting available resources and nutrients have been confirmed (Aronson, et al., 1992); however, competition exclusion of native and naturalized species does not occur. Although enriched soil may provide additional niche and equal opportunities for native and naturalized species to arrive and establish (Herben, et al. 2004), the advantages of being exposed to available resources at the first minute may facilitate the inhabited naturalized legumes to fill the niche immediately (Tilman 2004; Kreyling, et al., 2008). The impacts of naturalized legumes on local communities are varied 47 .

(48) . along habitat types, and this result supports our third hypothesis. In legume-preferred habitats, e.g. arable land, riparian, abandoned field, and roadside, legumes do not suppress the biomass and biodiversity of other naturalized species (Table 2-4 & Table 2-5). Base on the previous studies, the leguminous seeds were always with thick and impermeable coats, and made them with dormancy (Rolston, 1978). To break the dormancy, daily alternating temperature and mechanical damage was most commonly used in natural habitat (Souza & Marcos-Filho, 2001; Baskin, 2003; Van Assche, et al., 2003). High frequency and large-scale disturbance such like cultivator working in arable land, water erosion in riparian and weeding behavior in roadside, would all supply a force for leguminous seed coat easily being broken (Paynter, et al., 2003; Spooner, 2005). Once the seed coat was broken, leguminous cotyledons could rapidly absorb water and expand, and then germinate for later individual establishment. The advantages of well expressions in their favorite habitats may facilitate rapid exploitation of additional nitrogen and fill the niche (Jonathan, et al., 2008; Tilman 2004; Kreyling, et al., 2008); however, the impacts of local communities by naturalized legumes through symbiosis with nitrogen-fixing bacteria were not evident. Perhaps, soil nitrogen is not a limiting factor in these habitats and species do not experience intensive competition of available resources. Another explanation might be unfulfilled carrying capacity. Niches are always available in these habitats; therefore, competition exclusion did not exist. Cemetery showed another special pattern of co-existence of naturalized legumes and other species. It seems to provide equal 48 .

(49) . opportunities for native and naturalized species, since no significant difference of native and naturalized flora was found among the treatments, CHN, QWo, and QWt (Table 2-4 & Table 2-5). Chinese worship culture implemented in this kind of habitat seems to create empty niches frequently. Periodical weeding and burning behaviors were cyclically occurred, and this may accelerate nutrients returning to the earth (Døckersmith, et al., 1999). Relatively higher average soil nitrogen content (2.38mg/g soil) then others habitats (0.45 in roadside to 1.14 in arable land) and resulted in relatively larger biomass of naturalized flora in cemetery (74.7% ± 30.7%) than others habitats (45.2% in riparian to 56.6% in roadside, data not shown). Even though naturalized legumes were dominant in cemetery according to the IVI value, the effect of biomass and biodiversity might be diluted by amounts of others naturalized flora. The ratio of naturalized legumes to total naturalized flora in north Taiwan was much lower than in whole Taiwan Island (13.34%; Wu, et al., submitted), China (15.13%; Wu, et al., submitted), Singapore (21.32%; Corlett, 1988), and India (16.76%; Reddy, 2008). Comparing with temperate countries, the ratio of naturalized legumes was much higher than Czech (5.59%; Pyšek, et al., 2002). Besides, we could see that most of the 16 naturalized legumes in our field investigation were from tropical or subtropical areas (Table 2-1). It seemed to show that naturalized legumes in Taiwan preferred to the tropical habitat in south Taiwan (Mabberley, 1997). The presence of naturalized legumes elevates soil nitrogen, and this 49 .

(50) . result supports our fourth hypothesis (Table 2-6). However, the increased soil nitrogen caused by naturalized legumes did not impact local biomass and biodiversity as our expected (Table 2-3). According to Table 2-1 &2-7, total soil nitrogen was only increased restricted and localized in the standing site of each individual, and produced nitrogen by naturalized legumes cannot diffuse and transport to distance even within a meter. The transformation function of naturalized legumes seems to be amplified, and did not exist in our case, and the distribution pattern of naturalized legumes may be the key point. Naturalized legumes usually distribute individually in the field without forming monoculture and large coverage in north Taiwan; therefore, synthesized nitrogen by root nodules may simply accumulate on site and utilized by naturalized legumes alone. Although neighbors of native and naturalized plant are very close to the naturalized legumes, stationary soil nitrogen cannot be shared. In consideration of the total IVI of naturalized legumes, the impacts of soil nutrient caused by naturalized legumes, the “transformers”, do not seem to be serious in the north Taiwan.. 50 .

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