Journal of Biogeography, 30, 1329–1337 Phytogeography of Hong Kong bryophytes Li Zhang1,2* and Richard T. Corlett1 1Department of Ecology & Biodiversity, The University of Hong Kong, Hong Kong, China and 2South China Institute of Botany, The Chinese Academy of Sciences, Guangzhou, China Abstract Aim Hong Kong is in a biogeographically interesting location on the northern margins of the Asian tropics. This paper analyzes the phytogeography of Hong Kong’s bryophyte flora for the first time. Location Hong Kong lies on the South China coast, 22
9¢–22
37¢ N, 113
52¢–114
30¢ E. It is one of the most densely populated places in the world, but because of the rugged topography only 20% of the total land area of 1100 km2 is urbanized. Although 130 km south of the Tropic of Cancer, it has a subtropical climate with distinct hot, humid and cool, dry seasons. Methods The analysis is based on a new and relatively complete inventory of Hong Kong’s bryoflora. Each taxon was assigned to a phytogeographical pattern on the basis of its present worldwide distribution. Krober’s percentage similarity was employed to evaluate the floristic affinities between different regions. Results The bryophyte flora consists of at least 360 species and twelve infraspecific taxa in 159 genera and seventy families, of which four taxa are locally endemic. The largest families are Lejeuneaceae (fifty-one taxa), Fissidentaceae (28), Hypnaceae (21), Dicranaceae (20), Calymperaceae (18), and Sematophyllaceae (15). The largest genera are Fissidens (28), Cololejeunea (17), Lejeunea (10), Syrrhopodon (9), Frullania (8), and Macromitrium (8). Fourteen phytogeographical patterns are recognized. The East Asian pattern is the commonest (seventy-three taxa, 19.6%), followed by Asian–Australian– Oceanian (45, 12.1%) and Temperate (44, 11.8%). Overall, a third of taxa have tropical distributions. The bryofloras of eleven regions were compared with that of Hong Kong. The most similar regions are Hainan Province, Taiwan Province, and Japan. Mosses and liverworts show very similar phytogeographical distributions. Main conclusions (1) The Hong Kong bryoflora is best described as northern marginal tropical, with a strong Eastern Asian and Temperate influence; (2) the region of closest phytogeographical affinity for which information is available is Hainan; (3) in comparison with vascular plants, vertebrates and those invertebrate groups for which there is information, the bryoflora has a relatively low proportion of tropical taxa; (4) the bryoflora of Hong Kong appears to be exceptionally rich for its small area. Keywords Bryophytes, China, floristics, liverworts, mosses, phytogeography. INTRODUCTION The South China region is ideal for studying the climatic limits of species distributions because it is part of an uninterrupted belt of forest climates that extends from the *Correspondence: Li Zhang, South China Institute of Botany, The Chinese Academy of Sciences, Guangzhou 510650, China. E-mail: zhangli@graduate.hku.hk  2003 Blackwell Publishing Ltd equator to the latitudinal limit of forest growth in Siberia, without the intervening arid zone that limits contact between tropical and extra-tropical forest floras elsewhere. Hong Kong is in an interesting phytogeographical position within this belt. It is 130 km south of the Tropic of Cancer but, like most of tropical South China, is subject to periodic influxes of cold air from the north in winter. These cause rapid drops in temperature, with occasional frosts down to sea-level (Dudgeon & Corlett, 1994). If, as is often assumed, tropical 1330 L. Zhang and R. T. Corlett floras and vegetation extend to the 0
C isoline for absolute minimum temperature (e.g. Prentice et al., 1992), Hong Kong lies right on the northern edge of the tropics. Moreover, Takhtajan (1986) places the boundary between the Holarctic and Palaeotropical floral kingdoms for angiosperms a few kilometres to the west. Floristic studies must be based on a firm foundation of careful taxonomic studies (Deguchi & Iwatsuki, 1984). While the vascular plant flora of Hong Kong has been well studied for over a century, a relatively complete inventory of the bryoflora has only recently been compiled (Zhang, 2003). This inventory is the result of detailed and systematic field surveys over 3 years, examination of historical specimens, and critical reviews of relevant publications. It is therefore possible for the first time to carry out a phytogeographical analysis of Hong Kong bryophytes. The present geographical distributions of plants are the result of climate, habitat availability and dispersal history (Preston & Hill, 1997). Schuster (1983) emphasized that phytogeographic analysis of bryophytes is considerably more interesting than might be supposed. He suggested that Ô… bryophytes, … potentially offer a better clue to the solution of phytogeographical problems than do many vascular plantsÕ by reason of their abilities to survive in a small microenvironment, long after the general climate of the region has become very definitely inimical. In the case of Hong Kong, where all vascular plant communities have been drastically modified by centuries of human impacts and only fragments of forest survive, bryophytes may offer the best opportunity to look at the geography of more or less natural plant communities. The purposes of the paper are to analyse the phytogeographical patterns of Hong Kong bryophytes, to identify the phytogeographical nature of the bryophyte flora, and to elucidate the affinities with different regions. STUDY AREA Hong Kong (22
9¢–22
37¢ N, 113
52¢–114
30¢ E) lies on the south China coast, with a total land area of 1100 km2. Hong Kong has a population of almost 7 million people, but only 20% of the land area is urbanized because steep hills occupy most of the remainder (Dudgeon & Corlett, 1994). The highest peak, Tai Mo Shan, reaches 957 m. Most of Hong Kong is underlain by igneous rocks of Jurassic age. The climate is subtropical, with distinct hot, humid and dry, cool seasons. Mean annual rainfall ranges from 1300 mm at Waglan Island in the southeast of Hong Kong waters to more than 3000 mm near the summit of Tai Mo Shan, with about 80% falling between May and September. Mean annual temperature ranges from 22.8
C in lowland Kowloon to 18.3
C near the summit of Tai Mo Shan. Subzero temperatures and frost occur annually at the highest altitudes and less frequently down to around 400–450 m on Tai Mo Shan, and down to sea level in the northern New Territories. Deforestation of coastal South China started at least 1000 years ago and the original forest cover of Hong Kong had largely disappeared by the nineteenth century, except for some tiny, disturbed patches in inaccessible sites at high altitude. Today, most non-urban areas are occupied by grassland, shrubland, secondary forest or exotic plantations (Zhuang & Corlett, 1997). Bryophyte diversity is now concentrated in forest patches, particularly along streams. METHODS This paper is based on the bryophyte list of Zhang (2003). Each taxon was assigned to a phytogeographical pattern on the basis of its present-day global distribution as determined from all available sources of information. The bryophyte flora of Hong Kong was compared with the bryofloras of other regions with reliable floras or checklists using Krober’s percentage similarity. The main advantage of this formula is that it minimizes the effect of the size difference between the two regions under comparison (Tan, 1984). Krober’s percentage similarity ¼ 50C(A þ B)/AB, where A is the number of taxa occurring in the first region; B, the number of taxa occurring in the second region; C, the number of taxa shared by both regions. RESULTS The bryoflora of Hong Kong The known bryophyte flora of Hong Kong consists of 360 species and twelve infraspecific taxa in seventy families and 159 genera, of which 238 taxa are mosses, and 134 taxa are liverworts and hornworts (Zhang, 2003). The largest families are Lejeuneaceae (fifty-one taxa), Fissidentaceae (28), Hypnaceae (21), Dicranaceae (20), Calymperaceae (18), and Sematophyllaceae (15). The largest genera are Fissidens (28), Cololejeunea (17), Lejeunea (10), Syrrhopodon (9), Macromitrium (8) and Frullania (8). Twenty-nine families are represented by a single species. Hong Kong is the only confirmed locality for four Chinese endemic species. Phytogeographical patterns Fourteen categories of phytogeographical patterns were recognized for Hong Kong bryophytes (Table 1). The abbreviations for regions used in following text follow Van der Wijk et al. (1959–1969): As2 includes China, Mongolia, Japan, and Korea; As3 includes India, Pakistan, Sri Lanka, Myanmar, Thailand, Laos, Cambodia, and Vietnam; As4 includes Indonesia, Malaysia, the Philippines, and New Guinea. Two typical examples are given for each pattern or subpattern. 1 Cosmopolitan/Subcosmopolitan Mosses: nine taxa, 3.8%; Liverworts: seven taxa, 5.2%; Bryophytes: sixteen taxa, 4.3%. Wide global distributions. Bryum argenteum, Aneura pinguis. 2 Pantropical Mosses: twenty-nine taxa, 12.2%; Liverworts: nine taxa, 6.7%; Bryophytes: thirty-eight taxa, 10.2%.  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 Phytogeography of Hong Kong bryophytes 1331 Table 1 Phytogeographical patterns of Hong Kong bryophytes Patterns Subpatterns 1. Cosmopolitan 2. Pantropical 3. Palaeotropical 3a 3b 3c 3d 4. 5. 6. 7. Tropical Asian Tropical Asian–Tropical Australian–Oceanian Asian–Australian–Oceanian Eastern Asian 7a 7b 7c 8. Eastern & Southern Asian 9. Eastern Asian–Malesian 10. Eastern Asian–Indomalesian 11. Transpacific 12. Temperate 12a 12b 12c 13. Chinese Endemic 13a 13b 13c 14. Unknown Total Widely distributed throughout all tropical regions, in a few cases extending to subtropical regions. Calymperes erosum, Lejeunea flava. 3 Palaeotropical (Tropical African–Tropical Asian–Tropical Australian–Oceanian) Mosses: nineteen taxa, 8.0%; Liverworts: seventeen taxa, 12.7%; Bryophytes: thirty-six taxa, 9.7%. Distributed in all tropical regions except tropical America. This pattern can be divided further into four subpatterns on the basis of the eastern limits of distribution. 3a Tropical African–Tropical Asian Mosses: two taxa; Liverworts: five taxa; Bryophytes: seven taxa, 1.9%. Distributed from tropical Africa to tropical Asia, but not beyond New Guinea. Schlotheimia grevilleana, Chandonanthus birmensis. 3b Tropical African–Tropical Asian–Tropical Australian Mosses: five taxa; Liverworts: 0 taxa; Bryophytes: five taxa, 1.3%. Distributed from tropical Africa to tropical Asia and Tropical Australia, but not reaching the Oceanian Islands. Mitthyridium flavum.  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 Mosses (%) 9 29 19 2 5 3 9 14 13 33 40 3 31 6 7 5 14 11 26 4 16 6 14 4 9 14 4 238 (3.8%) (12.2%) (8.0%) (5.9%) (5.5%) (13.9%) (16.8%) (2.9%) (2.1%) (5.9%) (4.6%) (10.9%) (5.9%) (1.7%) Liverworts & Hornworts (%) 7 9 17 5 0 6 6 6 9 12 33 2 22 9 3 4 9 2 18 2 11 5 0 0 0 0 5 134 Bryophytes (%) (5.2%) (6.7%) (12.7%) 16 (4.3%) 38 (10.2%) 36 (9.7%) (4.5%) (6.7%) (9.0%) (24.6%) 20 22 45 73 (5.4%) (5.9%) (12.1%) (19.6%) (2.2%) (3.0%) (6.7%) (1.5%) (13.4%) 10 9 23 13 44 (2.7%) (2.4%) (6.2%) (3.5%) (11.8%) (0.0%) 14 (3.8%) (3.7%) 9 (2.4%) 372 3c Tropical African–Tropical Asian–Oceanian Mosses: three taxa; Liverworts: six taxa; Bryophytes: nine taxa, 2.4%. Distributed from tropical Africa to tropical Asia and the Oceanian Islands, but not reaching Australia. Callicostella papillata, Cololejeunea floccosa. 3d Tropical African–Tropical Asian–Tropical Australian– Oceanian Mosses: nine taxa; Liverworts: six taxa; Bryophytes: fifteen taxa, 4.0%. Distributed from tropical Africa to tropical Asia, Tropical Australia, and the Oceanian Islands. This is the most prominent component of this pattern. Rhodobryum giganteum, Mastigophora diclados. 4 Tropical Asian (As3 & As4) Mosses: fourteen taxa, 5.9%; Liverworts: six taxa, 4.5%; Bryophytes: twenty taxa, 5.4%. Widely distributed in tropical regions from Sri Lanka and India through Indochina, the Malay Peninsula, and Indonesia, but not reaching Australia or the Oceanian Islands. A few taxa reach subtropical China or Southern Japan. Fissidens javanicus, Lejeunea cocoes. 1332 L. Zhang and R. T. Corlett 5 Tropical Asian (As3 & As4)–Tropical Australian– Oceanian Mosses: thirteen taxa, 5.5%; Liverworts: nine taxa, 6.7%; Bryophytes: twenty-two taxa, 5.9%. Widely distributed from Sri Lanka, India, Indochina, the Malay Peninsula, and Indonesia, to tropical Australia and/ or the Oceanian Islands. The northern distribution boundary is generally not beyond the provinces of the South China coast. Syrrhopodon trachyphyllus, Plagiochila javanica. Mainly distributed from Sri Lanka, India to Indochina and Eastern Asia, but not reaching Malesia (As4). Brotherella erythrocaulis, Frullania moniliata. 6 Asian (As2, As3 & As4)–Australian–Oceanian Mosses: thirty-three taxa, 13.8%; Liverworts: twelve taxa, 9.0%; Bryophytes: forty-five taxa, 12.1%. This is the second largest pattern in the local bryoflora. It differs from Pattern 5 by its northern boundary of distribution reaching temperate Asia, and usually covers the whole of China, Japan, Korea, the Russian Far East and Siberia. Neckeropsis obtusata, Lejeunea parva. 10 Eastern Asian–Indomalesian (As2, As3 & As4) Mosses: fourteen taxa, 5.9%; Liverworts: nine taxa, 6.7%; Bryophytes: twenty-three taxa, 6.2%. Distributed widely in Asia, but sometimes scattered. Taxiphyllum arcuatum, Drepanolejeunea angustifolia. 7 Eastern Asian (As2) Mosses: forty taxa, 16.8%; Liverworts: thirty-three taxa, 24.6%; Bryophytes: seventy-three taxa, 19.6%. This pattern is the most prominent one in the local bryophyte flora. Distributed generally from the Eastern Himalayas to Japan, occasionally reaching southward to central Indochina or the Philippines, northward to Russian Siberia or the Far East. It can be divided into three subpatterns. 7a Himalayan–Southwestern China Mosses: three taxa; Liverworts: two taxa; Bryophytes: five taxa, 1.3%. Distributed mainly from the Eastern Himalayas to Southwestern China, occasionally extending to East China, North Indochina or the Philippines, but not Japan. Fissidens jungermannioides, Plagiochila fordiana. 7b Southwestern China–Japan Mosses: thirty-one taxa; Liverworts: twenty-two taxa; Bryophytes: fifty-three taxa, 14.2%. Mainly distributed from Southwestern China to Japan, occasionally extending to North Indochina or the Philippines, but not the Eastern Himalayas. Stereodontopsis pseudorevoluta, Haplomitrium mnioides. 7c Himalayan–Japan Mosses: six taxa; Liverworts: nine taxa; Bryophytes: fifteen taxa, 4.0%. Distributed through the whole region from the Eastern Himalayas to Japan, occasionally extending to North Indochina or the Philippines. Meteorium subpolytrichum, Bazzania sikkimensis. 8 Eastern & Southern Asian (As2 & As3) Mosses: seven taxa, 2.9%; Liverworts: three taxa, 2.2%; Bryophytes: ten taxa, 2.7%. 9 Eastern Asian–Malesian (As2 & As4) Mosses: five taxa, 2.1%; Liverworts: four taxa, 3.0%; Bryophytes: nine taxa, 2.4%. Mainly distributed in Eastern Asia and Malesia, not beyond the Himalayas westward. Fissidens geppii, Lepidozia fauriana. 11 Transpacifics Mosses: eleven taxa, 4.6%; Liverworts: two taxa, 1.5%; Bryophytes: thirteen taxa, 3.5%. This pattern is mainly distributed disjunctly in East Asia and America, but sometimes extending to Australia or the Oceanian Islands. Taxiphyllum taxirameum, Plagiochila sciophila. 12 Temperate Mosses: twenty-six taxa, 10.9%; Liverworts: eighteen taxa, 13.4%; Bryophytes: forty-four taxa, 11.8%. This is the third largest pattern in the local bryophyte flora. Three subpatterns can be recognized as follows. 12a Eurasian Temperate Mosses: four taxa; Liverworts: two taxa; Bryophytes: six taxa, 1.6%. Distributed mainly in temperate Eurasia, with a few taxa extending to North Africa or subtropical regions. Plagiothecium nemorale, Calypogeia arguta. 12b North Temperate Mosses: sixteen taxa; Liverworts: eleven taxa; Bryophytes: twenty-seven taxa, 7.3%. Mainly distributed throughout the north temperate regions. Plagiothecium cavifolium, Trichocolea tomentella s. lat. 12c North and South Temperate Disjunct Mosses: six taxa; Liverworts: five taxa; Bryophytes: eleven taxa, 3.0%. Mainly distributed in temperate regions of the northern and southern hemispheres. Racomitrium fasciculare, Anthoceros punctatus. 13 Chinese Endemic Mosses: fourteen taxa; 5.9%; Liverworts: 0 taxa; Bryophytes: fourteen taxa, 3.8%. Distributions that do not extend beyond China. Three subpatterns can be recognized.  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 Phytogeography of Hong Kong bryophytes 13a Endemic to Hong Kong Mosses: four taxa; Liverworts: 0 taxa; Bryophytes: four taxa, 1.1%. Presently only known from Hong Kong. Macromitrium brevituberculatum, M. subincurvum, M. tuberculatum, and Syrrhopodon hongkongensis. 13b Endemic to South China Mosses: nine taxa; Liverworts: 0 taxa; Bryophytes: nine taxa, 2.4%. Distributed in provinces of the South China coast: Fujian Province, Guangdong Province, Guangxi Province, Hainan Province, Hong Kong, Taiwan Province, and Yunnan Province. Caduciella guangdongensis, Dicranella coarctata var. torrentium, Macromitrium heterodictyon, and Syrrhopodon chenii, plus the four species of 13a. 13c Chinese Endemic Mosses: fourteen taxa; Liverworts: 0 taxa; Bryophytes: fourteen taxa, 3.8%. Distributed in most regions of China. Campylopus taiwanensis, Fauriella tennerima, Pseudobarbella angustifolia, Schlotheimia pungens, and Trichostomum hattorianum, plus the nine species of 13b. 14 Unknown Mosses: four taxa, 1.7%; Liverworts: five taxa, 3.7%; Bryophytes: nine taxa, 2.4%. Either data deficient or cannot be allocated to one of the above patterns. Haplohymenium pseudo-triste, Cololejeunea hispidissima. Comparisons with other regions Comparisons were made between the bryoflora of Hong Kong and those of six Chinese provinces and five other regions for which comparable data were available (Table 2). The most similar regions to Hong Kong are Hainan (Krober’s % similarity ¼ 54.7%), Taiwan (51.9%) and Japan (46.6%). The same patterns hold for the mosses alone, but Jiangxi Province shows the highest similarity (56.7%) for the liverworts. DISCUSSION The phytogeography of the Hong Kong bryoflora The composition of the bryoflora is consistent with Hong Kong being on the northern climatic limits of the tropics. For the purposes of discussion, the fourteen phytogeographical patterns can be combined into three – Tropical, East Asian and Temperate – plus patterns that do not fit into any of these three categories (Table 3). Although the Tropical element is the largest of the three, contributing a third of the total taxa, the total number of non-tropical taxa (i.e. East Asian plus Temperate) is greater. As would be expected for a marginal location, the proportion of Tropical taxa declines with altitude. Sufficient altitudinal data are only available  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 1333 for mosses, where Tropical taxa were considerably more prominent below 500 m than above 700 m (Table 4). Examples of Tropical taxa only found below 500 m include Brachymenium exile, Bryum cellulare, Calymperes tenerum, Fissidens kinabaluensis, Pogonatum camusii, and Syrrhopodum spiculosus. Conversely, East Asian taxa are more diverse at higher altitudes, although there was no clear pattern for Temperate taxa. Temperate and East Asian taxa found only above 600 m include Herbertus aduncus, Entodon cladorrhizans, Rhodobryum giganteum, Plagiothecium cavifolium, P. nemorale, Racomitrium fasciculare, Polytrichastrum formosum, and Trachycystis microphylla. Several features of the Hong Kong bryoflora are typical of the wet tropics. The dominance of the family Lejeuneaceae among the liverwort flora is characteristic of tropical lowland floras elsewhere (Cornelissen & Gradstein, 1990; Gradstein, 1992), and several genera with their centres of evolution in tropical Asia are represented in Hong Kong, including Acroporium, Dicranoloma, Homaliodendron, Macrothamnium, Mitthyridium in the mosses, and Spruceanthus and Tuyamaella in liverworts. Epiphyllous bryophytes on living leaves are another characteristic feature of wet tropical forest communities (Richards, 1996) that is locally well developed in Hong Kong, with at least twentyseven liverwort species involved (Zhang et al., 1999; Zhang, 2003). On the contrary, the families Dawsoniaceae, Hypnodendraceae, Spiridentaceae and Garovaglioideae, which characterize tropical Asian rain forests (Gradstein & Pocs, 1989), do not occur in Hong Kong, while some typical temperate families, such as Grimmiaceae, Amblystegiaceae, Plagiotheciaceae, Hylocomiaceae and Brachytheciaceae do occur, mostly at high elevations. Three characteristic East Asian genera, Fauriella, Palisadula and Pilotrichoposis, occur in Hong Kong, emphasizing the East Asian aspect of the bryoflora (Deguchi & Iwatsuki, 1984; Gao & Cao, 1992; Wu, 1992). The relatively high similarities between Hong Kong’s bryoflora and those of Hainan and Taiwan are not surprising, as these are the nearest regions with relatively complete checklists and also have climatic similarities with Hong Kong. The taxa shared between Hong Kong and Hainan are mostly Tropical, such as the Calymperaceae and Hookeriaceae. Taxa shared with Taiwan are also mainly Tropical, but include an increased proportion of East Asian and Temperate taxa. With Japan, in contrast, the majority of shared taxa are East Asian and Temperate. The surprisingly high similarity with Japan, despite its very different climate except in the extreme south of the archipelago, may partly reflect both the past historical geographic relationships and the greater completeness of Japan’s botanical inventory. The same factors may also explain the high similarity between the liverwort floras of Hong Kong and Jiangxi, despite considerable climatic differences. Unfortunately, there is no published bryophyte inventory for the adjacent Chinese province, Guangdong, which is bisected by the Tropic of Cancer. However, the bryoflora of the southern coastal regions of the province is generally similar to that of Hong Kong, while there are fewer tropical 1334 L. Zhang and R. T. Corlett Table 2 Phytogeographical similarities between the bryofloras of Hong Kong and other areas No. of taxa shared with Hong Kong (Krober’s % similarity) No. of taxa Countries/ regions China Hong Kong Hainan Hunan Land area (km2) Mosses Liverworts Total  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 Mosses Liverworts Total References Zhang (2003) Lin et al. (1994), Zhang (1996), Zhu & So (2001) Koponen et al. (2000), Rao et al. (1997), Tian (1999), Zhu & So (2001) Fang et al. (1998), Zhu & So (2001) Piippo (1990), Redfearn et al. (1996), Zhu & So (2001) Gao & Cao (2000), Li (2002), Piippo et al. (1998), Redfearn et al. (1996), Zhu & So (2001) Redfearn et al. (1996), Zhu et al. (1998), Zhu & So (2001) Scott & Bradshaw (1985), Streimann & Curnow (1989) Frahm et al. (1990), Menzel (1988), Touw (1978) Furuki & Mizutani (1994), Matsui (1995), Zhu & So (2001) He (2000) Piippo & Tan (1992), Tan & Engel (1986), Tan & Iwatsuki (1991), Tan et al. (2000) 1100 33,920 211,829 238 247 249 134 165 94 372 412 343 – 138 (56.9%) 78 (32.0%) – 76 (51.4%) 47 (42.5%) – 214 (54.7%) 125 (35.0%) Jiangxi Taiwan 166,722 36,000 192 907 90 497 282 1404 77 (36.2%) 190 (50.4%) 61 (56.7%) 115 (54.5%) 138 (43.0%) 305 (51.9%) Yunnan 380,000 912 606 1518 162 (42.9%) 99 (45.1%) 261 (43.7%) Zhejiang 101,800 580 263 843 128 (37.9%) 81 (45.6%) 209 (40.5%) 7,682,300 1168 674 1842 72 (18.2%) 31 (13.9%) 103 (16.6%) Borneo Japan 743,330 369,883 649 1183 623 612 1272 1795 95 (27.3%) 177 (44.7%) 54 (24.5%) 118 (53.7%) 149 (25.9%) 287 (46.6%) Thailand Philippines 514,000 299,000 652 716 – 532 – 1248 136 (39.0%) 132 (36.9%) – – 198 (34.5%) Australia 66 (30.8%) Phytogeography of Hong Kong bryophytes Table 3 Summary of the phytogeographical patterns of the Hong Kong bryoflora (with patterns 1 and 14 excluded) Summary patterns Tropical East Asian Temperate Others Total Table 4 Phytogeographical patterns of the mosses of Hong Kong occurring < 500 and > 700 m above sea-level Altitudinal ranges Mosses (%) 75 54 37 59 225 (33.3%) (24.0%) (16.4%) (26.2%) Liverworts (%) 41 33 20 28 (33.6%) (27.0%) (16.4%) (23.0%) 122 Tropical (%) The biogeographical position of Hong Kong The location of the biogeographical boundary between the East Asian tropics and Palaearctic (or Holarctic) is controversial because there are no climatic or physical barriers to dispersal between the regions. In the absence of an intervening arid zone, some aspect of temperature is likely to be the ultimate control on the northern limits of distribution for most taxa of tropical origin. For birds and mammals, which are relatively independent of air temperatures, the northern boundary of the tropical region (the Oriental or Indomalayan Region) in East Asia is generally set at around 35
N (Corbet & Hill, 1992; Inskipp et al., 1996) and Hong Kong’s fauna is almost entirely tropical (Dudgeon & Corlett, 1994). The same seems to be true for invertebrates (e.g. Hong Kong’s dragonflies and butterflies; Wilson, 1995; Bascombe et al., 1999), but Hong Kong also lacks some characteristic tropical lowland invertebrate groups, such as the stingless bees (Meliponini). Despite Takhtajan’s (1986) premature assignment of Hong Kong to his Holarctic floral kingdom, Hong Kong’s vascular plant flora is also strongly tropical at the generic level, with 82.5% of genera showing tropical patterns of distribution (Xing et al., 1999). The bryophytes, therefore, seem to be unusual in the relatively low proportion of tropical taxa in the flora. This may reflect a greater sensitivity to temperature in small plants that can neither insulate themselves against temperature changes nor spend the cold season in protected microhabitats. However, in contrast to the flowering plants, where visible frost damage to the leaves and shoots of tropical taxa occurs in exceptional cold spells (Corlett, 1992), cold damage to bryophytes in Hong Kong has not been observed. An alternative explanation for the low proportion of tropical bryophytes in Hong Kong is that, in contrast with most other  2003 Blackwell Publishing Ltd, Journal of Biogeography, 30, 1329–1337 Bryophytes (%) Patterns in Table 1 116 87 57 87 (33.4%) (25.0%) (16.4%) (25.1%) 2, 3, 4, 5 7, 13 11, 12 6, 8, 9, 10 Temperate (%) Uncertain (%) 347 East Asian (%) Taxa occurring only < 500 m 27 (42.2%) 12 All taxa occurring < 500 m 57 (36.5%) 33 Taxa occurring only > 700 m 2 (10.0%) 7 All taxa occurring > 700 m 28 (25.9%) 26 and more temperate species in the northern mountainous region. For example, species of Sphagnum are easily found in the highlands of northern Guangdong, and members of the Calymperaceae are rare. 1335 (18.7%) 14 (21.9%) 11 (21.2%) 24 (15.4%) 42 (35.0%) 4 (20.0%) 7 (24.1%) 16 (14.8%) 38 Total (17.2%) 64 (26.9%) 156 (35.0%) 20 (35.2%) 108 major taxonomic groups, the bryophytes are not markedly more diverse in the tropics than at higher latitudes. For vascular plants, vertebrates and most invertebrate groups, the pool of tropical species available in East Asia is much larger than the pool of non-tropical species, while this does not appear to be true for bryophytes. As a result, a location on the climatic margins of the tropics would be expected to support a lower proportion of tropical species for bryophytes than for other taxonomic groups. Preston & Hill (1999) also noted the more northerly distributions of mosses and liverworts than flowering plants in the Northern Hemisphere. Previous reviews of bryophyte geography have differed in the region to which Hong Kong was assigned. Van der Wijk et al. (1959–1969) placed Hong Kong within the region As2, which included China, Mongolia, Japan and Korea, but Schofield (1992) placed it well within the Palaeotropical Kingdom. In a discussion of bryophyte phytogeographical regions of China, Chen (1963) placed Hong Kong in the Lingnan Distinct, which includes the whole of Hainan and Taiwan, most of Guangdong, South Fujian, Guangxi, and Yunnan. Based on the preceding analysis, the simplest conclusion is that Hong Kong is on the northern margins of the Palaeotropical Kingdom. Bryophyte diversity in Hong Kong The bryoflora of Hong Kong appears to be exceptionally rich for its small area (Table 2), particularly in view of the long history of massive human impacts. Although this diversity may partly reflect the high intensity of collection effort, another factor must be the wide range of habitat types within Hong Kong’s 1100 km2. This includes frost-free (at least for the last century) coastal and inland lowland habitats as well as frost-prone montane habitats, providing suitable growing conditions for both tropical and non-tropical species. Moreover, while most of Hong Kong is now covered in anthropogenic habitats, such as grassland, shrubland and urban areas, which support a low diversity of bryophytes, 1336 L. Zhang and R. T. Corlett enough forest remains, except at the lowest altitudes, to provide adequate microhabitats for the largely forestdependent native bryoflora. This is in stark contrast to the vertebrate fauna, where the forest patches are too small to support viable populations of forest-dependent species (Corlett, 2000). Four moss taxa are currently only known from Hong Kong: the recently described Syrrhopodon hongkongensis and three species, Macromitrium brevituberculatum, M. subincurvum and M. tuberculatum, which have not received any revision work since they were established about 70 years ago. The statuses of the latter three species are still uncertain. ACKNOWLEDGMENTS Sincere thanks are extended to Dr Lawrence Chau and Ms Gloria Siu for their invaluable support during the course of study, Ms Laura Wong for her technical help, Dr Benito Tan for his constructive comments on an earlier draft of this paper, and two anonymous reviewers for their helpful comments on the manuscript. The study was financially supported by a postgraduate studentship from the University of Hong Kong. Li Zhang would like to thank Kadoorie Farm & Botanic Garden for supplying him the working and living convenience from November 1997 to April 2000. REFERENCES Bascombe, M.J., Johnston, G. & Bascombe, F.S. 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(1997) Forest and forest succession in Hong Kong, China. Journal of Tropical Ecology, 14, 857–866. BIOSKETCHES Li Zhang is a bryologist at the South China Institute of Botany, the Chinese Academy of Sciences, Guangzhou, China. He is interested in the taxonomy, biogeography, ecology, and conservation of bryophytes from South China. Richard T. Corlett is an Associate Professor in the Department of Ecology & Biodiversity, University of Hong Kong. His major research interest is the ecology and conservation biology of degraded tropical landscapes.