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Tropical China plant diversity, ecology and conservation--a glimpse at the current state.

China is known for its rich plant diversity, especially the mountain flora in the west and the eastern temperate area (Huang, 2011). In contrast, plant diversity and plant species conservation challenges in tropical China are less well known. Tropical China includes Hainan Island, Guangdong, Guangxi, and Yunnan provinces (Zhu, 2017). Southeast Asia's tropical limestone region, which includes parts of southern China, is rich in biodiversity and high in endemism (Clements et al., 2006). However, plant diversity, ecology and conservation issues in the Chinese tropical karst region, which is recognized as the world's largest limestone area (Pu et al., 2017; Zhang et al., 2017), are especially understudied.

In this special issue we focus on botanical studies in tropical China, with an emphasis on the tropical limestone flora. This special issue is an outcome of the recent joint tropical botany conference between the College of Tropical Agriculture and Forestry, Hainan University and the International Center for Tropical Botany at Florida International University.

Two articles describe the biology of unique karst features. Pu et al. (2017) review research on tiankengs, a recently recognized and distinct limestone feature that consists of a large (> 100 m diameter) depression enclosed by vertical walls/cliffs. China has the greatest abundance of these features in the world, where they are concentrated in the southwestern region. After discussing ideas about the geologic origin and evolution of these features, Pu et al. (2017) also describe floral and faunal diversity, as these habitats, which they compare to islands, harbor many unique and threatened species. They report on the biodiversity of 12 tiankengs and discuss threats to these unique habitats. Pu et al. (2017) conclude that understanding how physical, ecological and human-induced processes dictate or influence the dynamics of the tienkeng ecosystems is limited, and more coordinated interdisciplinary research is needed.

The second unique karst feature examined in this issue is the karst mountain Mt. Erxianling, which is found on Hainan Island but was not explored botanically until the late 1980s. Although most of Hainan is not karst, Mt. Erxianling is an east-west limestone outcrop in the western part of the island that reaches heights of >1000 m. Zhang et al. (2017) review studies of Mt. Erxianling vegetation made over the decade between 2003 and 2013. They recognize five forest types, summarize the results of surveys of vegetation plots established in each type, and describe the vegetation's biogeographic affinities. They also review the status of endemic species found during these recent botanical surveys and summarize the conservation status of these species. They also discuss the existing threat from mining that results in extensive habitat destruction in and around Erxianling, which has not enjoyed protection status at a meaningful level until very recently. Increasing recognition of the unique ecological status of this area, as documented here, however, has resulted in recent conservation advances for Erxianling. With support from Kadoorie Conservation China, a Hong Kong-based biodiversity NGO, a reserve station was constructed in 2009, and as of 2016, Exianling is being gazetted as a formal provincial nature reserve, and habitat destructive activities at a gold mine in Exianling have been stopped (Zhang et al., 2017).

One of the major plant groups of horticultural importance in the tropical limestone area is the gesneriads. Ling and colleagues (2017) studied the pattern of distribution and pollination strategies of Gesneriaceae from Hainan Island, the largest tropical island of China, as compared to the surrounding regions, including mainland China and Southeast Asia. They discuss the evidence for the divergence of Old and New World Gesneriaceae. Using a dated phylogeny of most species from Hainan Island and their closest relatives, a closer historical relationship of Hainan Island with Southeast Asia is found. This relationship is also supported by the geological history of the island.

Orchids are another major plant group of both medicinal, horticultural and ecological importance in the tropics. While the Orchidaceae is one of the largest plant families, many species are threatened by habitat alteration and over-harvesting (Cribb et al., 2003). Tropical epiphytic orchids constitute more than two-thirds of the orchid family (Atwood, 1986; Gravendeel et al., 2004), yet orchid germination studies have rarely focused on epiphytes. Yang and colleagues (2017) offer an in-depth look at factors affecting both in situ and ex situ germination of the Hainan Island endangered, endemic, epiphytic orchid Dendrobium sinense. They examined the effects of host tree bark, time of planting, and distance from conspecific adult plants on seed germination.

The results of their study offer insight into how to regenerate this endangered tropical orchid species in nature and in the lab.

Finally, Zhu (2017) reviews the status of tropical forests in China, first exploring the definition of frost-free zones and then examining the types of forests in these regions. The review shows that tropical forests in China resemble equatorial lowland rain forests in profile, physiognomical characteristics, and family composition. Chinese tropical forests, however, differ in composition among regions, as Zhu (2017) describes. Finally, the author reviews conservation threats to these forests, which include the replacement of forests with rubber and Eucalyptus plantations, forest fragmentation, and understory planting of cardamom in forests. Cultivation of this ginger is promoted as a cash crop that is compatible with forest preservation, as canopy trees are retained, but harvesting requires clearing of the sapling/seedling understory, thus preventing forest regeneration.

Together, this special issue provides insight into plant biodiversity and conservation in tropical China. The articles review current knowledge and understanding of important plant groups in these regions, provide data on geographic features unique to tropical China, and discuss forest composition and diversity in these areas. This issue also showcases issues of concern to Chinese plant scientists working in these regions and highlights conservation threats.

DOI: 10.1007/s12229-017-9180-7

Acknowledgements We would like to thank the moral, logistical and financial support from the leadership of the International Center for Tropical Botany at Florida International University and Hainan University during the two-year preparation period of this special issue. We acknowledge grant support from the National Natural Science Foundation of China (#31360146 to HL, 31670230 to MXR), and the Guangxi Science and Technology Bureau (grant no. 12217-04 to HL).

Literature Cited

Atwood, J. T. 1986. The size of the Orchidaceae and the systematic distribution of epiphytic orchids. Selbyana 9: 171-186.

Clements R., N. S. Sodhi, M. Schilthuizen & P. K. L. Ng. 2006. Limestone karsts of Southeast Asia: imperiled arks of biodiversity. Bioscience 56: 733-742.

Cribb, P. J., S. P. Kell, K.W. Dixon & R L. Barrett. 2003. Orchid conservation: a global perspective. In Dixon, K. W., S. P. Kell, R. L. Barrett, and P. J. Cribb. Eds. Orchid conservation. Natural History Publications, Kota Kinabalu, Sabah 1-24.

Gravendeel B., A. Smithson, F. J. W. Slik & A. Schuiteman. 2004. Epiphytism and pollinator specialization: drivers for orchid diversity? Philosophical Transactions of the Royal Society B: Biological Sciences 359: 1523-1535.

Huang, H. 2011. Plant diversity and conservation in China: planning a strategic bioresource for a sustainable future. Botanial Journal of the Linnea Society 166: 282-300.

Ling, S.-J., Q.-W. Meng, L. Tang & M.-X. Ren. 2017. Pollination syndromes of Chinese Gcsneriaceae: a comparative study between Hainan Island and neighboring regions. Botanical Review 1-15. doi:10.1007/s12229-017-9181-6.

Pu, G.-Z, Y.-N. Lv, G.-P. Xu, D.-J. Zeng & Y.-Q. Huang. 2017. Research progress on karst tiankeng ecosystems. Botanical Review 1-33. doi: 10.1007/s 12229-017-9179-0.

Yang, F.-S., A.-H. Sun, J. Zhu, J. Downing, X.-Q. Song & H. Liu. 2017. Impacts of host trees and sowing conditions on germination success and a simple ex situ approach to generate symbiotic seedlings of a rare epithytic orchid endemic to Hainan Island, China. Botanical Review (in press).

Zhang, R.-J., X.-S. Qin, H.-F. Chen, B. P. L. Chan, F.-W. Xing & Z. Xu. 2017. Phytogeography and Floristic Affinities of the Limestone Flora of Mt. Exianling, Hainan Island, China. Botanical Review (in press).

Zhu, H. 2017. The tropical forests of southern China and conservation of biodiversity. Botanical Review (in press).

Hong Liu (1,2,3,6) * Mingxun Ren (4) * Jennifer Richards (5) * Xiqiang Song (4)

(1) International Center for Tropical Botany and Department of Earth and Environment, Florida International University, 11200 SW 8th Street, Miami, FL 33099, USA

(2) Forestry College, Guangxi University, Nanning, Guangxi 540004, China

(3) Fairehild Tropical Botanic Garden, 11935 Old Cutler Road, Coral Gables, FL 33156, USA

(4) Institute of Tropical Agriculture and Forestry, Hainan University, Haikou 570228, China

(5) International Center for Tropical Botany and Department of Biological Sciences, Florida International University, 11200 SW 8th Street, Miami, FL 33099, USA

(6) Author for Correspondence; e-mail: hliu@fiu.edu

Published online: 5 April 2017
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Author:Liu, Hong; Ren, Mingxun; Richards, Jennifer; Song, Xiqiang
Publication:The Botanical Review
Geographic Code:9CHIN
Date:Mar 1, 2017
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