Distribution And Conservation Status Biology

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Wenchengia alternifolia Lamiaceae is an enigmatic plant species endemic to Hainan Island, China. For most of the past half-century, it is known mainly from two collections and was once suggested to be extinct until a remnant population was rediscovered in 2010 by the authors. We expanded field surveys and finally located two subpopulations and counted a total of 66 individuals. Thus W. alternifolia represents one of the most endangered species within Lamiaceae and falls within the Critically Endangered category of the Red List. Observations of dried and broken infructescences with nutlets along mountain streams indicate seed dispersal by water. The development of tropic agriculture in Hainan is the main threat to the species. To conserve this species more effectively we recommend that: (1) the remnant subpopulations and their habitats require urgent protection and monitoring, (2) ex-situ conservation and reintroduction should be implemented to rescue the species at the edge of extinction.

Keywords conservation strategy, endemic species, ex-situ conservation, habitat destruction, rediscovery.

Hainan, the second largest island of China with an area of approximately 33, 900 km2 (Fig. 1), harboring a total of ca. 4800 species of vascular plants (Xing et al., 2012) and the best preserved tropical forests in China (Deng et al., 2008), deserves a major priority for conservation. However, the island has experienced extensive deforestation over the past several decades, posing major threats to its biodiversity (Francisco-Ortega et al., 2010). As one of the seven monotypic genera endemic to the island (Francisco-Ortega et al., 2010), Wenchengia C. Y. Wu & S. Chow (Lamiaceae) and the sole member W. alternifolia C. Y. Wu & S. Chow was described and established on the basis of two collections in the 1930s (Wu & Chow, 1965). For most of the past half-century, W. alternifolia is known only from the two collections and considered as one of the most enigmatic genera in the mint family (Cantino & Abu-Asab, 1993). It was once suggested to be extinct (Harley et al., 2004) until a remnant population was rediscovered in 2010 (Li et al., 2012). However, such a species at the edge of extinction has not been included in the 2012 Red List (IUCN, 2012) or List of National Protected Key Wild Plants (First Batch) (August 4, 1999), and merely categorized as vulnerable in the China Species Red List (Wang & Xie, 2004), possibly because of insufficient information. To effectively protect this enigmatic species, this study is designed to provide detailed population information on Hainan Island and evaluate the major threats to this species. Based on the updated data, we proposed several conservation strategies for the species.

The rediscovered population of Wenchengia alternifolia is located in a stony valley (Shuangximu valley, 18°43′41.26″N, 110°05′9.01″E) of the Nanlin State Forestry Center, Xinglong Town, Wanning City (Fig. 1), Hainan province of China. With an area of ca. 1500 m2 and at an altitude of ca. 100-300 m, the valley is surrounded mainly by areca, rubber and pineapple plantations. Several mountain streams flow into the valley and flood periodically during the rainy seasons of July to November. The population of W. alternifolia is separated into two parts by a 15-meter fall and a pond of ca. 80 m2 below the fall. The individuals above the fall is shaded by a small and dense forest of ca. 300 m2 (Plate 1a) and accompanied mostly by Rubiaceae and Euphorbiaceae shrubs. The individuals under the fall is scattered among huge stones (Plate 1b) and growing out from moist stone cracks and cliffs (Plate 1c).

With an expectation to discover more populations of W. alternifolia, we closely examined the records from all the four known specimens: the types (How 7368, one sheet deposited in Herbarium of the South China Botanical Garden, the Chinese Academy of Sciences, IBSC; another sheet deposited in Harvard University Herbaria, HUH), paratypes (Liu 28220 deposited in IBSC and HUH), and others (Deng 3079, in IBSC, and Hu 9017, in Herbarium of the Missouri Botanical Garden, MO). The records of How 7368 and Deng 3079 indicate they were both collected from "Shuangximu valley near Xinglong Town", the same locality as the surviving population. Our endeavor to locate the precise localities of both Liu 28220, recorded as "Nanniuling valley in Baoting County", and Hu 9017, simply documented as from "Hainan Island" was in vain, however. The rediscovered Shuangximu valley population is thus probably the only one survived for W. alternifolia. The species represents one of the most endangered species in China and falls within the Critically Endangered category (CR, based on criteria B2a) of the Red List guidelines of the World Conservation Union (IUCN, 2001).

Wenchengia alternifolia are subshrubs 15 - 40 cm in height, and usually exhibits a clumped structure, each clump consisting of several slender, leafy shoots. Most of the shoots are ascending into inflorescences, but some are much more flexible and trail along stone cracks to form clones (Li et al., 2012). Allowing for its growth structure, we counted a total of 66 individuals within the remnant populations, with 45 in subpopulation â…  and 21 in subpopulation â…¡. The number of shoots per individual is 1 - 25 (mean 5.6, n = 30). All adult individuals fruited normally, producing schizocarpic fruits. The number of fruits per reproductive shoot are 6 - 45 (mean = 17, n = 50); a fruit comprises four dry nutlets or sometimes only the upper two develop. Accordingly, an individual could generate 190 - 380 mature nutlets, suggesting seed output is not the main limiting factor of population viability. However, only a small proportion of young plants were observed in the locations, implying a low rate of seed germination, a possible result of the harsh stony habitat of W. alternifolia.

We observed fallen branches and dried infructescence of W. alternifolia along mountain streams, and several immature or undeveloped nutlets hung outside calyx in the infructescence (Plate 1d). W. alternifolia has a unique type of nutlet attachment in Lamiaceae: four dry nutlets in a fruit attached in pairs to the receptacle by two slender, bifurcating stalks; each stalk has two white funicles which are very flexible so that the nutlets hung outside through calyx crack (Li et al., 2012). The nutlets of W. alternifolia are broadly obovoid, dorsiventrally flattened and apically tuberculate and pubescent (Li et al., 2012), which may enable the nutlets to float in water. Thus fruit dispersal of W. alternifolia may strongly depend on water flow. When the rainy season comes, torrential rains or fierce flooding could break the funicles, then carry the nutlets to moist stone cracks or cliffs where is suitable for the nutlets staying and germinating. This might explain the appearance of W. alternifolia in high stone cracks and cliffs along the valley.

The destruction of habitat is the major threat to species survival around the world. By the 1950s, approximately 25.5% of Hainan was covered by forests, but by 1998 this figure had decreased to 8.7% (Compilation Group of China's Biodiversity, 1998). Extensive changes in land use, mainly from the expansion of tropical plantations, as well as rapid development of urbanization, mining and tourism industries (Guo et al., 2006), has resulted in a dramatic transformation of once-contiguous forests into small and isolated fragments. Based on the specimen How 7368 and Liu 28220, the habitats of W. alternifolia are "on the roadside of Xinglong Town" or "under dense rainforest", which indicates that W. alternifolia and its habitat was not so rare in 1930s compared to the present day. However, extensive changes in land use could have eradicated most W. alternifolia populations, and only one population described here have escaped from the disaster, possibly due to the unsuitability of the stony valley for tropical plantations.

Given the extremely limited population size and harsh habitat of W. alternifolia, strict protection and monitoring of the two extant subpopulations should be a primary step toward long-term survival of the enigmatic species. It is particularly important to halt the persistent disturbance from tropical agricultural activities. Any more loss of individuals and habitat damage will be irreparable for W. alternifolia. Second, ex-situ conservation and reintroduction in historical range is essential for the protection of W. alternifolia. Five plants of W. alternifolia have been transplanted to a greenhouse in SCBG in April 2010, and they all grow well and flower normally, indicating ex-situ conservation could be an effective strategy to rescue this species. Forthcoming studies of genetic variation of all remnant individuals will be helpful for further identification of critical individuals and for planning the conservation of the species' genetic diversity.

In summary, W. alternifolia is a critically endangered species, with only 66 individuals in two known subpopulations, being restricted to a small and harsh area surrounded by tropical plantations. To conserve this species more effectively, we recommend that: (1) the presently known subpopulations and their habitats require urgent protection and monitoring, (2) ex-situ conservation and reintroduction could be an effective strategy for rescuing the species at the edge of extinction.

Acknowledgements

The authors are grateful to Mr. Zhong-Hui Ma and Zhu-Qiu Song for field assistance. This work was supported by National Natural Science Foundation of China (Grant No. 30970182, 31170184) and the Chinese Academy of Sciences Knowledge Innovation Program (Grant No. KSCX2-EW-Z-6-6).

Article name: Distribution And Conservation Status Biology essay, research paper, dissertation