Conservation and reintroduction of Euryodendron excelsum Chang, a critically endangered plant in south China
Euryodendron excelsum H. T. Chang is an evergreen tree belonging to the genus Euryodendron of the family Theaceae. Euryodendron is a monotypic genus and E. excelsum is the only described species. Euryodendron excelsum is endemic to South China, limitedly distributing in the Bajia town of Yangchun county, Guangdong province, and the Pingnan county and Bama county of Guangxi province. Exhaustively field investigations in the last decade have indicated that plants in the above two distributing sites of Guangxi province were totally extinct. Only one remaining population survives in the Bajia town of Guangdong province. About 100 plants including 10-14 old trees occur in this population and they are yet under threats due to the increasing agriculture activities, local tourism and habitat fragments. E. excelsum has been listed as critically endangered in 2008 IUCN Red List of Threatened Species and also in China Plant Red Data Book.
E. excelsum usually occurs in open forest on hilly slopes or in valleys between 40 and 400m. It can grow as high as 15-25m. The accompanied species in E. excelsum community mostly are evergreen plants such as Melia dubia, Cinnamomum camphora, Camellia oleifera, Ficus heteram orphan, and Fluggea virosa. Like some other Theaceae plants, the bark of E. excelsum is grayish brown or grayish black, with reddish brown or pale grayish brown branchlets and elliptic or oblong-elliptic leaves. The white flower of E. excelsum is bisexual, flowering from September to November. Its berried fruit becomes bluish black when mature between October and January the following year, with 2 or 3 seeds per locule.
Progress has been made in understanding the natural distribution, population genetic diversity, seeds dispersals and propagation method of E. excelsum. RAPD analysis on 14 samples collected from the Bajia population has showed a comparably lower level of genetic diversity than those observed in other Theaceae plants such as Apterosperma oblate and Camellia changii. The reduced population size due to habitat fragment may have already impacted the gene pool integrity of this endangered species. Sexual reproduction is predominant in wild E. excelsum population and birds are the main transporter for seeds dispersals. Increasing harvesting activities and habitat fragments have influenced birds inhabiting the E. excelsum forest, which, in turn, result in reduced seeds dispersals. Previous studies have showed that the fresh mature seeds of E. excelsum can normally germinate with good water conditions. About 50% of seeds germinate during 8~25 days and half of them can be transplanted after one year. However, the germinating rates of seeds reduce quickly when they have been stored in a long time without water. The water conditions thus are one key factor limiting seedlings occurrence in disturbed habitats or open forest in nature. Asexual propagation by cutting shoots has been done and only 16% of them can successfully root when they soaked by the 100mg/L indolebutyric acid solution. However, our recent experiments conducted in SCBG give evidence that layering cutting is a better way for cutting propagation. More than 20 plants have already been successfully propagated by this way, and all of them are very useful as material basis for future conservation and reintroduction activities. Collectively, both limited ecological adaptability of this species and increasing anthropologic disturbance have greatly impacted the normally reproduction and regeneration of E. excelsum in wild. Particularly, the severely forest harvesting activities since 1950s in China have largely resulted in habitat loss and fragments of this species.
Unfortunately, no enough conservation activities have been performed for rescuing this disappearing plant. Although positive efforts have been made by local government to conserve several old E. excelsum trees in the Bajia town, many other remnants or young seedlings are under threats. The original habitats of E. excelsum are severely fragmented and over explored, and are not adapted for the long term living of this species. Ex situ conservation on this endangered species is needed urgently. Artificial propagation of E. excelsum plants is critical to provide materials for future reintroduction activities. With an ultimately target of the restoration of E. excelsum plants in wild, the Ehuangzhang Natural Reserve in Bajia town is the best place for reintroduction because it is under effective management without seriously anthropologic disturbance. Both ex situ conservation and the successive reintroduction would be performed. Aided by local government and Natural Reserve, we also expect to improve the public awareness on plant diversity conservation of local people and students.
This project will focus on or be related to the GSPC targets 5, 7, 8 and 14. It is well consistent with the context of in situ and ex situ conservation of threatened species in the most important areas and improving conservation activities incorporated into communication, educational and public awareness programmes.
As a plant belongs to the monotypic genus Euryodendron, E. excelsum is morphologically closed to the genera Cleyera and Eurya in Ternstroemoideae of the family Theaceae. Thus, it is especially important to our understanding on the origin and evolutionary relevance of the taxa included in Ternstroemoideae of the family Theaceae.
The area of Yangchun county, where the E. excelsum population distributed, is a potential biodiversity center, particularly for the gathered distribution of many endemic rare and endangered plants such as Apterosperma oblata, Acidosasa chinensis, and Diplopanax stachyanthus. A natural reserve named Ehuangzhang Natural Reserve has begun to set up in Bajia town for conservation of these important and threatened plants. The project is thus important for development of models with protocols for plant conservation and ecological restoration in the natural reserve area.
The natural distribution of E. excelsum trees in Bajia town
(Partner: South China Botanical Garden, CAS)