Status and conservation of Trigonobalanus doichangensis (Fagaceae)

Trigonobalanus doichangensis is a national rare and endangered plant of China. It is restricted to 4 sites in southwest Yunnan, China and 1 site in Chiang-Rai, northern Thailand. Investigations revealed that 4 community types are currently extant in Yunnan: isolated individuals, sprouting woods, mono-dominant forest and co-dominant forest. The habitats have been severely damaged and the populations there are facing a high risk of extinction. The adult phase of T. doichangensis is reached when a tree attains a height of about 4 m. The flowering and fruiting time varies slightly among populations and/or across the micro-habitats. In comparison with other fagaceous plants in the community, T. doichangensis has an inverse flowering and fruiting period from October through to May. Although microspore genesis and the development of male gametes are normal, the pollen does not germinate until at least 8 h culture. The highest germination rate was 37.8%. In addition, only 9.8% of the nuts contain well-developed seeds. Genetic variation analyzed with random amplified polymorphic DNA indicated that its total genetic diversity was 0.1600 and genetic diversity within populations was 0.0749, the coefficient of gene differentiation was 0.5320. Therefore, T. doichangensis has high genetic differentiation, a low level of genetic diversity and a poor gene flow compared to the other fagaceous species. It seems that habitat degradation, over exploitation and reproductive barriers, are most likely to be the factors threatening the species. However, it may be a combination of geographical catastrophic events, habitat deterioration, declining genetic diversity and physiological stress. Therefore, a practical conservation strategy for T. doichangensis is urgently needed.