Forest characteristics and population structure of Glyptostrobus pensilis, a globally endangered relict species of southeastern China

Abstract

The Chinese water pine Glyptostrobus pensilis is the sole surviving species of the genus Glyptostrobus. It is endemic to southern China, central Vietnam, and eastern Laos, and today it is nearly extinct in the wild. Forest community characteristics and population structure of G. pensilis in China have remained unknown up to now. We investigated six swamp forest stands and analyzed their forest community characteristics (i.e. vertical stratification, species composition, and diversity) and population structure, including the frequency distribution of DBH (diameter at breast height) and age-classes as found in Fujian Province, southeastern China. The vertical stratifications of all the forest stands were rather simple. The remaining wild specimens ranged from roughly 15 to some 357 years for an average of ca. 85 years, with only a few individuals less than 20 years old. Compared with the stands and populations of G. pensilis in Vietnam, the taxonomic compositions of the stands in the two regions were different, except for the dominant species-G. pensilis. The Shannon-Wiener index showed the overstory of each stand had much lower diversity (0.26 on average) in Fujian Province than that (1.97 on average) in Vietnam, whereas the diversity indices were about the same (around 2.41) for the understories in the two regions. Furthermore, we discovered 18 G. pensilis seedlings at the study sites in Fujian Province. This discovery demonstrates that G. pensilis regeneration is extremely poor and its populations are declining, although these populations are relatively healthier than those in Vietnam.

Keywords: Age-class; Fujian Province; Glyptostrobus; Regeneration; Relict plant; Vietnam.

Fig. 1

Distribution of fossil Glyptostrobus and extant Glyptostrobus pensilis. (A) Fossil occurrences of Glyptostrobus. (B) Present-day distribution of G. pensilis. (C) The locations of six populations of G. pensilis in Fujian, China. Red circles are the wild populations in Fujian and Vietnam, presented in this study. A pink circle indicates the population size is uncertain. P=Population. Data sources for (A): Miki, 1941, Miki, 1948, Tanai, 1961, Shimazu and Teraoka, 1962, Tanai and Suzuki, 1963, Matsuo, 1967, Ishida, 1970, Tanai, 1970, Hayashi, 1975, WGCPC (Writing Group of Cenozoic Plants of China), 1978, Guo and Li, 1979, Tanai, 1979, Chen et al., 1983, Fujita and Kasama, 1983, Tanai and Uemura, 1983, Hase, 1988, Matthews and Ovenden, 1990, Ina, 1992, Momohara, 1992, Liu et al., 1996, Jin and Sang, 1998, Geng et al., 1999, Uemura et al., 1999, Martinetto, 2001; Guo and Zhang, 2002, Greenwood et al., 2005, Yamakawa et al., 2008, Bozukov and Tsenov, 2012, Mathewes et al., 2016, PALEOBIDB (Paleobiological database), 2017. Data sources for (B): Electronic Supplementary Information S1.

Fig. 2

Glyptostobus pensilis forest stands in Fujian Province. (A) Seed cones of G. pensilis in July. (B) A swamp forest stand of G. pensilis in Shangloucun, Pingnan. (C) A swamp forest stand of G. pensilis in Shanlingcun, Youxi. (D) A swamp forest stand of G. pensilis in Dongshancun, Youxi, showing some dead trees. (E) A swamp forest stand of G. pensilis in Xianfengshan, Zhouning. (F) A seedling of G. pensilis growing on a fallen log. Photographs by Cindy Q. Tang.

Fig. 3

Frequency distribution of woody species based on height (H ≥ 1.3 m) in the six swamp forest stands in Fujian (A)−(F).

Fig. 4

Species diversity in the forest stand overstory and understory. (A) Number of species. (B) Reciprocal Berger–Parker Index (1/d). (C) Shannon–Wiener Index. Locations of each plot: Plot 1 at Shangloucun in Pingnan; Plot 2 at Lingfengcun in Pingnan; Plot 3 at Lingfenglu in Pingnan; Plot 4 in Dongshancun in Youxi; Plot 5 in Shanlingcun in Youxi; Plot 6 in Xianfengshan in Zhouning.

Fig. 5

Relationships between DBH and age for G. pensilis.

Fig. 6

Frequency distribution in DBH- and age-classes of Glyptostrobus pensilis in six swamp forest stands in Fujian. (A)–(F) Frequency distribution in DBH-classes; (G)–(L) Frequency distribution in age-classes.

Fig. 7

G. pensilis seedlings/saplings emergence for swamp forest stands of Fujian, 2016.

Fig. 8

A comparison of diversity of forest stands in Fujian and Vietnam. (A) The number of taxa respectively at the family, genus, and species levels for six stands in Fujian and two stands in Vietnam. (B) Sørensen's similarity index (beta diversity) at family, genus, and species levels between the forest stands in Fujian and Vietnam, respectively. (C) Shannon–Wiener index on average with standard deviation (SD) for the overstories and the understories of forest stands in Fujian and Vietnam.

Fig. 9

A comparison of the population structures of Glyptostrobus pensilis in Fujian (the six stands) and Vietnam (combined the two stands in Trap K'sor and Ea Ral). (A) Frequency distribution of height. (B) Frequency distribution of DBH. (C) Frequency distribution of Vitality. Data for the Vietnamese stands are from Averyanov et al. (2009).