Research Article |
Corresponding author: Runguo Zang ( zangrung@caf.ac.cn ) Academic editor: Anatoliy Khapugin
© 2020 Jihong Huang, Zhongjun Guo, Suying Tang, Wei Ren, Guangming Chu, Liping Wang, Ling Zhao, Ruoyun Yu, Yue Xu, Yi Ding, Runguo Zang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Huang J, Guo Z, Tang S, Ren W, Chu G, Wang L, Zhao L, Yu R, Xu Y, Ding Y, Zang R (2020) Floristic composition and plant diversity in distribution areas of native species congeneric with Betula halophila in Xinjiang, northwest China. Nature Conservation 42: 1-17. https://doi.org/10.3897/natureconservation.42.54735
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Betula halophila, a wild plant with extremely small populations, is endemic to Xinjiang, northwest China. Its wild populations have declined severely in the field. Understanding the patterns of floristic composition where congeneric species of B. halophila are distributed and their determinants is a necessary step to restore the wild populations. Based on literature records, specimen information, shared public data and field survey data, the patterns of floristic composition, diversity and environmental conditions of seed flora within the distribution areas of five native species (i.e. B. tianschanica, B. microphylla, B. pendula, B. rotundifolia and B. humilis), congeneric with B. halophila, were examined. The results are as follows. (1) There were 3013 species, 693 genera and 108 families of seed plants in the distribution area of these congeneric species of B. halophila, which accounted for 86.16%, 94.54% and 93.91% of the total seed plants in Xinjiang, respectively. (2) The family composition of seed flora in the distribution area of these congeneric species of B. halophila was mainly cosmopolitan; the genus composition of seed flora was dominated by temperate, mainly of northern temperate and Mediterranean components. (3) There are no significant differences existing in plant richness amongst the areas where each of the five congeneric species (B. tianschanica, B. microphylla, B. pendula, B. rotundifolia and B. humilis) are distributed. (4) The influence of climate factors on species richness is significant across the whole distribution areas of the Betula genus, while the main environmental factors determining species richness are different amongst distribution areas of different species. Climate factors impacted significantly on species richness in distribution areas of tree species, but not in distribution areas of shrub species. This study provides a preliminary guideline for the conservation of B. halophila, a wild plant with extremely small populations in the field.
Betula, congeneric species, geographic elements, richness, wild plant with extremely small populations
Betula halophila, a deciduous shrub species in the genus Betula of the family Betulaceae, is an endangered and salt-tolerant plant, which is distributed only in Xinjiang in northwest China. In 1999, the species is firstly listed as one of the key protected wild plants of China with a second-class protection level (State Forestry Administration and Ministry of Agriculture 1999). In 2011, the species was listed as one of the 120 wild plants with extremely small populations in China (
Betula genus, belonging to Betulaceae, plays an important role in the flora and vegetation composition of Xinjiang. Betula is an essential part of the typical mountain broad-leaved forest in Xinjiang. There is a close relationship between the small leaf broad-leaved forest and the typical mountain coniferous forest in Xinjiang. Betula genera in Xinjiang include six species (B. tianschanica, B. microphylla B. pendula, B. rotundifolia, B. humilis and B. halophila) (
Researchers have done a lot of research on all species of Betula native in Xinjiang. These works are mainly related to taxonomy, phylogeny and physiology. The systematic classification of Betula in Xinjiang has always been controversial (
The formation of flora is a comprehensive reflection of the evolution and temporal and spatial distribution of the flora in a certain natural historical environment. The flora of a specific region not only reflects the causal relationship between the total plants and the environment in the region, but also reflects the evolution of the flora in the geological history (
Arid regions account for 38–41% of the global land area. Compared with other regions and ecosystems, arid ecosystems are very sensitive to climate change and human activities (
B. halophila is a typical wild plant with extremely small populations, which can provide important genetic resources for the cultivation of salt resistant varieties. However, the wild population of this species has not been found for more than ten years. In order to rescue and restore the populations of this species, the most important is to ensure the preservation of this genetic resource as early as possible. In order to expand the existing population size of this species as much as possible, we hope to expand the population number by adopting the way of near natural re-introduction of seedlings, so as to provide a rational basis for fast restoration of the populations. Based on the distribution data of congeneric species of B. halophila, we compared the floristic and diversity characteristics of floras within distribution areas of these species and assessed the main factors affecting the diversity patterns of their floras of these congeneric species of B. halophila in Xinjiang. We hope our study can provide a scientific guideline for the conservation of B. halophila, a wild plant with extremely small populations.
Xinjiang is located in the hinterland of Eurasia (34°25'~ 49°10'N, 73°40'~ 96°18'E), with a total area of about 1.6×106 km2, accounting for about one sixth of China’s total land area and is the largest provincial administrative unit in China. Xinjiang has a complex terrain with a typical geomorphic pattern of “three mountains and two basins”. From north to south, these are Altai Mountains, Junggar Basin, Tianshan Mountains, Tarim Basin and Kunlun Mountains (
Based on a large number of herbarium specimens (http://www.cvh.org.cn/), a list of Chinese seed plant species and distribution information at provincial level (
Geographic distribution of congeneric species with Betula halophila, flora regions and main geomorphology in Xinjiang, northwest China a geographic distribution of B. tianschanica b geographic distribution of B. microphylla c geographic distribution of B. pendula d geographic distribution of B. rotundifolia e geographic distribution of B. humilis f geographic distribution of five species of Betula genus in Xinjiang g geographic distribution of flora regions, IA2 Altai Region, IA3 Tianshan Region, IIC5 Junggar Region, IIC6 Kashgar Region, IIIF17 Tibet, Pamirs and Kunlun Region h geographic distribution of main geomorphology.
In this study, species richness (S) was used to indicate species diversity. In order to compare the species composition of different flora and different species distribution areas, the Sørensen similarity coefficient of species composition in different flora areas was calculated (
Across all the distribution areas of the five congeneric species of B. halophila, there are 3013 species of seed plants, belonging to 693 genera and 108 families. There are 33 species of gymnosperms and 2980 species of angiosperms. Amongst the 108 families, there are 368 species of Asteraceae, 283 species of Poaceae, 253 species of Fabaceae, 152 species of Rosaceae, 147 species of Ranunculaceae, 134 species of Lamiaceae, 128 species of Brassicaceae, 127 species of Chenopodiaceae, 114 species of Caryophyllaceae, 107 species of Apiaceae and 102 species of Liliaceae, all of which contain more than 100 species. Amongst the other families, 63 families contain less than 10 species. There are 22 families with only one species. Amongst the 693 genera, Astragulus has the most species, including 92 species, followed by Carex (60 species), Allium (56 species), Artemisia (53 species), Oxytropis (41 species), Ranunculus (41 species) and Saussurea (40 species). In addition, there is only one species in 307 genera.
There are 108 families of seed plants in the distribution area of congeneric species of B. halophila. The proportions of the cosmopolitan, temperate and tropical (
Statistics of geographic elements for families and genera in distribution areas for congeneric species with Betula halophila in Xinjiang, northwest China.
Geographic elements | Number of families | Percentage of total families (%) | Number of genera | Percentage of total genera (%) | |
---|---|---|---|---|---|
Major types | Types | ||||
Cosmopolitan | Cosmopolitan | 50 | 46.30 | 72 | 10.39 |
Tropical | Tropical Asia- Australia and Tropical America | 21 | 19.44 | 42 | 6.06 |
Tropical and Subtropical East Asia & (South) Tropical America disjuncted | 3 | 2.78 | 5 | 0.72 | |
Old World Tropics | / | / | 8 | 1.15 | |
Tropical Asia to Tropical Australia | / | / | 4 | 0.58 | |
Tropical Asia to Tropical Africa | / | / | 3 | 0.43 | |
Tropical Asia | / | / | 6 | 0.87 | |
Temperate | North Temperate | 26 | 24.07 | 228 | 32.90 |
East Asia & North America disjuncted | 1 | 0.93 | 17 | 2.45 | |
Old World Temperate | 4 | 3.70 | 120 | 17.32 | |
Temperate Asia | / | / | 25 | 3.61 | |
Mediterranean, western Asia to central Asia | 2 | 1.85 | 77 | 11.11 | |
Central Asia | 1 | 0.93 | 62 | 8.95 | |
East Asia | / | / | 15 | 2.16 | |
Endemic to China | / | / | 9 | 1.30 |
The proportions of the cosmopolitan, temperate and tropical families are similar within all five species distribution areas and the proportion of the cosmopolitan family is dominant (Fig.
Percentage of geographic elements of compositions of different distribution areas for congeneric species with Betula halophila a family in different distribution areas for congeneric species with B. halophila b genus in different distribution areas for congeneric species with B. halophila (TSH: B. tianschanica; XYH: B. microphylla; CZH: B. pendula; YYH: B. rotundifolia; DSH: B. humilis) in Xinjiang, northwest China.
There was no significant difference in plant richness amongst the distributional areas of each of the five species congeneric with B. halophila, but there was a trend (Fig.
Comparisons of mean plant richness of different distribution areas for congeneric species of Betula halophila based on the spatial unit of 50 km × 50 km a number of families in different distribution areas for congeneric species with B. halophila b number of genera in different distribution areas for congeneric species with B. halophila c number of species in different distribution areas for congeneric species with B. halophila)(TSH: B. tianschanica; XYH: B. microphylla; CZH: B. pendula; YYH: B. rotundifolia; DSH: B. humilis) in Xinjiang, northwest China.
Sørenson similarity coefficients of compositions in distribution areas of different species for congeneric species with Betula halophila in Xinjiang, northwest China.
B. tianschanica | B. microphylla | B. pendula | B. rotundifolia | B. humilis | |
---|---|---|---|---|---|
B. tianschanica | / | / | / | / | / |
B. microphylla | 1.04 | / | / | / | / |
B. pendula | 1.06 | 1.02 | / | / | / |
B. rotundifolia | 1.35 | 1.39 | 1.40 | / | / |
B. humilis | 1.32 | 1.36 | 1.37 | 1.03 | / |
The species richness in the distribution areas of the five congeneric species of B. halophila varied not significantly with the increase in longitude (R2 = 0.00, P > 0.05), but significantly increased with the increase in latitude (R2 = 0.27, P < 0.01) (Fig.
Correlations (R2) between the species richness in species distribution areas of congeneric species with Betula halophila and their main environmental factors in Xinjiang, northwest China.
Species | Longitude | Latitude | Altitude | Mean annual temperature | Mean annual precipitation | Mean annual evapotranspiration |
---|---|---|---|---|---|---|
B. tianschanica | 0.26* | 0.23* | -0.01 | 0.03* | 0.11* | 0.14* |
B. microphylla | 0.11* | 0.22* | -0.01 | 0.04* | 0.14* | 0.16* |
B. pendula | 0.07* | 0.19* | -0.00 | 0.01* | 0.09* | 0.12* |
B. rotundifolia | 0.23* | 0.01 | 0.07 | 0.00 | -0.11 | -0.11 |
B. humilis | -0.00 | 0.02 | -0.08 | -0.07 | -0.08 | -0.11 |
In the distribution area with Betula species, there are 3013 species, 693 genera and 108 families of seed plants, accounting for 86.16%, 94.54% and 93.91%, respectively, of the total seed plants in Xinjiang (
According to the records of Flora Xinjiangensis (Editorial Committee of Flora Xinjiangensis 1992–2011), all species of congeneric species of B. halophila are mainly distributed in the Altai mountain area in Xinjiang, except for B. tianschanica which is mainly located in Tianshan Mountains. Amongst those four species mainly distributed in Altai, B. pendula and B. microphylla are also partly present in the western mountain areas of Junggar Basin. In Xinjiang, mountain coniferous forest is the main forest vegetation type, followed by mountain broad-leaved forest. The latter is closely related to the former. Amongst the mountain broad-leaved forests in Xinjiang, the small-leaved forest, composed of poplar and birch, is especially typical forest (
There are significant differences in plant richness amongst seed plant floras in the distribution area of congeneric species of B. halophila. The plant abundances of different life forms of these congeneric species are obviously different, while those of common life forms of these species are not significantly different. Latitude and climate have a significant influence on species richness in the distribution areas of congeneric species of B. halophila. It has been thought that latitude is actually a comprehensive factor. Therefore, we tend to think that climate is the key factor impacting on the distribution pattern of species diversity in the distribution areas of congeneric species of B. halophila, which also conforms to the view that climate plays a key role in species diversity in Xinjiang (
Wild populations of B. halophila have not been found in the field since 2003. The biological characteristics of the species need to be further understood in order to realise its effective protection and return in the wild. Due to the lack of wild population, the understanding of its ecological characteristics is very limited. Our study will help to strengthen the understanding of this species through the analysis of species composition, floristic characteristics and species diversity of the native congeneric of this species. From the point of view of phylogeny, it is necessary to carry out an in-depth study combined with the phylogeny of this species. From the current research, the phylogenetic relationship between this species and other related species is not clear. The clear phylogenetic relationship of this species is helpful to reveal the origin of this species and provide an important traceability basis for its protection. In terms of floristic composition, the cosmopolitan families and temperate genera are dominant in the distribution area of B. halophila. The climate niche of the species in the wild is consistent with that of Betula genus. It seems that niche simulation can be used to simulate the potentially suitable distribution area of B. halophila, which provides an important basis for the selection of the wild return to a great extent. Therefore, the current optimum distribution area of Betula genus in Xinjiang is the preferred geographical region for wild return of B. halophila when the primary wild habitat of B. halophila is not suitable for its survival at local scale any more. From this study, we also found that there are obvious differences in the factors affecting the species distribution at the local scale and in different distribution areas of related species. Therefore, more factors should be considered in the follow-up and the community level investigation work should be carried out in order to provide an important ecological reference for the wild return of B. halophila.
Thanks to Dr. Liping Li, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, for providing some survey data. Thanks to Dr. Cheng Wang, Forestry College, Shandong Agricultural University for sharing progress and opinions of Betulaceae phylogeny. Thanks to Chunjiang Li, Beitun Forest Farm, Altay, Xinjiang for his assistance in the field survey. We are particularly grateful to the editors and reviewers for their valuable comments on the manuscript.
This work was supported by the National Key Research and Development Program Project [grant numbers: 2016YFC0503103]; and the Fundamental Research Funds for the Central Non-profit Research Institution of Chinese Academy of Forestry [grant number: CAFYBB2019ZA002, CAFYBB2014MA005].
Figure S1. The correlation between environmental variables in distribution areas of five congeneric species with Betula halophila
Data type: Generating graph based on measurement and occurrence data.
Explanation note: The correlation between longitude (Long), latitude (Lati), altitude (Alti), mean annual temperature (Tem), mean annual precipitation (Pre) and evapotranspiration (Et) in distribution areas of five congeneric species with Betula halophila. (a) TSH: B. tianschanica; (b) XYH: B. microphylla; (c) CZH: B. pendula; (d) YYH: B. rotundifolia; (e) DSH: B. humilis).
Figure S2. The distribution frequency of Betula species varies with the environment gradients
Data type: Generating graph based on measurement and occurrence data.
Explanation note: The distribution frequency of Betula species varies with the environment gradients and the environmental variable values of Betula halophila were once distributed in the field.