Distribution and succession of plant communities in Lake Bita coastal swamp on the plateau region, northwestern Yunnan

滇西北高原碧塔海湖滨带狭长型沟谷和宽广型沟谷设置了两条沼泽研究样带,研究了沼泽群落种类组成特征、群落分布与演替规律及其驱动因素。结果表明:两条样带总计调查到43种植物,隶属21科35属;群落中均以稀有种占多数,但总体上狭长型沟谷沼泽群落的均匀程度高于宽广型沟谷;α多样性各指数与沼泽水位均呈显著正相关,但β多样性与沼泽水位无相关性;沿水分梯度,沼泽群落呈现出挺水植物群落→沼泽植物群落→沼泽化草甸植物群落的生态序列分布,但是也在局部微地形作用下形成群落复合体;生态序列分布与湖岸特点和沟谷类型有关:狭长型沟谷具有陡坡湖岸,沼泽群落倾向于间断分布,宽广型沟谷具有缓坡湖岸,沼泽群落倾向于连续分布。以水分因子为主、以地形等因子为辅的综合环境因素是决定碧塔海湖滨沼泽群落植物多样性和生态序列分布格局的驱动因素,相应地植物群落演替特点为渐变式演替和跳跃式演替两种模式并存,但演替方向一致。;The plateau of northwestern Yunnan is the most typical distribution region of plateau swamp developed on Karst landform in China. The Lake Bita coastal swamp listed as Wetlands of International Importance under the Ramsar Agreement is a typical representative in the region. Vegetation succession and its driving forces of coastal swamp are the key scientific issues related to theoretical research on swamp in the distinctive region. In the present study, two transects across coastal swamp were set up and sampled in narrow valley and broad valley in the coastal zone of Lake Bita respectively. The environment characteristics and species composition of swamp vegetation were surveyed. Pearson correlation test and Detrended Correspondence Analysis (DCA) were applied to analyze the relationship between species composition and surface water level, the distribution and succession and associated driving forces of swamp vegetation. Some important findings were revealed. Twenty-one families, 35 genera, and 43 plant species were recorded along the two sampling transects. The highest number of species in family was observed in Cyperaceae and Ranunculaceae, each family contained six species and occupied 3.95% in total species of the vegetation community respectively, followed by Gentianaceae, which contained five species and hold sum total 11.63%. The highest number of species in genera were observed in Carex, Gentiana and Potamogeon, each genera contained three species, the second was Polygonum, it contained two species. At the transect scale, 16 families, 25 genera, and 28 species were recorded in the narrow valley transect, and 20 families, 31 genera, and 37 species were recorded in the broad valley transect. L- shaped and U-shaped patterns of frequency distribution based on plant species were presented in the narrow valley transect and broad valley transect respectively. The swamp community also comprised some rare species (only occurred in one or two quadrats) in the two transects. Among them, 11 and 10 rare species were observed in the narrow valley transect and broad valley transect separately, which accounted for 39.29% and 27.07%, respectively. The number of species occurred in two, three, five and fourteen quadrats in the broad valley transect was higher than that in the narrow valley transect. Species richness per quadrate and the total number of species showed similar patterns along the two transects and both showed significant correlation with surface water level, but Whittaker's index did not. Along the two sampling transects the distribution of plant community mainly presented in the following ecological series of emerged hydrophytic communit→ swamp community→ swampy meadow community under the impact of surface water level and supplemented with community complexity under the impact of local microtopography. The distribution patterns of plant community in two transects depended on the lakeshore types and valley topography. In the narrow valley with steep shore, the plant community presented discontinuous distribution, whereas in the broad valley with gradual shore, the plant community showed continuous distribution. The distribution patterns and species composition represented by Lake Bita swamp community were dominated by multiple environmental factors characterized by surface water level and microtopography in the plateau region of Northwestern Yunnan. Correspondingly, there existed continuous succession mode and saltatory succession mode in the process of plant community succession, but the two modes were identical in succession direction.