The relationship between water-level fluctuation factors and the distribution of <i>Carex</i> in floodplain grassland around Poyang Lake

Abstract

水位波动对鄱阳湖草滩湿地的形成与分布至关重要，但不同要素对湿地植物种的具体影响不尽相同.本研究以湿地优势植被苔草群落为研究对象，通过环湖区样带设置和植被调查得到较大尺度上的苔草分布数据，以不同水文站水文数据结合湖区DEM插值得出各样点水位波动要素数据：年内最大水位差R，年内淹没出露频次F，年平均水位M，最长淹没的出露日期D，年内总出露时间T，用CART模型进行分析.结果表明：1）影响鄱阳湖区草滩湿地苔草群落分布的最直接的水位波动要素为T和R；2）年内总出露时间大于84天（T ≥ 4.619），年极差水位大于11.3 m（R ≥ 10.41）时，苔草群落的综合分布情况最佳.进一步探讨认为：其他水位波动要素未能被CART模型选为分类依据，可能是因为彼此之间存在相关性；高程决定植被分布，实际上是多种水位波动要素综合影响的结果，精度要求不高时，可以用高程替代水位波动各要素进行简略分析.本研究相关结论可以为鄱阳湖控湖工程今后的运行，提供一定的参考，以维持草滩湿地生态系统的稳定，更好地实现其生态价值.;Water-level fluctuations are very important to the formation and distribution of the floodplain grassland around Lake Poyang, and different factors of water-level fluctuations (aspects of water regime) have different effects on wetland plant species. In this study, we used CART model to analyze the relationship between the distribution of Carex and five water-level fluctuations factors (annual water level range,R;annual frequency,F;annual mean water level,M;date of emergency after the longest inundation,D;annual total dewatered time,T), with plant data from sampling around Poyang Lake and water regime date offered by local hydrology bureau. The results showed that:1) the main influence factors of the distribution of Carex were T and R;2) the optimum condition to Carex community should be described as T ≥ 4.619 and R ≥ 10.41,which means annual total dewatered time more than 84 days and annual water level range larger than 11.3 meters. Further discussion indicated that we can use dimension reduction methods in analyzing the effects of water level fluctuations on wetland vegetation in Poyang Lake, because of the inner correlation between the above mentioned five factors. Meanwhile, previously extensive application of elevation in this field is mainly due to the comprehensive influence of different water level fluctuation factors, and only should be used in conditions with low accuracy requirement. This study provided quantitative evidence that water-level fluctuation factors drive the distribution of Carex, and may assist in making decision regarding the dam management, for the purpose of maintaining the floodplain grassland ecosystem, as well as realizing its ecological value.