Receding Water Line and Interspecific Competition Determines Plant Community Composition and Diversity in Wetlands in Beijing

Climate and human-induced wetland degradation has accelerated in recent years, not only resulting in reduced ecosystem services but also greatly affecting the composition and diversity of wetland plant communities. To date, the knowledge of the differences in community parameters and their successional trends in degraded wetlands remains scarce. Here based on remote sensing images, geographic information system technology, and statistical methods, we produced a successional gradient map of the Yeyahu Wetland Nature Reserve in Beijing, which has experienced a steady decline in water level in recent decades. In addition, we analyzed community composition and diversity along with each identified gradient. The results showed that community diversity decreases while dominance increases with the progress of succession, with the highest diversity occurring during the early stage of succession. Moreover, the community demonstrates greater similarity among subareas during later successional stages, and the similarity coefficients calculated from the important value (IV) of each species are more accurate. Correlation analysis showed that the impact of soil factors on diversity was not significant at a subarea scale, although these nutrients showed an increasing trend with the community succession. Furthermore, the IVs of the dominant species had a particularly significant impact on diversity, showing a significantly negative correlation with diversity indices and a significantly positive correlation with dominance indices. Further analysis showed that the retreat of water level resulted from sustained drought and local human activities was a major extrinsic driving force resulting in observed differences in the community successional stages, which resulted in differences in community composition and diversity. On the other hand, interspecific competition was the main intrinsic mechanism, which significantly influenced the IVs of the dominant species and community diversity. The results of this study could aid in improving the understanding of community composition, diversity, and its successional trends in degraded wetlands.

近年来，气候与人类活动共同驱动的湿地退化进程持续加快，不仅导致生态系统服务功能减退，更对湿地植物群落的组成与多样性造成显著影响。截至目前，学界对于退化湿地群落参数差异及其演替趋势的认知仍较为匮乏。本研究基于遥感影像（Remote Sensing Image）、地理信息系统（Geographic Information System, GIS）技术与统计学方法，针对近数十年来水位持续下降的北京野鸭湖湿地自然保护区，绘制了其湿地群落演替梯度图。此外，本研究针对各演替梯度开展了群落组成与多样性分析。研究结果显示，随着演替推进，群落多样性逐渐降低而优势度不断升高，且多样性峰值出现在演替早期阶段。此外，演替后期各亚区的群落相似性更高，且基于各物种重要值（Important Value, IV）计算得到的相似性系数结果更为准确。相关性分析结果表明，尽管土壤养分随群落演替呈上升趋势，但在亚区尺度上，土壤因子对群落多样性的影响并不显著。进一步分析显示，优势物种的重要值对群落多样性具有极为显著的影响：其与多样性指数呈显著负相关，而与优势度指数呈显著正相关。进一步研究发现，由持续干旱与当地人类活动共同导致的水位退缩，是引发群落演替阶段差异的主要外在驱动因子，而该差异进而造成了群落组成与多样性的分化。另一方面，种间竞争则是主导该过程的内在机制，其对优势物种重要值与群落多样性均具有显著影响。本研究结果有助于深化学界对退化湿地群落组成、多样性及其演替趋势的认知。