长江中下游生态护坡坡面植被分布特征

基于防洪、安全、生态等方面的考虑，长江中下游航道整治工程中大多数采用生态护坡结构，达到了稳定航道兼顾生态保护的目的，但工程运行后期的坡面植被并没有呈现出预想状态。为探究施工后的坡面植被分布特征及其成因，于2019年5月（洪水来临前）和10月（洪水淹没后）开展了2次系统调查，设置9个生态护坡样地，每个样地内按坡面高程划分3个高程区域（护坡下缘、中间高程、护坡上缘）。结果表明，坡面植被多呈斑块化，尤其是生态护坡下缘区域。共调查到维管束植物77种，其中禾本科、菊科、豆科植物种类数较多。植物群落以草本植物为主，一年生草本植物和多年生草本植物种类数相近，分别为35种和32种。不同高程区域，生态护坡植被种类差异明显，生态护坡下缘区域，以双穗雀稗、蒌蒿、水蓼等为主，生态护坡上缘区域以芦苇、狗牙根、牛鞭草等为主。洪水淹没前后植物优势度发生了很大变化。洪水淹没后，低高程区域植被覆盖度下降明显，很多样地优势种尤其是一年生草本植物优势度下降或消失。生态护坡工程是否成功，如何筛选植物和滞留土壤是关键。建议优先选用狗牙根、牛鞭草、双穗雀稗和芦苇等既耐水淹且根系发达的植物。与生态护坡砖型护坡相比，钢丝网格型护坡缝隙复杂、数量多、微生境复杂度更高。

Vegetation Distribution on the Ecological Protection Slopes of the Middle and Lower Yangtze River

Based on consideration of flood control, safety and ecosystem conservation, ecological slope protection structures were adopted for most waterway regulation projects in the middle and lower reaches of Yangtze River. However, the vegetation community did not develop to the extent expected in most ecological slope protection projects. The aim of this study was to characterize the distribution and formation mechanisms of the vegetation community on ecological protection slopes and provide a reference for improving their design to increase effectiveness. Systematic vegetation surveys were carried out on nine plots with different ecological slope protection structures in May (before flood season) and October (after flood season) of 2019. Each plot was divided into three areas by elevation (slope toe, middle and upper edge of the ecological protection slope). Plant species, height, coverage and biomass were recorded for each plot. Results show that the slope vegetation community was patchy, especially in the lower edge area. A total of 77 vascular plant species from 67 genera and 28 families were recorded, with dominance by Gramineae (15 species), Compositae (11 species) and Leguminosae (6 species). The plant communities were dominated by herbaceous plants, including 36 annuals and 34 perennials, and the dominant species clearly varied with elevation. Dominant species on the lower edges of the ecological protection slopes included Paspalum bicornatum, Artemisia selengensis and Polygonum hydropipectus, while reeds, bermuda grass and bullwhip dominated the upper slope areas. Plant dominance also changed markedly before and after flooding. Vegetation coverage, especially in low elevation areas, clearly decreased after inundation. The extent of species dominance, especially the annual herbaceous plants, decreased significantly and some species simply disappeared. The success of ecological slope protection depends primarily on plant selection and soil retention. We recommend selecting plants with strong resistance to high water and a well-developed root system, such as Bermuda grass, whip weed, Dallas grass and reeds. With regard to the soil retaining substrate that is constructed on ecological slope protection projects, steel wire mesh provides more gap and microenvironment complexity than stone or concrete.