Introduced species and climate change can have direct impacts on wetland communities, but they can also produce indirect effects such that climate change (i.e., effects of flooding and salinity) can affect native plants by exacerbating or reducing invasion. We assessed the direct and indirect effects of flooding, salinity, and introduced species on wetland communities across a salinity gradient by analyzing existing monitoring data from over 390 Coastwide Reference and Monitoring Sites (CRMS) using path analysis. As expected, we found that introduced species cover and richness was highest in fresh marshes and decreased across the salinity gradient. In fresh marshes, introduced cover and salinity separately negatively affected native cover and richness, but there were no indirect effects. In intermediate marshes, introduced cover and salinity reduced native cover and richness, and indirect effects were weakly positive because salinity negatively affected introduced cover. In brackish and saline marshes increasing salinity and flooding reduced native cover and richness. Our results suggest that climate change will negatively affect all wetland plant communities, and invasion will negatively affect fresher wetlands; however, climate change will not exacerbate invasions in wetlands and could reduce introduced species effects.

引进的物种和气候变化可能对湿地社区产生直接影响，但它们也可能产生间接影响，例如气候变化（即洪水和盐碱化的影响）可以通过加剧或减少入侵来影响本土植物。通过使用路径分析分析了390多个沿海参考和监测站点（CRMS）的现有监测数据，我们评估了整个盐度梯度对洪水，盐分和引入物种对湿地社区的直接和间接影响。不出所料，我们发现引入的物种覆盖度和丰富度在新鲜沼泽中最高，而在整个盐度梯度上则下降。在新鲜的沼泽中，引入的覆盖率和盐度分别对本地覆盖率和丰富度产生负面影响，但没有间接影响。在中间的沼泽里 引入的掩盖度和盐度降低了原生的掩盖度和丰富度，间接影响弱于正值，因为盐度对引入的掩盖度产生负面影响。在咸淡水和盐碱沼泽中，盐分增加和洪水泛滥，减少了自然覆盖和丰富度。我们的结果表明，气候变化将对所有湿地植物群落产生负面影响，而入侵将对较新鲜的湿地产生负面影响。但是，气候变化不会加剧对湿地的入侵，并可以减少引入物种的影响。入侵将对较新的湿地产生负面影响；但是，气候变化不会加剧对湿地的入侵，并可以减少引入物种的影响。入侵将对较新的湿地产生负面影响；但是，气候变化不会加剧对湿地的入侵，并可以减少引入物种的影响。