1. In wetlands, hydrochory is one of the main mechanisms of seed dispersal and there is often synchrony between propagule production and the flood season. Different sources of disturbance can prevent seed dispersal to suitable sites, and if environmental conditions are not adequate for germination and seedling establishment, recruitment will be limited, affecting succession.
2. We worked in a disturbed tropical freshwater swamp where the native grass Leersia hexandra has dominated open areas, creating a grass matrix that surrounds patches of swamp forest. Leersia grows vigorously, forming cushions of dry matter that cover the soil, forming a potential obstacle to seed dispersal. We asked whether the vegetative growth of this grass prevents the entry and dispersal of seeds of the tropical swamp tree Pachira aquatica, thwarting seed germination and seedling establishment, and arresting succession. We set up transects in the grass matrix in two zones: close to the river (R) and bordering the tree patches or fragments (F). We quantified tree seed and seedling presence, survival and growth in situ and experimentally introduced seeds and seedlings in the field and monitored seed germination and the survival and growth of their seedlings, as well as that of transplanted seedlings.
3. There was a negative relationship between the number of seeds and established seedlings, and the distance to river or fragment (r = −0.86, p < 0.001 for zone R; and r = −0.77, p < 0.001 for zone F) and with the grass cushion (r = −0.68, p = 0.005 for zone R; and r = −0.66, p = 0.007 for zone F); the grass creating a barrier to dispersal. When seeds were sown after clearing the grass cushion, germination success was high, so this stage is not limited. The transplanted seedlings had better survival and a greater final height than the seedlings of the sown seeds. Grass cover had a negative effect on both types of seedlings. Seedling survival rates were inversely related to grass cover, showing that seedlings overgrown by grass had low survival rates. Flooding is a stress factor for seedlings and produced mortality, in addition to the effects of the grass.
4. Together, the field survey and the experiment show that succession is being arrested in two ways: (1) by limiting seed dispersal because the grass cushion slows the dispersal and penetration of seeds into the vegetation; and (2) by limiting seedling establishment because the grass competes for space and light. Our results show that even where the grass is native, slower growing, seed‐dependent species may struggle to compete and establish. If grass cover is increasing, these swamps are very vulnerable to a decrease in area because it is very difficult for them to regenerate naturally.

中文翻译：

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六合草草对水生Pachira幼苗的扩散，种子萌发和建立的影响

1. 在湿地中，水力紧缩是种子传播的主要机制之一，繁殖繁殖和洪水季节之间通常是同步的。不同的干扰源可以阻止种子散布到合适的位置，如果环境条件不足以促进发芽和幼苗生长，募集将受到限制，影响演替。
2. 我们在一个受干扰的热带淡水沼泽中工作，当地的草紫草（Leersia hexandra）占据了开阔地带，形成了包围沼泽森林的草丛。紫花草生长旺盛，形成覆盖土壤的干物质垫层，对种子传播形成潜在的障碍。我们询问了这种草的营养生长是否会阻止热带沼泽树Pachira aquatica种子的进入和扩散阻止种子发芽和幼苗生长，并阻止演替。我们在草矩阵中的两个区域中设置样条：靠近河流（R）和与树木斑块或碎片（F）接壤。我们对树木种子和幼苗的存在，原位存活和生长进行了量化，并通过实验引入了田间种子和幼苗，并监测了种子发芽及其幼苗以及移植幼苗的存活和生长。
3. 种子和已定苗的数量与与河流或碎片的距离之间存在负相关关系（R 区为r  = -0.86，p <0.001； F区为r  = -0.77，p <0.001），并且与草垫（R  = -0.68，p  = 0.005，区域R; r  = -0.66，p = F区的0.007）；草造成了传播障碍。清除草垫后播种时，发芽成功率很高，因此这个阶段不受限制。移植的幼苗比播种的种子具有更好的存活率和更高的最终高度。草被覆盖对两种类型的幼苗都有负面影响。幼苗成活率与草被成反比，表明草长满的幼苗成活率低。除了草的影响外，洪水是幼苗生长的压力因素，也是造成死亡的原因。
4. 总之，实地调查和实验表明，可以通过两种方式阻止演替：（1）通过限制种子散布，因为草垫减慢了种子散布和向植物中的渗透；（2）通过限制幼苗的生长，因为草竞争空间和光线。我们的结果表明，即使在草是本地植物的情况下，生长较慢，种子依赖的物种也可能难以竞争和建立。如果草皮增加，这些沼泽地极易受到面积减少的影响，因为它们很难自然再生。