Floodplain forests are forested wetlands found on alluvial flats and terraces of river valleys. They are best-developed on medium to large rivers and in such examples are often quite distinct from adjacent riparian forests, which form on slightly elevated natural levees immediately along the stream bank. Floodplain forests tend to form behind the riparian strip. They may appear to be relatively flat but often there are distinct microtopographical features such as small swales and ridges, hummocks, etc. In these areas differencs of a few centimeters can result in profound differences in duration and frequency of inundation or saturation.
Along some rivers, distinct low- and high-floodplain communities may exist. This is particularly true along large rivers. The low-floodplain communities are more frequently inundated and for longer periods of time and are usually positioned on first bottoms of the river floodplain. Second bottoms often support high-floodplainc communities and are more well-drained.