These lush areas are interesting because of periodic flooding.  Usually once a year (sometimes more) the rivers overrun their banks bringing water and silt onto the surrounding land.  Trees survive and grow well, fertilized by the river's silt, but herbaceous plants are fewer.  Some species do take hold, often vines and other thick growing plants and they can overtake the banks.  Walking through such overgrown areas can be difficult.  Common trees in this habitat include American Sycamore, Willows, Aspens, and Cottonwood.  Herbaceous plants vary depending on the region, but Wild Grape, Cucumber, and Virginia Creeper are among the vines found growing.  Poison Ivy grows readily in this habitat, itis most common in the southern tier.