The understory is silverberry. Cottonwood trees are found throughout the western United States and are important to riparian ecosystems. They tend to grow close to the water, providing shade that cools the water to temperatures required by native fish. Tree limbs and dead trees provide protective habitat areas for young fish. Cottonwood trees evolved on dynamic river systems that flood periodically.
Floods tear down riverbanks and carry sediment downstream to form new gravel bars.
Cottonwood seeds need this fresh gravel, which provides a moist, sunny environment on which to grow. New cottonwoods grow in new areas with fresh gravel bars, while old cottonwoods are replaced by juniper and sagebrush. Cottonwood forests are therefore part of a dynamic ecosystem dependent on natural flooding. The Idaho floods in 1996, however, provided a tremendous volume of water that created large gravel bars on which cottonwood seedlings could sprout. Now, hundreds of seedlings are thriving, ensuring healthy cottonwood populations in the area for years to come.