The black cottonwood, so named because the bark turns black as it ages and the seeds are covered with white cotton-like fluff, can form extensive groves with trees up to forty meters high when they reach maturity. Broken tops and limbs provide ideal shelter for birds and small mammals. The large horizontal branches provide excellent nesting sites for a variety of raptors and herons. These trees also provide stabilization for stream banks and cover to shade and cool the water. Fallen insects and leaves feed and fertilize the river and its inhabitants.
Uprooted trees slow the stream down and create pools.