Lower on the floodplain, the mixed riparian forests become dominated by willows as the frequency and duration of flooding increases. At this boundary, adjacent to the channel, Willow Scrub communities are formed. The willow scrub communities are composed of the young, newly established willows and cottonwoods that can survive the frequent physical battering and inundation from flooding. Sandbar willows (Salix exigua) are common in these communities, especially on point bars. The presence of these willows allows finer sediments to accumulate, allowing additional riparian plants to establish.
Willow scrub communities are frequently described as early successional habitats, because these are the first plant communities to form on newly established point bars along rivers. The dense structure formed by young, multi-stemmed willows is the preferred nesting and cover habitat for many songbirds. This dense young plant community is also important browsing and foraging habitat for many riparian wildlife species and a good source of insects.
The structural complexity of mixed riparian forests, along with the size and diversity of plants, may explain why these forests attract such a great diversity of wildlife. These forests are particularly important to migratory birds. Multiple fruit bearing plants like blackberry, elderberry, rose and grape are a good food source for fledgling birds but also mammals, reptiles and invertebrates. The dense cover at multiple heights allows wildlife to build nests on the ground or in trees. Such cover also provides refuge during migration or dispersal.
For more information about Riparian Plant Communities see Conard and others 1977, Gaines 1980, Holstein 1984, Holland 1986, and CWHR 1988.