The structural complexity of riparian vegetation has a big impact on wildlife abundance and community composition (what lives in an area). Many animals—like songbirds, deer, bald eagles, and black bear—require specific structural attributes—things like snags or dense shrub thickets or large living trees. The structural complexity of riparian plant communities provides many layers for foraging by different wildlife species. The variety of wildlife habitats is typically greatest in structurally diverse riparian habitats because they can support specialized as well as more generalist species. In addition to structural form, the species composition of riparian plant communities influences wildlife in riparian areas. This is especially true if there are differences in the food value of riparian versus upland vegetation, e.g. the presence of deciduous trees along streams in coniferous forests.

Complex riparian plant species often host different insect species than surrounding lands, further distinguishing their food value for everything from fish to birds to mammals. Insect eaters such as bats, shrews, flycatchers, swallows, and some salamanders, often forage preferentially in riparian areas because of increased insect abundance.

Predators (e.g., coyotes, martens, hawks, owls) are in turn attracted to the abundance of prey in riparian habitats. The absence of vegetation on sand and gravel bars due to continual erosion and deposition can provide nesting habitat for some species (e.g., belted kingfishers nest on steeply sloped streambanks; spotted sandpipers nest on sandy shoals) and resting habitat for other species (e.g., migrating birds and boreal toads rest on sandbars).

Complex riparian areas, with all their structural and compositional diversity also provide habitat for many wildlife species for breeding and rearing young. Many waterfowl and other birds nest on floating platforms, in trees or snags adjacent to or in streams and ponds. Fawning and calving grounds of ungulates are often near riparian areas because of the quality of food and cover.

Complexity also provides cover in close proximity to abundant food, which is critical. Waterfowl, for example, use sheltered areas at the edges of streams and ponds for hiding and resting cover. Many terrestrial vertebrate species use hollow logs and trees, cavities in logs and trees, and dense foliage in riparian areas for hiding and resting cover. The abundance of shrubs and trees in riparian areas provide safe perches for many bird species.

Bottom line is, when it comes to riparian areas complexity is vitally important for wildlife.

In general, floodplains are simplified when natural processes are simplified—for example when riparian and floodplain flows are curtailed or when fires are excluded. A natural stream will have flood cycles occurring on 10-20 year intervals. Historically, fires burned through riparian forests every 65-100 years and riparian shrub habitats every 25-50 years.

Humans also reduce complexity. A black cottonwood/ponderosa pine riparian forest might harbor some 50 native plant species (trees, shrubs, herbs, and grasses), but once it is converted to agricultural land it might have fewer than five species, all non-native. Floodplain areas once characterized by sloughs, brush piles, downed logs, and small areas of high ground have been cleared and graded flat, further reducing habitat complexity. Historically, beavers added to the river’s complexity by storing water and changing plant community structure. Reductions in their populations have further simplified habitats.

Major factors contributing to the decline in riparian areas and how they function include: excessive livestock grazing; timber harvesting; fire management; conversion to crop and pastureland; road development; dams, diversions, and/or pumping; and reductions of native wildlife populations like beaver. On rangelands, excessive livestock grazing pressure has been one of the most important factors harming riparian areas. On forested landscapes, logging practices (including fire suppression) and road building have had the greatest impacts on riparian areas. To a lesser extent, disturbances associated with recreational uses and residential development have also contributed to the decrease in riparian area complexity.