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Riparian Areas: Rivers and Wetlands

Anna’s hummingbird along the San Pedro River Corridor

Riparian corridors are important routes for hundreds of species of migratory birds and home to many more, such as this Anna’s hummingbird along the San Pedro River Corridor. Identify birds you see with the Bird Finder by Ask A Biologist.

Riparian areas are dramatic elements of the Arizona landscape. Dependent on water, they are often easily spotted as vibrant greens and full vegetation that stand out against dry grasses and scrub trees.

Water, soil, and vegetation determine a riparian zone. Water is the most limiting factor to the survival of wildlife and plants. Trees and grasses grow faster, bigger, and with more variety in wet areas. Stands of cottonwood, willow, alders, or flourishing mesquite bosques are good clues to the presence of a riparian zone, even if there is no water present.

Riparian areas, particularly river systems, are called “ribbons of life,” appropriate because their ecosystems can extend through desert, grasslands, and other biotic communities. Large patches of desert thwart most nomadic animals. These areas link the uplands of southeastern Arizona's Sky Islands to the desert lowlands, providing essential migration routes for birds, and creating corridors so species are not stranded and isolated from other populations.

Riparian areas are the most productive habitats in North America. In fact, seventy percent of Arizona’s threatened and endangered vertebrates depend on them. (Use the Arizona HabiMap to view all of Arizona’s riparian systems and look at species distribution.) These zones host resident and migrating birds, including many of Arizona’s eighteen species of hummingbirds. They are considered “critical areas” to the health of the desert and to wildlife diversity in the southwest. 

Wet or Dry

Riparian areas make up only about 2% of the land in the Western U.S. and only 0.4% of arid Arizona. The natural water cycle in riparian areas improves the quality and sustainability of the land. Riparian soils have higher moisture content and are considered “young” soils because they are eroded and moved around by floods. Soil movement rejuvenates floodplains. Rivers capture water from monsoon storms and store it for later use. A healthy riparian system channels and distributes floodwater, stabilizes stream banks, and recharges surface aquifers through the slow absorption of water back into the ground. These water systems also refine sediments and transfer nutrients from the uplands to the desert lowlands, improving soil quality and increasing the land’s carrying capacity for farmed crops and livestock. This natural refinement system can even decrease pollutant levels.Some experts believe that for an area to be “riparian” it must be adjacent to a perennial (year round) or intermittent (most of the year) water source. But a whopping 90% of Arizona’s streams are ephemeral, products of seasonal rains. These sources blossom with life in the wet season and vanish after the rains end. Though brief, their presence gives the opportunity for abundant growth where otherwise there would be very little. Others are perennially fed from snowmelt, yet go dry during the year due to a sinking water table.