Three riparian ecosystems, delineated by elevation, are recognized in
the arid and semi-arid southwestern United States and northern Mexico.
Riparian vegetation that occurs along the flood plain of stream channels
are typically composed of herbaceous species of Carex, Eleocharis, Juncus, and Scirpus and produce the characteristic dark
green edge along the channel systems. Woody plants, including saltcedar
(Tamarix pentandra), sycamore (Platanus wrightii), and cottonwood
(Populus fremontii), that are often associated with riparian ecosystems
are typically found higher up on the terraces next to the flood plains.
Elevation Makes a Difference
Above 7,000 ft, herbaceous species of sedges (Carex), rushes (Juncus),
spikerushes (Eleocharis), and bulrushes (Scirpus) predominate
along the edge of the stream channels. Willow, chokecherry (Prunus
virens), boxelder (Acer negundo), Rocky Mountain maple (A.
glabrum), and various coniferous tree species occupy the higher terraces.
Riparian ecosystems between 3,500 and 7,000 ft contain the greatest number
of plant species and the greatest canopy cover. Besides the characteristic
herbaceous plants along the flood plain, cottonwood, willow (Salix spp.), sycamore, ash (Fraxinusvelutina), and walnut (Juglans
major) are typically found on the terraces, with 3 or 4 species often
In ecosystems below 3,500 ft, many of the ephemeral streams have broad
alluvial floodplains that can support herbaceous plants and terraced bottoms
that often support high densities of deep-rooted trees including saltcedar,
sycamore, cottonwood, palo verdes (Cercidium spp.), and other species.
Water Scarcity is Relative
Because of the abundance of water, plants, and animals, riparian areas
provide valuable recreation opportunities as well as forage for livestock
and wildlife in an otherwise arid environment. Riparian ecosystems are
prime habitats for many game and non-game species of wildlife and fish.
Collectively, climatic characteristics of riparian ecosystems exhibit
a wide range of conditions due to large elevational differences and distributions
of associated mountain ranges and highlands. The key characteristic of
the riparian system is the availability of water throughout the year or
at least during the growing season.
Soils at the higher elevations generally consist of consolidated or unconsolidated
alluvial sediments from parent materials of the surrounding uplands. Soil
depths vary in riparian ecosystems, depending upon the stream gradient,
topographic setting, and parent materials. Soils on the flood plains at
lower elevations consist of recent depositions, tend to be uniform within
horizontal strata, and exhibit little development. The alluvial soils
in all ecosystems are subject to frequent flooding and, as a consequence,
are characterized by a range of textures. Riparian ecosystems vary from
narrow, deep, steep-walled canyon bottoms, to intermediately exposed sites
with at least one terrace or bench, to exposed, wide valleys with meandering
There are over 400 images available in the image
database illustrating various aspects and conditions found in chaparral
ecosystems in southwestern United States. These can be accessed
after getting into the database by using the key word riparian.
Additional key words are available for searching the images in a drop
down list within the database.
Riparian Ecosystems: General Information | Climate
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