Chapter 2: Characterization of Riparian Areas

Riparian Vegetation

The kinds and amounts of vegetation in the riparian areas are different than terrestrial vegetation. These differences reflect the influence of free or unbound water from the adjacent watercourse or water body.

Figure 2.7. The red line highlights the distinctive riparian vegetation.

 

  1. To identify the expected vegetation for riparian areas traditionally plants have categorized as obligate riparian, facultative and upland.
    • Obligate riparian species (also called phreatophytes) are found almost exclusively in riparian areas.
    • Facultative species are commonly found in the upland and riparian areas.
    • Finally upland species are rarely found in riparian areas.
  2. Detailed classification schemes provide percentages of the plant occurrence in riparian areas. Categories developed for major tree species are: 
    • obligate riparian (91-100%), Goodding’s willow (Salix gooddingii),
    • preferential riparian (76-90%), Fremont cottonwood (Populus fremontii) and Arizona walnut (Juglans major ),
    • facultative riparian (26-75%), velvet ash (Fraxinus velutina),
    • nonriparian (0-25%) netleaf hackberry (Celtis laevigata var. reticulata), Texas mulberry (Morus microphylla) and mesquite (Prosopis ssp.).
  3. Riparian vegetation has been also categorized in three broad ecosystems based on elevation for the southwesten United States.
    • Elevations less than 3280 ft and associated with perennial, intermittent and ephemeral streams and rivers with broad floodplains and terraced bottoms. These sites support deep rooted trees like saltcedar (Tamarix ssp.), Arizona sycamore, Fremont cottonwood and paloverde (Cercidium ssp.) and many herbaceous plants like sedges (Carex spp.), rushes (Juncus ssp.), spikerushes (Eleocharis ssp.), bulrushes (Scirpus ssp.).
    • The next category of ecosystems is between 3280-6560 ft with Fremont cottonwoods, willows, Arizona sycamore, velvet ash, and Arizona walnut. Several herbaceous plants are present in the understory. The vegetation covers narrow strips along primarily intermittent and ephemeral streams because very few perennial streams remain in these elevations. 
    • The last category is riparian ecosystems at elevations greater than 6560 ft. Characteristic woody species include willow, chokecherry (Prunus Virens), boxelder (Acer negundo), Rocky Mountain maple (Acer glabrum) and various conifers and herbaceous plants.  In areas of excessive soil perennial moisture wetlands and mountain meadows can be supported. 
  4. Riparian areas have extremely high plant diversity although they typically occupy small areas in the southwestern United States. In southeastern California, southern Arizona and central and southern New Mexico, 579 plants were categorized as obligate and preferential riparian species and 812 as facultative riparian species.

Woody and herbaceous species in riparian areas

 

    

Figure 2.8. Fremont Cottonwood.

 

 

   

Figure 2.9. Arizona Ash (left) and Desert Willow (right)

 

 

  

Figure 2.10. Gooding’s Willow.

 

 

Figure 2.11. Arizona Sycamore.

 

 

Figure 2.12. Arroyo Willow (left), Arrowweed (right).

 

 

Figure 2.13.Deer grass (left) and Cattail (right).