Chapter 6 Riparian Authors: Corrine Dolan and Alix Rogstad
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Chapter 6 Riparian Authors: Corrine Dolan and Alix Rogstad Cover photo: Courtesy of the “Living with Wildfire: Homeowners’ Firewise Guide for Arizona” tabloid published by The Arizona Interagency Coordinating Group. Chapter 6 74 RIPARIAN Description people, and domestic animals. Riparian vegetation communities are valued for high biodiversity, including insect and crustaceous species that are vital in the food web. In addition, riparian areas are treasured for recreational activities such as hiking, camping, fishing, rafting, and bird watching. Furthermore, riparian areas provide environmental services that are important for ecosystem function, including improved water quality and quantity as well as erosion control. Photo by Bill Boyett Riparian areas are dynamic and adapted to natural disturbances. Seasonal flooding is very important to Burro Creek the regeneration of the vegetation found in riparian Riparian (streamside) vegetation communities vary areas (Dwire and Kauffman 2003) because it reduces in structure and species composition, depending on or eliminates older, decadent vegetation and location. In general, riparian areas are transitional promotes newer, healthier plant establishment and zones between terrestrial and aquatic ecosystems. In growth. Floods serve to irrigate the surrounding other words, they are areas along a river or stream floodplain and wash away dead and dying litter with water-loving vegetation. Riparian vegetation and woody debris. Seasonal flooding also was communities can be found at all elevations and in important to Native American populations who each of the other vegetation communities described lived along the rivers of Arizona. Some tribes in this publication. To read more about riparian planted crops in the surrounding floodplain, using areas associated with other vegetation communities, the flooding events to irrigate and fertilize (Austin see the Special Case Boxes in Chapters 1 through and Wolf 2001). 3 of this publication. This chapter will focus on riparian areas at low elevations with flowing water at least part of the year. The riparian areas discussed in this chapter are different from neighboring vegetation formations because they are wetter, shadier, and contain different kinds of soils and plant species. Microclimates in riparian areas tend to be cooler with higher relative humidity when compared to adjacent vegetation communities (Dwire and Kauffman 2003). For the purposes of this discussion, riparian areas are considered to contain flowing water at least part of the year. There are approximately 93,000 linear miles (USGS 2004) of riparian vegetation communities (including streams, rivers, washes, canyons, wetlands) in Arizona (Figure 6.1). Box 6.1 describes types of riparian vegetation communities in Arizona and management concerns for each. The presence of water, lush green plants, and cooler Photo by Cori Dolan temperatures attract a diversity of wildlife species, Fall colors in the Ramsey Canyon Nature Preserve Chapter 6 75 Riparian Figure 6.1 Riparian Areas in Arizona Chapter 6 76 Box 6.1 Riparian Vegetation communities in Arizona* River Surrounding Location Fire Management Issues System Vegetation Recreation is the biggest human use of this area. The steady rise in the number of visitors has increased human-caused ignitions. Ground-water Sonoran Desert Scrub, pumping by humans has drawn down the water table creating drier conditions West Central including a significant that are more conducive to fire. Finally, the surrounding vegetation includes River Arizona nonnative species nonnative species such as red brome that increase fire frequency and size. component. Operations and releases from Alamo Dam are probably the biggest influence Bill Williams on this river. Most of the river is on a National Wildlife Refuge, BLM- administered wilderness, and a few private ranches. The Salt River extends through Forest, Woodland, Recreation has a large impact on the upper Gila, Gila Box Riparian Natural Southern and and Desert Scrub areas. Conservation Area (RNCA), and along the Gila River in the Winkelman area. Rivers Western Arizona The Gila River is mostly There is a high potential for human-caused ignitions in these areas. surrounded by Desert Salt and Gila Scrub in Arizona. This area is used for recreation by boaters and campers who increase ignitions along the river. A major cause of fires in this area is visitors setting fire to Russian thistle (tumbleweeds), a nonnative plant that carries and spreads fire Northwestern to other areas. To prevent nonnative plants from spreading, fire crews sanitize Mohave Desert Scrub River Arizona equipment before entering riparian areas. There is a buffer zone around the river where aerial retardant is prohibited to protect endangered fishes. Outside Upper Colorado this buffer zone, fires are suppressed by firefighters with hand tools or are allowed to burn out. A high priority in this area is the management of habitat for threatened and endangered species, many of which can be impacted by fire. In areas where salt cedar (Tamarix spp.) grows in large monotypic stands, fires exhibit extreme behavior that can threaten habitat and communities within the wildland-urban Western Arizona Sonoran Desert Scrub interface (WUI). Recreation is a significant activity on this river system and River increases possible ignition sources. Undocumented immigrants also increase ignitions in this area. Some prescribed fire is used to manage threaten and Lower Colorado endangered species habitat. Most commonly, mechanical treatments such as thinning are used along WUI areas to reduce wildland fire risk. Nonnative tamarisk (salt cedar) is not as much a problem along this river as Southeastern Grassland and Sonoran the others. Flood debris piles increase fuel loads within the cottonwood gallery Arizona Desert Scrub forest. Undocumented immigrants start fires along the San Pedro corridor. San Pedro River The biggest issue facing this system is the fact that the land bordering the river is private land. No agreement has been made among the landowners regarding a conservation plan for the area. The National Park Service is Southeastern Grassland and Sonoran constructing firebreaks near Tumacácori National Historical Park to reduce River Arizona Desert Scrub fuel loads in areas that border human communities. The nearby wastewater Santa Cruz treatment plant provides the stream flow to the Santa Cruz, increasing moisture content and decreasing the potential for a high-intensity fire. Therefore, fire management is a low priority in this area. *Fire Management Information courtesy of the Bureau of Land Management and the National Park Service. Chapter 6 77 The most common species associated with Box 6.2 Major Plant Species in Riparian lower elevation riparian communities are listed Communities in Arizona in Box 6.2 Detailed PLANT FACT SHEETS Arizona ash Fremont cottonwood with pictures of each species listed are located (Fraxinus velutina) (Populus fremontii) in Appendix C. Arizona sycamore Goodding’s willow (Platanus wrightii) (Salix gooddingii) Arizona walnut Mesquite The most common species associated with (Juglans major) (Prosopis spp.) lower elevation riparian communities are listed Cane bluestem Salt cedar in Box 6.2 Detailed PLANT FACT SHEETS (Bothriochloa barbinodis) (Tamarix spp.) with pictures of each species listed are located Deergrass Seep willow in Appendix C. (Mulenbergia rigens) (Baccharis glutinosa) Box 6.3 Major Riparian Plant Species Associated with Other Communities in Arizona Pinyon-Juniper and Oak Mixed Conifer Forest Ponderosa Pine Forest Chaparral Woodland Bigtooth maple Arizona alder Arizona alder Arizona ash (Acer grandidentatum) (Alnus oblongifolia) (Alnus oblongifolia) (Fraxinus velutina) Boxelder Arizona ash Arizona sycamore Arizona sycamore (Acer negundo) (Fraxinus velutina) (Platanus wrightii) (Platanus wrightii) Narrowleaf cottonwood Arizona walnut Arizona walnut Arizona walnut (Populus angustifolia) (Juglans major) (Juglans major) (Juglans major) Quaking aspen Boxelder Fremont cottonwood Fremont cottonwood (Populus tremuloides) (Acer negundo) (Populus fremontii) (Populus fremontii) Historic Fire Regime Although there is little historical information Although fires are thought to have been historically regarding the role of wildland fire in riparian uncommon in riparian vegetation communities, vegetation communities, evidence suggests that fire there are accounts of fires spreading from adjacent was not a significant factor (Austin and Wolf 2001). communities (Davis 1982). There are also accounts First, the dominant tree species found in riparian of Native American tribes setting fires in riparian areas are not considered to be fire-adapted (USFWS areas to rejuvenate vegetation for the benefit of game 2002). Trees typically do not have thick, protective animals and birds (Williams 1994) and to clear areas bark nor do they regenerate quickly after being for planting (Austin and Wolf 2001). damaged by fire. In addition, the dominant plants in riparian areas do not require fire to germinate their seeds like the ponderosa pine trees discussed in Chapter 2. Riparian trees do, however, have seeds that respond to other environmental disturbances Although there is little historical - most commonly flooding (Dwire and Kauffman information regarding the role of fire 2003). in riparian ecosystems, evidence Second, plants in riparian vegetation communities suggests that fire was not a significant contain more moisture than plants in other vegetation