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~: ~ - BiTCTERFLY ASSEMBLAGES ALONG THE LOWER COLORADO RIVER $O1 Recent syntheses of river restoration literature (Stanford et al., 1996; Poff et al., 1997) suggest that attempts to recover systems need to include, to some degree, the master variable of river flow. Gore and . Shields (1995) suggest that interactions between the main channel, backwaters, and floodplains are key to the rehabilitation of large rivers. We agree, and suggest that focus of restoration efforts on restoring hydrological processes, along with control of exotics, rather than simply planting cottonlwoods in xerified floodplain areas would be more successful in restoring butterfly assemblages. Sites that we studied along the Colorado River were static anti disconnected from the river, without the dynamic qualities associated with natural systems. Restoring hydrology would aid in flushing salts from soils and in developing natural levels of ground water. Destructive floods probably help maintain environmental heterogeneity that has been found important for continued survival of some butterfly populations (Singer,, 1972). Early life-history stages of butterflies may require food plants that exist in a particular growth-form or microhabitat (Thomas, 1991) more likely to be found in a heterogenous environment. Without the proper hydrology and accompanying disturbance, a revegetated site that could support a butterfly assemblage similar to what originally occurred would. need to be intensively managed. Managers would need to be continually responsible for transporting butterfly assemblages, assuring the presence of riparian trees of various types and ages, and of nectar plants, maintaining moist soils, and disturbing areas "to prevent dominance by exotic grasses. This study finds little evidence that butterfly assemblages at revegetated sites tend toward more natural riparian assemblages. We hypothesize that, along with climatic setting, determinant abiotic factors of the pre-dam riparian butterfly assemblage were largely associated with annual flooding. Important factors to butterfly assemblages that are largely lacking at revegetated sites include nectar resources, larval host- plants, closed canopies, high quality leaf material, habitat heterogeneity, and presence of riparian corridors. All of these are directly or indirectly influenced by river regulation and water extraction: . , _. _ . ~: =:..__ ACKNOWLEDGEMENTS + '.r "' We thank personnel of the Bill Williams River, Cibola, and Havasu National Wildlife Refuges and thy' `= Colorado River Indian Tribes for site access. -Rick Wydoski helped with butterfly collecting and Rrck;; Roline and Jim Brock reviewed an early draft. Thanks to John Swett for obtaining part of, the ` project; funding (BOR. LC090~. Ray Stanford helped with butterfly identifcations and Guy Nesum identifted Baccharls from the area.. Baccharis specimens are deposited at the University of Texas in Austin and ' butterflies with the C.P. Gillette Museum of Arthropod Diversity, Colorado State University... Copyright ©1999 John Wiley & Sons, Ltd. Regul. Rivers: Res. Mgm~. 15: 485-504 (1999) _ ~: