9530 - Laserfiche WebLink

Home Browse Search

498 S.M. NELSON AND D.C. ANDERSEN PopuluslSalix feeder, was present at BW, but also seen at No Name Lake and the 1993 revegetation site at Havasu Refuge, both of which had closed-canopy stands of cottonwood. Many relatively rare species were only found at BW; 32% of the species found at BW were unique to that site. Unique species ranged from 0% to 7% at other sites (Appendix A). Phreatophyte-dependent butterflies The phreatophyte-dependent butterflies Calephelis nemesis and Limenitis archippus were only detected at BW, despite their presence in the 1930s along the lower Colorado River near Blythe, California (Emmet and Emmet, 1973). The larval host plant of C. nemesis is seepwillow (Scott, 1986), a plant found at BW but not at any revegetated site. C. nemesis was successfully reared on seepwillow, but not on Emory baccharis (a congener common to revegetated sites), in laboratory trials (Nelson, unpublished data). seepwillow was an important nectar plant to C. nemesis and other butterflies at Bill Williams, where it bloomed for much of the year. In contrast, Emory baccharis was observed in bloom only in November. Seepwillow was once widespread on the lower Colorado River (Grinnell, 1914; Dill, 1944; also see range map in Benson and- Darrow, 1981). Seepwillow, adapted to disturbance (Bendix, 1994) and sensitive to groundwater change (Stromberg et al., 1996), may have been replaced along the lower Colorado by a more xeric species, a typical effect of regulation (Ward and Stanford, 1995). Increased soil salinity (Busch and Smith, 1995) may also haveled to loss of seepwillow in the area. Other Baccharis species may have high salt tolerances (e.g., Boldt and Robbins, 1994) that would favor. replacement of non-halophytes. Both Populus and Salix are larval host plants of Limenitis archippus, but this butterfly has not been found at revegetated sites containing these plants. Their absence may. be related to low amounts of nectar sources at these sites (Figure 7}, or perhaps the low quality food that leaf material,:at most of these xerified _.. sites may repiesenf: Busch and Smith (1995) found cottonwoods growing at BW have.greater nllmbers of leaves and leaf areas-than thos along the mainstem-(highly regulated} Colorado River. Host- plant growth- form may affect suitability-forbutterflies (Thomas; 1991)-and the-lack of early age classes of woody plants ~ctrt ~Seepwlllow ®Willow Tamarisk ®Mesquite ®Othertrees/shrubs ®Herbaceousplants ®Arrowweed ®Alkali Heliotrope r~~~~'~rr'r~~; Tamarisk R96 R93 R90 R87 R78 Bill Williams Figure 7. Types and relative amounts of nectar sources found at sites in 1997. Pie area indicates number of nectar sources relative to the number at the Bill Williams River site Copyright ©]999 John Wiley & Sons, Ltd. Regul. Riuers: Res. Mgmt. 15: 485-504 (1999)